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+The Project Gutenberg EBook of Sex-linked Inheritance in Drosophila, by 
+Thomas Hunt Morgan and Calvin B. Bridges
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Sex-linked Inheritance in Drosophila
+
+Author: Thomas Hunt Morgan
+        Calvin B. Bridges
+
+Release Date: November 18, 2010 [EBook #34368]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK SEX-LINKED INHERITANCE IN DROSOPHILA ***
+
+
+
+
+Produced by Bryan Ness, Keith Edkins and the Online
+Distributed Proofreading Team at https://www.pgdp.net (This
+book was produced from scanned images of public domain
+material from the Google Print project.)
+
+
+
+
+
+Transcriber's note: A few typographical errors have been corrected: they
+are listed at the end of the text.
+
+       *       *       *       *       *
+
+
+Page numbers enclosed by curly braces (example: {25}) have been
+incorporated to facilitate the use of the Table of Contents.
+
+       *       *       *       *       *
+
+
+Tables which have been divided into two parts widthwise are marked with a
+double ~ on the original common edge.
+
+       *       *       *       *       *
+
+
+SEX-LINKED INHERITANCE IN
+DROSOPHILA
+
+BY
+
+T. H. MORGAN AND C. B. BRIDGES
+
+
+
+[Illustration]
+
+
+
+WASHINGTON
+PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON
+1916
+
+
+
+CARNEGIE INSTITUTION OF WASHINGTON
+PUBLICATION NO. 237.
+
+
+
+PRESS OF GIBSON BROTHERS, INC.
+WASHINGTON, D. C.
+
+       *       *       *       *       *
+
+
+{3}
+
+CONTENTS.
+
+                                                                   PAGE.
+
+  PART I. INTRODUCTORY                                                5
+
+      Mendel's law of segregation                                     5
+      Linkage and chromosomes                                         5
+
+      Crossing-over                                                   7
+
+      The Y chromosome and non-disjunction                            8
+
+      Mutation in _Drosophila ampelophila_                           10
+      Multiple allelomorphs                                          11
+          Sex-linked lethals and the sex ratio                       14
+      Influence of the environment on the realization of two
+          sex-linked characters                                      16
+      Sexual polymorphism                                            17
+      Fertility and sterility in the mutants                         18
+      Balanced inviability                                           19
+      How the factors are located in the chromosomes                 20
+      The sex-linked factors of _Drosophila_                         21
+      Map of chromosome X                                            22
+      Nomenclature                                                   24
+
+  PART II. NEW DATA                                                  25
+      White                                                          25
+      Rudimentary                                                    25
+      Miniature                                                      26
+      Vermilion                                                      27
+      Yellow                                                         27
+      Abnormal abdomen                                               27
+      Eosin                                                          28
+      Bifid                                                          28
+          Linkage of bifid with yellow, with white, and with
+              vermilion                                              29
+          Linkage of cherry, bifid, and vermilion                    30
+      Reduplicated legs                                              31
+      Lethal 1                                                       31
+      Lethal 1a                                                      32
+      Spot                                                           33
+      Sable                                                          34
+          Linkage of yellow and sable                                35
+          Linkage of cherry and sable                                37
+          Linkage of eosin, vermilion, and sable                     37
+          Linkage of miniature and sable                             40
+          Linkage of vermilion, sable, and bar                       40
+      Dot                                                            44
+          Linkage of vermilion and dot                               44
+      Bow                                                            46
+          Bow by arc                                                 47
+      Lemon body-color                                               48
+          Linkage of cherry, lemon, and vermilion                    48
+      Lethal 2                                                       49
+      Cherry                                                         51
+          A system of quadruple allelomorphs                         51
+          Linkage of cherry and vermilion                            51
+          Compounds of cherry                                        52
+      Fused                                                          53
+           Linkage of eosin and fused                                54
+           Linkage of vermilion, bar, and fused                      56
+  {4}
+      Forked                                                         58
+          Linkage of vermilion and forked                            59
+          Linkage of cherry and forked                               59
+          Linkage of forked, bar, and fused                          60
+          Linkage of sable, rudimentary, and forked                  61
+          Linkage of rudimentary, forked, and bar                    62
+      Shifted                                                        63
+          Linkage of shifted and vermilion                           63
+          Linkage of shifted, vermilion, and bar                     64
+      Lethals _sa_ and _sb_                                          64
+      Bar                                                            66
+      Notch                                                          66
+      Depressed                                                      67
+          Linkage of depressed and bar                               67
+          Linkage of cherry, depressed, and vermilion                68
+      Club                                                           69
+          Genotypic club                                             70
+          Linkage of club and vermilion                              70
+          Linkage of yellow, club, and vermilion                     70
+          Linkage of cherry, club, and vermilion                     72
+      Green                                                          73
+      Chrome                                                         74
+      Lethal 3                                                       74
+      Lethal 3_a_                                                    75
+      Lethal 1_b_                                                    76
+      Facet                                                          76
+          Linkage of facet, vermilion, and sable                     77
+          Linkage of eosin, facet, and vermilion                     78
+      Lethal _sc_                                                    79
+      Lethal _sd_                                                    79
+      Furrowed                                                       80
+      Additional data for yellow, white, vermilion, and miniature    80
+          New data contributed by A. H. Sturtevant and H. J. Muller  82
+      Summary of the previously determined cross-over values         83
+      Summary of all data upon linkage of gens in chromosome I.      84
+      BIBLIOGRAPHY.                                                  86
+
+       *       *       *       *       *
+
+
+{5}
+
+PART I. INTRODUCTORY.
+
+MENDEL'S LAW OF SEGREGATION.
+
+Although the ratio of 3 to 1 in which contrasted characters reappear in the
+second or F_2 generation is sometimes referred to as Mendel's Law of
+Heredity, the really significant discovery of Mendel was not the 3 to 1
+ratio, but the segregation of the characters (or rather, of the germinal
+representatives of the characters) which is the underlying cause of the
+appearance of the ratio. Mendel saw that the characters with which he
+worked must be represented in the germ-cells by specific producers (which
+we may call factors), and that in the fertilization of an individual
+showing one member of a pair of contrasting characters by an individual
+showing the other member, the factors for the two characters meet in the
+hybrid, and that _when the hybrid forms germ-cells the factors segregate
+from each other without having been contaminated one by the other._ In
+consequence, half the germ-cells contain one member of the pair and the
+other half the other member. When two such hybrid individuals are bred
+together the combinations of the pure germ-cells give three classes of
+offspring, namely, two hybrids to one of each of the pure forms. Since the
+hybrids usually can not be distinguished from one of the pure forms, the
+observed ratio is 3 of one kind (the dominant) to 1 of the other kind (the
+recessive).
+
+There is another discovery that is generally included as a part of Mendel's
+Law. We may refer to this as the _assortment_ in the germ-cells of the
+products of the segregation of two or more pairs of factors. If assortment
+takes place according to chance, then definite F_2 ratios result, such as
+9:3:3:1 (for two pairs) and 27:9:9:9:3:3:3:1 (for three pairs), etc. Mendel
+obtained such ratios in peas, and until quite recently it has been
+generally supposed that free assortment is the rule when several pairs of
+characters are involved. But, as we shall try to show, the emphasis that
+has been laid on these ratios has obscured the really important part of
+Mendel's discovery, namely, _segregation_; for with the discovery in 1906
+of the fact of linkage the ratios based on free assortment were seen to
+hold only for combinations of certain pairs of characters, not for other
+combinations. But the principle of segregation still holds for each pair of
+characters. Hence segregation remains the cardinal point of Mendelism.
+Segregation is to-day Mendel's Law.
+
+LINKAGE AND CHROMOSOMES.
+
+It has been found that when _certain_ characters enter a cross together
+(_i. e._, from the same parent) their factors tend to pass into the same
+gamete of the hybrid, with the result that other ratios than the chance
+ratios described by Mendel are found in the F_2 generation. {6} Such cases
+of linkage have been described in several forms, but nowhere on so
+extensive a scale as in the pomace fly, _Drosophila ampelophila_. Here,
+over a hundred characters that have been investigated as to their linkage
+relations are found to fall into four groups, the members of each group
+being linked, in the sense that they tend to be transmitted to the gametes
+in the same combinations in which they entered from the parents. The
+members of each group give free assortment with the members of any of the
+other three groups. A most significant fact in regard to the linkage shown
+by the _Drosophila_ mutants is that _the number of linked groups
+corresponds to the number of pairs of the chromosomes._ If the gens for the
+Mendelian characters are carried by the chromosomes we should expect to
+find demonstrated in _Drosophila_ that there are as many groups of
+characters that are inherited together as there are pairs of chromosomes,
+provided the chromosomes retain their individuality. The evidence that the
+chromosomes are structural elements of the cell that perpetuate themselves
+at every division has continually grown stronger. That factors have the
+same distribution as the chromosomes is clearly seen in the case of
+sex-linked characters, where it can be shown that any character of this
+type appears in those individuals which from the known distribution of the
+X chromosomes must also contain the chromosome in question. For example, in
+_Drosophila_, as in many other insects, there are two X chromosomes in the
+cells of the female and one X chromosome in the cells of the male. There is
+in the male, in addition to the X, also a Y chromosome, which acts as its
+mate in synapsis and reduction. After reduction each egg carries an X
+chromosome. In the male there are two classes of sperm, one carrying the X
+chromosome and the other carrying the Y chromosome. Any egg fertilized by
+an X sperm produces a female; any egg fertilized by a Y sperm produces a
+male. The scheme of inheritance is as follows.
+
+            +------------------------------+
+            |                              |
+            | Eggs                    X--X |
+            | Sperm                   X--Y |
+            +------------------------------+
+            | Daughter                 XX  |
+            | Son                      XY  |
+            |                              |
+            +------------------------------+
+
+The sons get their single X chromosome from their mother, and should
+therefore show any character whose gen is carried by such a chromosome. In
+sex-linked inheritance all sons show the characters of their mother. A male
+transmits his sex-linked character to his daughters, who show it if
+dominant and conceal it if recessive. But any daughter will transmit such a
+character, whether dominant or recessive, to half of her sons. The path of
+transmission of the gen is the same as the path followed by the X
+chromosome, received here {7} from the male. Many other combinations show
+the same relations. In the case of non-disjunction, to be given later,
+there is direct experimental evidence of such a nature that there can no
+longer be any doubt that the X chromosomes are the carriers of certain gens
+that we speak of as sex-linked. This term (sex-linked) is intended to mean
+that such characters are carried by the X chromosome. It has been objected
+that this use of the term implies a knowledge of a factor for sex in the X
+chromosome to which the other factors in that chromosome are linked; but in
+fact we have as much knowledge in regard to the occurrence of a sex factor
+or sex factors in the X chromosome as we have for other factors. It is true
+we do not know whether there is more than one sex-factor, because there is
+no crossing-over in the male (the heterozygous sex), and crossing-over in
+the female does not influence the distribution of sex, since like parts are
+simply interchanged. It follows from this that we are unable as yet to
+locate the sex factor or factors in the X chromosome. The fact that we can
+not detect crossing-over under this condition is not an argument against
+the occurrence of linkage. We are justified, therefore, in speaking of the
+factors carried by the X chromosome as sex-linked.
+
+CROSSING-OVER.
+
+When two or more sex-linked factors are present in a male they are always
+transmitted together to his daughters, as must necessarily be the case if
+they are carried by the unpaired X chromosome. If such a male carrying, let
+us say, two sex-linked factors, is mated to a wild female, his daughters
+will have one X chromosome containing the factors for both characters,
+derived from the father, and another X chromosome that contains the factors
+that are normal for these two factors (the normal allelomorphs). The sons
+of such a female will get one or the other of these two kinds of
+chromosomes, and should be expected to be like the one or the other
+grandparent. In fact, most of the sons are of these two kinds. But, in
+addition, there are sons that show one only of the two original mutant
+characters. Clearly an interchange has taken place between the two X
+chromosomes in the female in such a way that a piece of one chromosome has
+been exchanged for the homologous piece of the other. The same conclusion
+is reached if the cross is made in such a way that the same two sex-linked
+characters enter, but, one from the mother and the other from the father.
+The daughter gets one of her sex chromosomes from her mother and the other
+from her father. She should produce, then, two kinds of sons, one like her
+mother and one like her father. In fact, the majority of her sons are of
+these two kinds, but, in addition, there are two other kinds of sons, one
+kind showing both mutant characters, the other kind showing normal
+characters. Here again the results must be due to interchange between the
+two X's in the hybrid female. _The number of_ {8} _the sons due to exchange
+in the two foregoing crosses is always the same, although they are of
+contrary classes._ Clearly, then, the interchange takes place irrespective
+of the way in which the factors enter the cross. We call those classes that
+arise through interchange between the chromosomes "cross-over classes" or
+merely "cross-overs." The phenomenon of holding together we speak of as
+linkage.
+
+By taking a number of factors into consideration at the same time it has
+been shown that _crossing-over involves large pieces of the chromosomes_.
+The X chromosomes undergo crossing-over in about 60 per cent of the cases,
+and the crossing-over may occur at any point along the chromosome. When it
+occurs once, whole ends (or halves even) go over together and the exchange
+is always equivalent. If crossing-over occurs twice at the same time a
+middle piece of one chromosome is intercalated between the ends of the
+other chromosome. This process is called double crossing-over. It occurs
+not oftener than in about 10 per cent of cases for the total length of the
+X chromosome. Triple crossing-over in the X chromosome is extremely rare
+and has been observed only about a half dozen times.
+
+While the genetic evidence forces one to accept crossing-over between the
+sex chromosomes in the female, that evidence gives no clue as to how such a
+process is brought about. There are, however, certain facts familiar to the
+cytologist that furnish a clue as to how such an interchange might take
+place. When the homologous chromosomes come together at synapsis it has
+been demonstrated, in some forms at least, that they twist about each other
+so that one chromosome comes to lie now on the one side now on the other of
+its partner. If at some points the chromosomes break and the pieces on the
+same side unite and pass to the same pole of the karyokinetic spindle, the
+necessary condition for crossing-over will have been fulfilled.
+
+THE Y CHROMOSOME AND NON-DISJUNCTION.
+
+Following Wilson's nomenclature, we speak of both X and Y as sex
+chromosomes. Both the cytological and the genetic evidence shows that when
+two X chromosomes are present a female is produced, when one, a male. This
+conclusion leaves the Y chromosome without any observed relation to
+sex-determination, despite the fact that the Y is normally present in every
+male and is confined to the male line. The question may be asked, and in
+fact has been asked, why may not the presence of the Y chromosome determine
+that a male develop and its absence that a female appear? The only answer
+that has yet been given, outside of the work on _Drosophila_, is that since
+in some insects there is no Y chromosome, there is no need to make such an
+assumption. But in _Drosophila_ direct proof that Y has no such function is
+furnished by the evidence discovered by Bridges in the case of
+non-disjunction. (Bridges, 1913, 1914, 1916, and unpublished results.) {9}
+
+Ordinarily all the sons and none of the daughters show the recessive
+sex-linked characters of the mother when the father carries the dominant
+allelomorph. The peculiarity of non-disjunction is that sometimes a female
+produces a daughter like herself or a son like the father, although the
+rest of the offspring are perfectly regular. For example, a vermilion
+female mated to a wild male produces vermilion sons and wild-type
+daughters, but rarely also a vermilion daughter or a wild-type son. The
+production of these exceptions (primary exceptions) by a normal XX female
+must be due to an aberrant reduction division at which the two X
+chromosomes fail to disjoin from each other. In consequence both remain in
+the egg or both pass into the polar body. In the latter case an egg without
+an X chromosome is produced. Such an egg fertilized by an X sperm produces
+a male with the constitution XO. These males received their single X from
+their father and therefore show the father's characters. While these XO
+males are exceptions to sex-linked inheritance, the characters that they do
+show are perfectly normal, that is, the miniature or the bar or other
+sex-linked characters that the XO male has are like those of an XY male,
+showing that the Y normally has no effect upon the development of these
+characters. But that the Y does play some positive role is proved by the
+fact that all the XO males have been found to be absolutely sterile.
+
+While the presence of the Y is necessary for the fertility of the male, it
+has no effect upon sex itself. This is shown even more strikingly by the
+phenomenon known as secondary non-disjunction. If the two X chromosomes
+that fail to disjoin remain in the egg, and this egg is fertilized by a Y
+sperm, an XXY individual results. This is a female which is like her mother
+in all sex-linked characters (a matroclinous exception), since she received
+both her X chromosomes from her mother and none from her father. As far as
+sex is concerned this is a perfectly normal female. The extra Y has no
+effect upon the appearance of the characters, even in the case of eosin,
+where the female is much darker than the male. The only effect which the
+extra Y has is as an extra wheel in the machinery of synapsis and
+reduction; for, on account of the presence of the Y, both X's of the XXY
+female are sometimes left within the ripe egg, a process called secondary
+non-disjunction. In consequence, an XXY female regularly produces
+exceptions (to the extent of about 4 per cent). A small percentage of
+reductions are of this XX-Y type; the majority are X-XY. The XY eggs,
+produced by the X-XY reductions, when fertilized by Y sperm, give XYY
+males, which show no influence of the extra Y except at synapsis and
+reduction. By mating an XXY female to an XYY male, XXYY females have been
+produced and these are perfectly normal in appearance. We may conclude from
+the fact that visibly indistinguishable males have been produced with the
+formulas XO, XY, and XYY, and {10} likewise females with the formulas XX,
+XXY, and XXYY, that the Y is without effect either on the sex or on the
+visible characters (other than fertility) of the individual.
+
+The evidence is equally positive that sex is quantitatively determined by
+the X chromosome--that two X's determine a female and one a male. For in
+the case of non-disjunction, a zero or a Y egg fertilized by an X sperm
+produces a male, while conversely an XX egg fertilized by a Y sperm
+produces a female. It is thus impossible to assume that the X sperms are
+normally female-producing because of something else than the X or that the
+Y sperm produce males for any other reason than that they normally
+fertilize X eggs. Both the X and the Y sperm have been shown to produce the
+sex opposite to that which they normally produce when they fertilize eggs
+that are normal in every respect, except that of their X chromosome
+content. These facts establish experimentally that sex is determined by the
+combinations of the X chromosomes, and that the male and female
+combinations are the causes of sex differentiation and are not simply the
+results of maleness and femaleness already determined by some other agent.
+
+Cytological examination has demonstrated the existence of one XXYY female,
+and has checked up the occurrence in the proper classes and proportions of
+the XXY females. Numerous and extensive breeding-tests have been made upon
+the other points discussed. The evidence leaves no escape from the
+conclusion that the genetic exceptions are produced as a consequence of the
+exceptional distribution of the X chromosomes and that the gens for the
+sex-linked characters are carried by those chromosomes.
+
+MUTATION IN DROSOPHILA AMPELOPHILA.
+
+The first mutants were found in the spring of 1910. Since then an
+ever-increasing series of new types has been appearing. An immense number
+of flies have come under the scrutiny of those who are working in the
+Zoological Laboratory of Columbia University, and the discovery of so many
+mutant types is undoubtedly due to this fact. But that mutation is more
+frequent in _Drosophila ampelophila_ than in some of the other species of
+_Drosophila_ seems not improbable from an extensive examination of other
+types. It is true a few mutants have been found in other _Drosophilas_, but
+relatively few as compared with the number in _D. ampelophila_. Whether
+_ampelophila_ is more prone to mutate, or whether the conditions under
+which it is kept are such as to favor this process, we have no knowledge.
+Several attempts that we have made to produce mutations have led to no
+conclusive results.
+
+The mutants of _Drosophila_ have been referred to by Baur as "mutations
+through loss," but inasmuch as they differ in no respect that we can
+discover from other mutants in domesticated animals and plants, there is no
+particular reason for putting them into this category unless {11} to imply
+that new characters have not appeared, or that those that have appeared
+must be due to loss in the sense of absence of something from the
+germ-plasm.
+
+In regard to the first point, several of the mutants are characterized by
+what seem to be additions. For example, the eye-color sepia is darker than
+the ordinary red. At least three new markings have been added to the
+thorax. A speck has appeared at the base of the wing, etc. These are
+recessive characters, it is true, but the character "streak," which
+consists of a dark band added to the thorax, is a dominant. If dominance is
+supposed to be a criterion as to "presence," then it should be pointed out
+that among the mutants of _Drosophila_ a number of dominant types occur.
+But clearly we are not justified by these criteria in inferring anything
+whatever in regard to the nature of the change that takes place in the
+germ-plasm. Probably the only data which give a basis for attempting to
+decide the nature of the change in the germ-plasm are from cases where
+multiple allelomorphs are found. Several such cases are known to us, and
+two of these are found in the X chromosome group, namely, a quadruple
+system (white, eosin, cherry, red), and a triple system (yellow, spot,
+gray). In such cases each member acts as the allelomorph of any other
+member, and only two can occur in any one female, and only one in any male.
+If the normal allelomorph is thought of as the positive character, which
+one of the mutants is due to its loss or to its absence? If each is
+produced by a loss it must be a different loss that acts as an allelomorph
+to the other loss. This is obviously absurd unless a different idea from
+the one usually promulgated in regard to "absence" is held.
+
+MULTIPLE ALLELOMORPHS.
+
+It appears that Cuenot was the first to find a case (in mice) in which the
+results could be explained on the basis that more than two factors may
+stand in the relation of allelomorphs to each other. In other words, a
+given factor may become the partner of more than one other factor,
+although, in any one individual, no more than two factors stand in this
+relation. While it appears that his evidence as published was not
+demonstrative, and that, at the time he wrote, the possibility of such
+results being due to very close linkage could not have been appreciated as
+an alternative explanation, nevertheless it remains that Cuenot was right
+in his interpretation of his results and that the factors for yellow, gray,
+gray white-belly, and black in mice form a system of quadruple
+allelomorphs.
+
+There are at least two such systems among the factors in the first
+chromosome in _Drosophila_. The first of these includes the factor for
+white eyes, that for eosin eyes, and that for cherry eyes, and of course
+that allelomorph of these factors present in the wild fly and which when
+present gives the red color. In this instance the normal {12} allelomorph
+dominates all the other three, but in mice the mutant factor for yellow
+dominates the wild or "normal" allelomorph.
+
+The other system of multiple allelomorphs in the first chromosome is a
+triple system made up of yellow (body-color), spot (on abdomen), and their
+normal allelomorph--the factor in the normal fly that stands for "gray."
+
+In general it may be said that there are two principal ways in which it is
+possible to show that certain factors (more than two) are the allelomorphs
+of each other. First, if they are allelomorphs only two can exist in the
+same individual; and, in the case of sex-linked characters, while two may
+exist in the same female, only one can exist in the male, for he contains
+but one X chromosome. Second, all the allelomorphs should give the same
+percentages of crossing-over with each other factor in the same chromosome.
+
+It is a question of considerable theoretical importance whether these cases
+of multiple allelomorphs are only extreme cases of linkage or whether they
+form a system quite apart from linkage and in relation to normal
+allelomorphism. It may be worth while, therefore, to discuss this question
+more at length, especially because _Drosophila_ is one of the best cases
+known for such a discussion.
+
+The factors in the first chromosome are linked to each other in various
+degrees. When they are as closely linked as yellow body-color and white
+eyes crossing-over takes place only once in a hundred times. If two factors
+were still nearer together it is thinkable that crossing-over might be such
+a rare occurrence that it would require an enormous number of individuals
+to demonstrate its occurrence. In such a case the factors might be said to
+be completely linked, yet each would be supposed to have its normal
+allelomorph in the homologous chromosome of the wild type. Imagine, then, a
+situation in which one of these two mutant factors (a) enters from one
+parent and the other mutant factor (b) from the other parent. The normal
+allelomorph of a may be called A. It enters the combination with b, while
+the normal allelomorph B of b enters the combination with a. Since b is
+completely linked to A and a to B, the result will be the same as though a
+and b were the allelomorphs of each other, for in the germ-cells of the
+hybrid aBAb the assortment will be into aB and Ab, which is the same as
+though a and b acted as segregating allelomorphs.
+
+There is no way from Mendelian data by which this difference between a true
+case of multiple allelomorphs and one of complete linkage (as just
+illustrated) can be determined. There is, however, a different line of
+attack which, in a case like that of _Drosophila_, will give an answer to
+this question. The answer is found in the way in which the mutant factors
+arise. This argument has been fully developed in the book entitled "The
+Mechanism of Mendelian Inheritance," and will therefore not be repeated
+here. It must suffice to say that if two mutant {13} types that behave as
+allelomorphs of each other arise separately from the wild form, one of them
+must have arisen as a double mutation of two factors so close to each other
+as to be completely linked--a highly improbable occurrence when the
+infrequency of mutations is taken into consideration.[1] The evidence
+opposed to such an interpretation is now so strong that there can be little
+doubt that multiple allelomorphs have actually appeared.
+
+On _a priori_ grounds there is no reason why several mutative changes might
+not take place in the same locus of a chromosome. If we think of a
+chromosome as made up of a chain of chemical particles, there may be a
+number of possible recombinations or rearrangements within each particle.
+Any change might make a difference in the end-product of the activity of
+the cell, and give rise to a new mutant type. It is only when one
+arbitrarily supposes that the only possible change in a factor is its loss
+that any serious difficulty arises in the interpretation of multiple
+allelomorphs.
+
+One of the most striking facts connected with the subject of multiple
+allelomorphs is that the same kind of change is effected in the same organ.
+Thus, in the quadruple system mentioned above, the color of the eye is
+affected. In the yellow-spot system the color of the body is involved. In
+mice it is the coat-color that is different in each member of the series.
+While this is undoubtedly a striking relation and one which seems to fit
+well with the idea that such effects are due to mutative changes in the
+same fundamental element that affects the character in question, yet on the
+other hand it would be dangerous to lay too much emphasis on this point,
+because any given organ may be affected by other factors in a similar
+manner, and also because a factor frequently produces more than a single
+effect. For instance, the factor that when present gives a white eye
+affects also the general yellowish pigment of the body. If red-eyed and
+white-eyed flies are put for several hours into alcohol, the yellowish
+body-color of the white-eyed flies is freely extracted, but not that of the
+red-eyed flies. In the living condition the difference between the
+body-colors of the red- and of the white-eyed flies is too slight to be
+visible, but after extraction in alcohol the difference is striking. There
+are other effects also that follow in the wake of the white factor. Now, it
+is quite conceivable that in some specific case one of the effects might be
+more striking than the one produced in that organ more markedly affected by
+the other factor of the allelomorphic series. In such a case the relation
+mentioned above might seemingly disappear. For this reason it is well not
+to insist too strongly on the idea that multiple allelomorphs affect the
+same part in the same way, even although at present that appears to be the
+rule for all known cases.
+
+{14}
+
+SEX-LINKED LETHALS AND THE SEX RATIO.
+
+Most of the mutant types of _Drosophila_ show characteristics that may be
+regarded as superficial in so far as they do not prevent the animal from
+living in the protected life that our cultures afford. Were they thrown
+into open competition with wild forms, or, better said, were they left to
+shift for themselves under natural conditions, many or most of the types
+would no doubt soon die out. So far as we can see, there is no reason to
+suppose that the mutations which can be described as superficial are
+disproportionally more likely to occur than others. Of course, superficial
+mutations are more likely to survive and hence to be seen; while if
+mutations took place in important organs some of them would be expected to
+affect injuriously parts essential to the life of the individual and in
+consequence such an individual perishes. The "lethal factors" of
+_Drosophila_ may be supposed to be mutations of some such nature; but as
+yet we have not studied this side of the question sufficiently, and this
+supposed method of action of the lethals is purely speculative. Whatever
+the nature of the lethals' action, it can be shown that from among the
+offspring obtained from certain stocks expected classes are missing, and
+the absence of these classes can be accounted for on the assumption that
+there are present mutant factors that follow the Mendelian rule of
+segregation and which show normal linkage to other factors, but whose only
+recognizable difference from the normal is the death of those individuals
+which receive them. The numerical results can be handled in precisely the
+same way as are other linkage results.
+
+There are some general relations that concern the lethals that may be
+mentioned here, while the details are left for the special part or are
+found in the special papers dealing with these lethals. A factor of this
+kind carried by the X chromosome would be transmitted in the female line
+because the female, having two X chromosomes, would have one of them with
+the normal allelomorph (dominant) of the lethal factor carried by the other
+X chromosome. Half of her sons would get one of her X's, the other half the
+other. Those sons that get the lethal X will die, since the male having
+only one X lacks the power of containing both the lethal and its normal
+allelomorph. The other half of the sons will survive, but will not transmit
+the lethal factor. In all lethal stocks there are only half as many sons as
+daughters. The heterozygous lethal-bearing female, fertilized by a normal
+male, will give rise to two kinds of daughters; one normal in both X's, the
+other with a normal X and a lethal-bearing X chromosome. The former are
+always normal in behavior, and the latter repeat in their descendants the
+2:1 sex-ratio.
+
+Whether a female bearing the same lethal twice (_i.e._, one homozygous for
+a given lethal) would die, can not be stated, for no such females are
+obtainable, because the lethal males, which alone could bring about {15}
+such a condition, do not exist. The presumption is that a female of this
+kind would also die if the lethal acts injuriously on some vital function
+or structure.
+
+Since only half of the daughters of the lethal-bearing females carry the
+lethal, the stock can be maintained by breeding daughters separately in
+each generation to insure obtaining one which repeats the 2:1 ratio. There
+is, however, a much more advantageous way of carrying on the stock--one
+that also confirms the sufficiency of the theory.
+
+In carrying on a stock of a lethal, advantage can be taken of linkage. A
+lethal factor has a definite locus in the chromosome; if, then, a
+lethal-bearing female is crossed to a male of another stock with a
+recessive character whose factor lies in the X chromosome very close to the
+lethal factor, half the daughters will have lethal in one X and the
+recessive in the other. The lethal-bearing females can be picked out from
+their sisters by the fact that they give a 2:1 sex-ratio, and by the fact
+that nearly all the sons that do survive show the recessive character. If
+such females are tested by breeding to the recessive males, then the
+daughters which do not show the recessive carry the lethal, except in the
+few cases of crossing-over. Thus in each generation the normal females are
+crossed to the recessive males with the assurance that the lethal will not
+be lost. If instead of the single recessive used in this fashion, a double
+recessive of such a sort that one recessive lies on each side of the lethal
+is used, then in each generation the females which show neither recessive
+will almost invariably contain the lethal, since a double cross-over is
+required to remove the lethal.
+
+It is true that females carrying two _different_ lethals might arise and
+not die, because the injurious effect of each lethal would be dominated by
+its allelomorph in the other X chromosome. Such females can not be obtained
+by combining two existing lethals, since lethal males do not survive. They
+can occur only through a new lethal arising through mutation in the
+homologous chromosome of a female that already carries one lethal. Rare as
+such an event must be, it has occurred in our cultures thrice. The presence
+of a female of this kind will be at once noticed by the fact that she
+produces no sons, or very rarely one, giving in consequence extraordinary
+sex-ratios. The rare appearance of a son from such a female can be
+accounted for in the following way: If crossing-over occurs between her X
+chromosomes the result will be that one X will sometimes contain two
+lethals, the other none. The latter, if it passes into a male, will lead to
+the development of a normal individual. The number of such males depends on
+the distance apart of the two lethals in the chromosome. There is a crucial
+test of this hypothesis of two lethals in females giving extraordinary
+ratios. This test has been applied to the cases in which such females were
+found, by Rawls (1913), by Morgan (1914_c_), and again by Stark (1915), and
+it has been found to confirm the explanation. The daughters of {16} such a
+female should all (excepting a rare one due to crossing-over) give 2:1
+ratios, because each daughter must get one or the other X chromosome of her
+mother, that is, one or the other lethal. Although the mother was
+fertilized by a normal male, every daughter is heterozygous for one or the
+other of the lethal factors. The daughters of the two-lethal females differ
+from the daughters of the one-lethal female in that the former mother, as
+just stated, gives all lethal-bearing daughters; the latter transmits her
+lethal to only half of her daughters.
+
+INFLUENCE OF THE ENVIRONMENT ON THE REALIZATION OF TWO SEX-LINKED
+CHARACTERS.
+
+The need of a special environment in order that certain mutant characters
+may express themselves has been shown for abnormal abdomen (Morgan,
+1912_d_, 1915_b_) and for reduplication of the legs (Hoge, 1915). In a
+third type, club, described here (page 69), the failure of the unfolding of
+the wing which occurs in about 20 per cent of the flies is also without
+much doubt an environmental effect, but as yet the particular influence
+that causes the change is unknown.
+
+A very extensive series of observations has been made on the character
+called abnormal abdomen. In pure cultures kept moist with abundance of
+fresh food all the flies that hatch for the first few days have the black
+bands of the abdomen obliterated or made faint and irregular. As the
+bottles get dry and the food becomes scarce the flies become more and more
+normal, until at last they are indistinguishable from the normal flies.
+Nevertheless these normal-looking flies will give rise in a suitable
+environment to the same kind of flies as the very abnormal flies first
+hatched. By breeding from the last flies of each culture, and in dry
+cultures, flies can be bred from normal ancestors for several generations,
+and then by making the conditions favorable for the appearance of the
+abnormal condition, the flies will be as abnormal as though their ancestors
+had always been abnormal. Here, then, is a character that is susceptible to
+the variations in the environment, yet whatever the realized condition of
+the soma may be, that condition has no effect whatever on the nature of the
+germ-plasm. A more striking disproof of the theory of the inheritance of
+acquired characters would be hard to find.
+
+A demonstration is given in this instance of the interaction between a
+given genotypic constitution and a special environment. The character
+abnormal is a sex-linked dominant. Therefore, if an abnormal male is mated
+to a wild female the daughters are heterozygous for abnormal, while the
+sons, getting their X chromosome from their mother, are entirely normal. In
+a wet environment all the daughters are abnormal and the sons normal. As
+the culture dries out the daughters' color becomes normal in appearance.
+But while the sons {17} will never transmit abnormality to any of their
+descendants in any environment, the daughters will transmit (if bred to
+normal males) in a suitable environment their peculiarity to half of their
+daughters and to half of their sons. The experiment shows convincingly that
+the abnormal abdomen appears in a special environment only in those flies
+that have a given genotypic constitution.
+
+As the cultures dry out the abnormal males are the first to change over to
+normal, then the heterozygous females, and lastly the homozygous females.
+It is doubtful if any far-reaching conclusion can be drawn from this
+series, because the first and second classes differ from each other not
+only in the presence of one or of two factors for abnormal, but also by the
+absence in the first case (male) of an entire X chromosome with its
+contained factors. The second and third classes differ from each other only
+by the abnormal factor.
+
+Similar results were found in the mutant type called reduplicated legs,
+which is a sex-linked recessive character that appears best when the
+cultures are kept at about 10deg C. As Miss M. A. Hoge has shown, this
+character then becomes realized in nearly all of the flies that have the
+proper constitution, but not in flies of normal constitution placed in the
+same environment. Here the effect is produced by cold.
+
+SEXUAL POLYMORPHISM.
+
+Outside the primary and secondary sexual differences between the male and
+the female, there is a considerable number of species of animals with more
+than one kind of female or male. Darwin and his followers have tried to
+explain such cases on the grounds that more than one kind of female (or
+male) might arise through natural selection, in consequence of some
+individuals mimicking a protected species. It is needless to point out here
+how involved and intricate such a process would be, because the mutation
+theory has cut the Gordian knot and given a simpler solution of the origin
+of such diandromorphic and digynomorphic conditions.
+
+In _Drosophila_ a mutant, eosin eye-color, appeared in which the female has
+darker eyes than the male. If such stock is crossed with cherry (another
+sex-linked recessive mutant, allelomorphic to eosin) the females in the F_2
+generation are alike (for the pure eosin and the eosin-cherry compound are
+not separable), but the cherry males and the eosin males are quite
+different in appearance. Here we have a simulation, at least, of a
+diandromorphic species. Such a group perpetuates itself, giving one type of
+female (inasmuch as eosin and cherry females are very closely similar) and
+two types of males, only one of which is like the females. A population of
+this kind is very directly comparable to certain polymorphic types that
+occur in nature. In _Colias philodice_ there is one type of male, yellow,
+and two types of females, yellow and {18} white. In _Colias eurydice_ the
+male is orange and the females are orange or white. In _Papilio turnus_ the
+male is yellow and the females either yellow or black. Those cases are
+directly comparable to an eosin-cherry population, except that in
+Lepidoptera the female is heterozygous for the sex differential, in Diptera
+the male.
+
+Since in _Drosophila_ the results are explicable on a sex-linked basis, a
+similar explanation may apply to polymorphism in butterflies. By suitable
+combinations of eosin and cherry most of the cases of polymorphism in
+butterflies may be simulated. To simulate the more complex cases, such as
+that of _Papilio polytes_ and _memnon_, another allelomorph like eosin
+would have to be introduced. A population of mixed cherry and white would
+give three somatic types of females (cherry, cherry-white, and white) and
+two of males (cherry and white).
+
+FERTILITY AND STERILITY IN THE MUTANTS.
+
+Aside from the decrease in fertility that occurs in certain stocks (a
+question that need not be treated here), there are among the types
+described in the text two cases that call for special comment. When the
+mutant type called "rudimentary" was first discovered, it was found that
+the females were sterile but the males were fully fertile. Later work has
+revealed the nature of the sterility of the female. The ovaries are present
+and in the young flies appear normal, but while in the normal flies the
+eggs in the posterior portion enlarge rapidly during the first few days
+after hatching, in the rudimentary females only a very few (about 15) eggs
+enlarge. The other eggs in the ovary remain at a lower stage of their
+development. Rarely the female lays a few eggs; when she does so some of
+the eggs hatch, and if she has been mated to a rudimentary male, the
+offspring are rudimentary females and males. The rudimentary females mate
+in the normal time with rudimentary or with normal males, and their sexual
+behavior is normal. Their sterility is therefore due to the failure of the
+eggs to develop properly. Whether in addition to this there is some
+incompatibility between the sperm and the eggs of this type (as supposed to
+be the case at one time) is not conclusively disproved, but is not probable
+from the evidence now available.
+
+In the mutant called "fused" the females are sterile both with wild males
+and with males from their own stock. An examination of the ovaries of these
+females, made by Mr. C. McEwen, shows clearly that there are fewer than the
+normal number of mature eggs, recalling the case of rudimentary.
+
+It should be noticed that there is no apparent relation between the
+sterility of these two types and the occurrence of the mutation in the X
+chromosome, because other mutations in the X do not cause sterility, and
+there is sterility in other mutant types that are due to factors in other
+chromosomes. {19}
+
+BALANCED INVIABILITY.
+
+The determination of the cross-over values of the factors was at first
+hindered because of the poor viability of some of the mutants. If the
+viability of each mutant type could be determined in relation to the
+viability of the normal, "coefficients of viability" could serve as
+corrections in working with the various mutant characters. But it was found
+(Bridges and Sturtevant, 1914) that viability was so erratic that
+coefficients might mislead. At the same time it was becoming more apparent
+that poor viability is no necessary attribute of a character, but depends
+very largely on the condition of culture. Competition among larvae was
+found to be the chief factor in viability. Mass cultures almost invariably
+have extremely poor viability, even though an attempt is made to supply an
+abundance of food. Special tests (Morgan and Tice, 1914) showed that even
+those mutants which were considered the very poorest in viability were
+produced in proportions fairly close to the theoretical when only one
+female was used for each large culture bottle and the amount and quality of
+food was carefully adjusted.
+
+For the majority of mutants which did well even under heavy competition in
+mass cultures the pair-breeding method reduced the disturbances due to
+viability to a point where they were negligible.
+
+Later a method was devised (Bridges, 1915) whereby mutations of poor
+viability could be worked with in linkage experiments fairly accurately and
+whereby the residual inviability of the ordinary characters could be
+largely canceled. This method consists in balancing the data of a certain
+class with poor viability by means of an equivalent amount of data in which
+the same class occurs as the other member of the ratio. Thus in obtaining
+data upon any linkage case it is best to have the total number of
+individuals made up of approximately equal numbers derived from each of the
+possible ways in which the experiment may be conducted. In the simplest
+case, in which the results are of the form AB:Ab:aB:ab, let us suppose that
+the class ab has a disproportionately low viability. If, then, ab occurs in
+an experiment as a cross-over class, that class will be too small and a
+false linkage value will be calculated. The remedy is to balance the
+preceding data by an equal amount of data in which ab occurs as a
+non-cross-over. In these latter the error will be the opposite of the
+previous one, and by combining the two experiments the errors should be
+balanced to give a better approximation to the true value. When equal
+amounts of data, secured in these two ways, are combined, all four classes
+will be balanced in the required manner by occurring both as
+non-cross-overs and as cross-overs. The error, therefore, should be very
+small. For three pairs of gens there are eight classes, and in order that
+each of them may appear as a non-cross-over, as each single cross-over, and
+as the double cross-over, four experiments must be made. {20}
+
+HOW THE FACTORS ARE LOCATED IN THE CHROMOSOMES.
+
+A character is in the first chromosome if it is transmitted by the
+grandfather to half of his grandsons, while, in the reciprocal cross, the
+mother transmits her character to all her sons (criss-cross inheritance)
+and to half of her granddaughters and to half of her grandsons; in other
+words, if the factor that differentiates the character has the same
+distribution as the X chromosome. If, however, a new mutant type does not
+show this sex-linked inheritance, its chromosome is determined by taking
+advantage of the fact that in _Drosophila_ there is no crossing-over in the
+male between factors in the same chromosome. For instance, if a new mutant
+type is found not to be sex-linked, its group is determined by the
+following tests: It is crossed to black, whose factor is known to be in the
+second chromosome, and to pink, whose factor lies in the third chromosome.
+If the factor of the new form should happen to be in the second chromosome,
+then, in the cross with black, no double recessive can appear, so that the
+F_{2} proportion is 2:1:1:0; but with pink, the mutant type should give the
+proportion 9:3:3:1, typical of free assortment.
+
+If, however, the factor of the new form is in the third chromosome, then,
+when crossed to black, the double recessive and the 9:3:3:1 proportion
+appear in F_{2}. But when crossed to pink no double recessive appears in
+F_{2}, and the proportion 2:1:1:0 occurs.
+
+If these tests show that the new mutant does not belong to either the
+second or third chromosome, that is, if both with black and with pink the
+9:3:3:1 ratio is obtained, then by exclusion the factor lies in the fourth
+chromosome, in which as yet only two factors have been found.
+
+We propose to give in a series of papers an account of the mutant races of
+_Drosophila_ and the linkage shown in their inheritance. In this paper we
+shall consider only the members of the first chromosome, describing a large
+number of new mutants with their linkage relations and summarizing to date
+all the linkage data relating to the first chromosome. In later papers we
+propose to consider the members of the second, third, and fourth
+chromosomes.
+
+The list at the top of page 21 gives the names of the factors dealt with in
+this paper. They stand in the order of their discovery, the mutant forms
+reported here for the first time being starred.
+
+In each experiment the percentage of crossing-over is found by dividing the
+number of the cross-overs by the sum of the non-cross-overs and the
+cross-overs, and multiplying this quotient by 100. The resulting
+percentages, or cross-over values, are used as measures of the distances
+between loci. Thus if the experiments give a cross-over value of 5 per cent
+for white and bifid, we say that white and bifid lie 5 units apart in the X
+chromosome. Other experiments show that yellow and white are about 1 unit
+apart, and that yellow and bifid are about 6 units apart. We can therefore
+construct a diagram with yellow as {21} the zero, with white at 1, and with
+bifid at 6. If we know the cross-over values given by a new mutant with any
+two mutants of the same chromosome whose positions are already determined,
+then we can locate the new factor with accuracy, and be able to predict the
+cross-over value which the new factor will give with any other factor whose
+position is plotted.
+
+_The sex-linked factors of Drosophila._
+
+  +------------+----------+-------+-------+--------+------------+---------+
+  | Gen.       |  Part    |Figure.|Symbol.| Locus. | Date found.|Found by.|
+  |            |affected. |       |       |        |            |         |
+  +------------+----------+-------+-------+--------+------------+---------+
+  |White       |Eye-color | 11    | w     | 1.1    | May 1910   |Morgan.  |
+  |Rudimentary |Wings     | A     | r     | 55.1   | June 1910  |Morgan.  |
+  |Miniature   |Wings     | 7-8   | m     | 36.1   | Aug. 1910  |Morgan.  |
+  |Vermilion   |Eye-color | 10    | v     | 33.0   | Nov. 1910  |Morgan.  |
+  |Yellow      |Body-color| 5     | y     | 0.0    | Jan. 1911  |Wallace. |
+  |Abnormal    |Abdomen   | 4     | A'    | 2.4    | July 1911  |Morgan.  |
+  |Eosin       |Eye-color | 7-8   | w^e   | 1.1    | Aug. 1911  |Morgan.  |
+  |Bifid       |Wings     | B     | b_i   | 6.3    | Nov. 1911  |Morgan.  |
+  |Reduplicated|Legs      |       |       | 34.7   | Nov. 1911  |Hoge.    |
+  |Lethal 1    |Life      |       | l_1   | 0.7    | Feb. 1912  |Rawls.   |
+  |Lethal 1_a_*|Life      |       | l_1a  | 3.3    | Mar. 1912  |Rawls.   |
+  |Spot*       |Body-color| 14-17 | y^s   | 0.0    | April 1912 |Cattell. |
+  |Sable*      |Body-color| 2     | s     | 43.0   | July 1912  |Bridges. |
+  |Dot*        |Thorax    |       |       | 33 +/-   | July 1912  |Bridges.
+      |
+  |Bow*        |Wings     | C     |       |        | Aug. 1912  |Bridges. |
+  |Lemon*      |Body-color| 3     | l_m   | 17.5   | Aug. 1912  |Wallace. |
+  |Lethal 2    |Life      |       | l_2   | 12.5+/-  | Sept. 1912 |Morgan.
+      |
+  |Cherry      |Eye-color | 9     | w^c   | 1.1    | Oct. 1912  |Safir.   |
+  |Fused*      |Venation  | D     | f_u   | 59.5   | Nov. 1912  |Bridges. |
+  |Forked*     |Bristles  | E     | f     | 56.5   | Nov. 1912  |Bridges. |
+  |Shifted*    |Venation  | F     | s_h   | 17.8   | Jan. 1913  |Bridges. |
+  |Lethal sa   |Life      |       | l_sa  | 23.7   | Jan. 1913  |Stark.   |
+  |Bar         |Eye-shape | 12-13 | B'    | 57.0   | Feb. 1913  |Tice.    |
+  |Notch       |Wing      |       | N'    | 2.6    | Mar. 1913  |Dexter.  |
+  |Depressed*  |Wing      | G     | d_p   | 18.0   | April 1913 |Bridges. |
+  |Lethal sb   |Life      |       | l_sb  | 16.7   | April 1913 |Stark.   |
+  |Club*       |Wings     | H     | c_l   | 14.6   | May 1913   |Morgan.  |
+  |Green*      |Body-color|       |       |        | May 1913   |Bridges. |
+  |Chrome*     |Body-color|       |       |        | Sept. 1913 |Bridges. |
+  |Lethal 3    |Life      |       | l_3   | 26.5   | Dec. 1913  |Morgan.  |
+  |Lethal 3_a_ |Life      |       | l_3a  | 19.5   | Jan.  1914 |Morgan.  |
+  |Lethal 1_b_*|Life      |       | l_1b  | 1.1-   | Feb. 1914  |Morgan.  |
+  |Facet*      |Eye       |       | f_a   | 2.2    | Feb.  1914 |Bridges. |
+  |Lethal _sc_ |Life      |       | l_sc  | 66.2   | April 1914 |Stark.   |
+  |Lethal _sd_ |Life      |       | l_sd  |        | May 1914   |Stark.   |
+  |Furrowed    |Eye       |       | f_w   | 38.0   | Nov. 1914  |Duncan.  |
+  +------------+----------+-------+-------+--------+------------+---------+
+
+The factors are located preferably by short distances (_i.e._, by those
+cases in which the amount of crossing-over is small), because when the
+amount of crossing-over is large a correction must be made for double
+crossing-over, and the correction can be best found through breaking up the
+long distances into short ones, by using intermediate points.
+
+Conversely, when a long distance is indicated on the chromosome diagram,
+the actual cross-over value found by experiment (_i.e._, the percentage of
+cross-overs) will be less than the diagram indicates, because the diagram
+has been corrected for double crossing-over. {22}
+
+               0.0 | Yellow, spot
+               0.7 | Lethal I
+               1.1-| Lethal Ib
+               1.1 | White, eosin, cherry
+               2.2 | Facet
+               2.4 | Abnormal
+               2.6 | Notch
+               3.3 | Lethal Ia
+                   |
+               6.3 | Bifid
+                   |
+                   |
+                   |
+                   |
+                   |
+                   |
+              12.5 | Lethal II
+              14.6 | Lethal sb
+              16.7 | Club
+              17.5 | Lemon
+              17.8 | Shifted
+              18.0 | Depressed
+              19.5 | Lethal IIIa
+                   |
+                   |
+              23.7 | Lethal sa
+                   |
+              26.5 | Lethal III
+                   |
+                   |
+                   |
+              33.0 | Vermilion
+              33.+/- | Dot
+              34.7 | Reduplicated
+              36.1 | Miniature
+              38.0 | Furrowed
+                   |
+                   |
+              43.0 | Sable
+                   |
+                   |
+                   |
+                   |
+                   |
+                   |
+              55.1 | Rudimentary
+              56.5 | Forked
+              57.0 | Bar
+              59.5 | Fused
+                   |
+                   |
+                   |
+              66.2 | Lethal sc
+
+              DIAGRAM I.
+
+{23}
+
+Diagram I has been constructed upon the basis of all the data summarized in
+table 65 (p. 84) for the first or X chromosome. It shows the relative
+positions of the gens of the sex-linked characters of _Drosophila_. One
+unit of distance corresponds to 1 per cent of crossing-over. Since all
+distances are corrected for double crossing-over and for coincidence, the
+values represent the _total_ of crossing-over between the loci. The
+uncorrected value obtained in any experiment with two loci widely separated
+will be smaller than the value given in the map.
+
+It may be asked what will happen when two factors whose loci are more than
+50 units apart in the same chromosome are used in the same experiment? One
+might expect to get more than 50 per cent of cross-overs with such an
+experiment, but double crossing-over becomes disproportionately greater the
+longer the distance involved, so that in experiments the observed
+percentage of crossing-over does not rise above 50 per cent. For example,
+if eosin is tested against bar, somewhat under 50 per cent of cross-overs
+are obtained, but if the distance of bar from eosin is found by summation
+of the component distances the interval for eosin bar is 56 units.
+
+In calculating the loci of the first chromosome, a system of weighting was
+used which allowed each case to influence the positions of the loci in
+proportion to the amount of the data. In this way advantage was taken of
+the entire mass of data.
+
+The factors (lethal 1, white, facet, abnormal, notch, and bifid) which lie
+close to yellow were the first to be calculated and plotted. The next step
+was to determine very accurately the position of vermilion with respect to
+yellow. There are many separate experiments which influence this
+calculation and all were proportionately weighted. Then, using vermilion as
+the fixed point the factors (dot, reduplicated, miniature, and sable) which
+lie close to vermilion were plotted. The same process was repeated in
+locating bar with respect to vermilion and the factors about bar with
+reference to bar. The last step was to interpolate the factors (club,
+lethal 2, lemon, depressed, and shifted), which form a group about midway
+between yellow and vermilion. Of these, club is the only one whose location
+is accurate. The apparent closeness of the grouping of these loci is not to
+be taken as significant, for they have been placed only with reference to
+the distant points yellow and vermilion and not with respect to each other;
+furthermore, the data available in the cases of lemon and depressed are
+very meager.
+
+The factors which are most important and are most accurately located are
+yellow, white (eosin), bifid, club, vermilion, miniature, sable, forked,
+and bar. Of these again, white (eosin), vermilion, and bar are of prime
+importance and will probably continue to claim first rank. Of the three
+allelomorphs, white, eosin, and cherry, eosin is the most useful. {24}
+
+NOMENCLATURE.
+
+The system of symbols used in the diagrams and table headings is as
+follows: The factor or gen for a recessive mutant character is represented
+by a lower-case letter, as v for vermilion and m for miniature. The symbols
+for the dominant mutant characters bar, abnormal, and notch are B', A', and
+N'. There are now so many characters that it is impossible to represent all
+of them by a single letter. We therefore add a subletter in such cases, as
+bifid (b_i), fused (f_u), and lethal 2 (l_2). In the case of multiple
+allelomorphs we usually use as the base of the symbol the symbol of that
+member of the system which was first found and add a letter as an exponent
+to indicate the particular member, as y^s for spot, w^e for eosin, and w^c
+for cherry. The normal allelomorphs of the mutant gens are indicated by the
+converse letter, as V for not-vermilion, B_i for not-bifid, and b' for
+not-bar. In the table headings the normal allelomorphs are indicated by
+position alone without the use of a symbol.
+
+Thus the symbol [draw] indicates that the female in question carried eosin,
+not-vermilion, and bar in one chromosome and not-eosin, vermilion, and
+not-bar in the other. The symbol [draw] when used in the heading of a
+column in a table indicates that the flies classified under this heading
+are the result of single crossing-over between eosin and vermilion in a
+mother which was the composition [draw]; the symbol tells at the same time
+that the flies that result from a single cross-over between eosin and
+vermilion in the mother are of the two contrary classes, eosin bar and
+vermilion. When a fly shows two or more non-allelomorphic characters the
+names are written from left to right in the order of their positions from
+the zero end of the map.
+
+       *       *       *       *       *
+
+
+{25}
+
+PART II. NEW DATA.
+
+WHITE.
+
+(Plate II, figure 11.)
+
+The recessive character white eye-color, which appeared in May 1910, was
+the first sex-linked mutation in _Drosophila_ (Morgan, 1910_a_, 1910_b_).
+Soon afterwards (June 1910) rudimentary appeared, and the two types were
+crossed (Morgan, 1910_c_). Under the conditions of culture the viability of
+rudimentary was extremely poor, but the data demonstrated the occurrence of
+recombination of the factors in the ovogenesis so that white and
+rudimentary, though both sex-linked, were brought together into the same
+individual. The results were not fully recognized as linkage, because white
+and rudimentary are so far apart in the chromosome that they seemed to
+assort freely from each other.
+
+Owing to the excellent viability and the perfect sharpness of separation,
+white was extensively used in linkage experiments, especially with
+miniature and yellow (Morgan, 1911_a_; Morgan and Cattell, 1912 and 1913).
+White has been more extensively used than any other character in
+_Drosophila_, though it is now being used very little because of the fact
+that the double recessives of white with other sex-linked eye-colors, such
+as vermilion, are white, and consequently a separation into the true
+genetic classes is impossible. The place of white has been taken by eosin,
+which is an allelomorph of white and which can be readily used with any
+other eye-color.
+
+The locus of white and its allelomorphs is only 1.1 units from that of
+yellow, which is the zero of the chromosome. Yellow and white are very
+closely linked, therefore giving only about one cross-over per 100 flies.
+
+All the published data upon the linkage of white with other sex-linked
+characters have been collected into table 65.
+
+RUDIMENTARY.
+
+Rudimentary, which appeared in June 1910, was the second sex-linked
+character in _Drosophila_ (Morgan, 1910_c_). Its viability has always been
+very poor; in this respect it is one of the very poorest of the sex-linked
+characters. The early linkage data (Morgan, 1911_a_) derived from mass
+cultures have all been discarded. By breeding from a single F_1 female in
+each large culture bottle it has been possible to obtain results which are
+fairly trustworthy (Morgan, 1912_g_; Morgan and Tice, 1914). These data
+appear in table 65, which summarizes all the published data. {26}
+
+The locus of rudimentary is at 55.1, for a long time the extreme right end
+of the known chromosome, though recently several mutants have been found to
+lie somewhat beyond it.
+
+[Illustration: Fig. A. _a._ rudimentary wing; _b._ the wild fly for
+comparison.]
+
+The rudimentary males are perfectly fertile, but the rudimentary females
+rarely produce any offspring at all, and then only a very few. The reason
+for this is that most of the germ-cells cease their development in the
+early growth stage of the eggs (Morgan, 1915_a_).
+
+MINIATURE.
+
+(Plate II. figures 7 and 8.)
+
+The recessive sex-linked mutant miniature wings appeared in August 1910
+(Morgan, 1911b and 1912a). The viability of miniature is fair, and this
+stock has been used in linkage experiments more than any {27} other, with
+the single exception of white. While the wings of miniature usually extend
+backwards, they are sometimes held out at right angles to the body, and
+especially in acid bottles the miniature flies easily become stuck to the
+food or the wings become stringy, so that other wing characters are not
+easy to distinguish in those flies which are also miniature. At present
+vermilion, whose locus is at 33, in being used more frequently in linkage
+work. The locus of miniature at 36.1 is slightly beyond the middle of the
+chromosome.
+
+VERMILION.
+
+(Plate II. figure 10.)
+
+The recessive sex-linked mutant vermilion eye-color (Morgan, 1911_c_ and
+1912_a_) appeared in November 1910, and has appeared at least twice since
+then (Morgan and Plough, 1915). This is one of the best of the sex-linked
+characters, on account of its excellent viability, its sharp distinction
+from normal with very little variability, its value as a double recessive
+in combination with other sex-linked eye-colors, and because of its
+location at 33.0, very near to the middle of the known chromosome.
+
+YELLOW.
+
+(Plate I. figure 5.)
+
+The recessive sex-linked mutant yellow body and wing-color appeared in
+January 1911 (Morgan, 1911_c_ and 1912_a_). Its first appearance was in
+black stock; hence the fly was a double recessive, then called brown. Later
+the same mutation has appeared independently from gray stock. Yellow was
+found to be at the end of the X chromosome, and this end was arbitrarily
+chosen as the zero or the "left end," while the other gens are spoken of as
+lying at various distances to the right of yellow. Recently a lethal gen
+has been located less than one-tenth of a unit (-0.04) to the left of
+yellow, but yellow is still retained as the zero-point.
+
+The viability of yellow is fairly good and the character can be separated
+from gray with great facility, and in consequence yellow has been used
+extensively, although at present it is being used less than formerly, since
+eosin lies only 1.1 units distant from yellow and is generally preferred.
+
+ABNORMAL ABDOMEN.
+
+(Plate I. figure 4.)
+
+The dominant sex-linked character abnormal abdomen appeared in July 1911
+(Morgan, 1911_d_). It was soon found that the realization of the abnormal
+condition depended greatly upon the nature of the environment (Morgan,
+1912). Recently a very extensive study of this character has been published
+(Morgan, 1915). As this case has been reviewed in the introduction, there
+is little further to be said here. {28} Because of the change that takes
+place as the culture grows older (the abnormal changing to normal), this
+character is not of much value in linkage work. The location of the factor
+in the X chromosome at 2.4 has been made out from the data given by Morgan
+(1915_b_). These data, which in general include only the abnormal classes,
+are summarized in table 1.
+
+TABLE 1.--_Linkage data, from Morgan, 1915b._
+
+  +------------------+-----------+-----------+------------+
+  |     Gens.        |  Total.   |   Cross-  | Cross-over |
+  |                  |           |   overs.  |  values.   |
+  +------------------+-----------+-----------+------------+
+  | Yellow white     |  28,018   |    334    |    1.2     |
+  | Yellow abnormal  |  15,314   |    299    |    2.0     |
+  | White abnormal   |  16,300   |    277    |    1.7     |
+  +------------------+-----------+-----------+------------+
+
+EOSIN.
+
+(Plate II, figures 7 and 8.)
+
+The recessive sex-linked mutation eosin eye-color appeared in August 1911
+in a culture of white-eyed flies (Morgan 1912_a_). The eye-color is
+different in the male and female, the male being a light pinkish yellow,
+while the female is a rather dark yellowish pink. Eosin is allelomorphic to
+white and the white-eosin compound or heterozygote has the color of the
+eosin male. There is probably no special significance in this coincidence
+of color, since similar dilutions to various degrees have been demonstrated
+for all the other eye-colors tested (Morgan and Bridges, 1913). Since eosin
+is allelomorphic to white, its locus is also at 1.1. Eosin is the most
+useful character among all those in the left end of the chromosome.
+
+BIFID.
+
+The sex-linked wing mutant bifid, which appeared in November 1911, is
+characterized by the fusion of all the longitudinal veins into a heavy
+stalk at the base of the wing. The wing stands out from the body at a wide
+angle, so that the fusion is easily seen. At the tip of the wing the third
+longitudinal vein spreads out into a delta which reaches to the marginal
+vein. The fourth longitudinal vein reaches the margin only rarely. There is
+very often opposite this vein a great bay in the margin, or the whole wing
+is irregularly truncated.
+
+The stock of bifid was at first extremely varied in the amount of this
+truncation. By selection a stock was secured which showed only very greatly
+reduced wings like those shown in figures _a_, b. Another stock (figs. _c_,
+_d_) was secured by outcrossing and selection which showed wings of nearly
+normal size and shape, which always had the bifid stalk, generally the
+spread positions (not as extreme), and often the delta and the shortened
+fourth longitudinal vein. We believe that the extreme reduction in size
+seen in the one stock was due to an added modifier of {29} the nature of
+beaded, since this could be eliminated by outcrossing and selection.
+
+[Illustration: FIG. B.--Bifid wing. _c_ and _d_ show the typical condition
+of bifid wings. All the longitudinal veins are fused into a heavy stalk at
+the base of the wing. _a_ shows the typical position in which the bifid
+wings are held. The small size of the wings in _a_ and _b_ is due to the
+action of a modifier of the nature of "beaded" which has been eliminated in
+_c_, d.]
+
+LINKAGE OF BIFID WITH YELLOW, WITH WHITE, AND WITH VERMILION.
+
+The stock of the normal (not-beaded) bifid was used by Dr. R. Chambers,
+Jr., for determining the chromosome locus of bifid by means of its linkage
+relations to vermilion, white, and yellow (Chambers, 1913). We have
+attempted to bring together in table 2 the complete data and to calculate
+the locus of bifid.
+
+TABLE 2.--_Linkage data, from Chambers, 1913._
+
+  +-----------------+------------+-------------+--------------+
+  |      Gens.      |   Total.   |    Cross-   |  Cross-over  |
+  |                 |            |    overs.   |   values.    |
+  +-----------------+------------+-------------+--------------+
+  | Yellow bifid    |    3,175   |      182    |     5.8      |
+  | White bifid     |   20,800   |    1,127    |     5.3      |
+  | Bifid vermilion |    2,509   |      806    |    32.1      |
+  +-----------------+------------+-------------+--------------+
+
+{30}
+
+In the crosses between white and bifid there were 1,127 cross-overs in a
+total of 20,800 available individuals, which gives a cross-over value of
+5.3. In the crosses between yellow and bifid there were 182 cross-overs in
+a total of 3,175 available individuals, which gives a cross-over value of
+5.8. In crosses between bifid and vermilion there were 806 cross-overs in a
+total of 2,509, which gives a cross-over value of 32.1. On the basis of all
+the data summarized in table 65, bifid is located at 6.3 to the right of
+yellow.
+
+LINKAGE OF CHERRY, BIFID, AND VERMILION.
+
+In a small experiment of our own, three factors were involved--cherry,
+bifid, and vermilion. A cherry vermilion female was crossed to a bifid
+male. Two daughters were back-crossed singly to white bifid males. The
+female offspring will then give data for the linkage of cherry white with
+bifid, while the sons will show the linkage of the three gens, cherry,
+bifid, and vermilion. The results are shown in table 3.
+
+TABLE 3.--_P_1 cherry vermilion [female] [female] x bifid [male] [male]. B.
+C.[2] F_1 wild-type [female] x white bifid [male] [male]._
+
+  |-----------------------------------
+  |      |       F_2 females.        |
+  |      |---------------------------+
+  |      |                           |
+  |Refer-| Non-cross-  |Cross-overs. |
+  |ence. |   overs.    |             |
+  |      |-------------+-------------+
+  |      |White-|Bifid.|White-|Wild- ~
+  |      |cherry|      |cherry|type. ~
+  |      |      |      |bifid.|      |
+  |------+------+------+------+------+
+  |  262 |   40 |   46 |   1  |   2  |
+  |  263 |   47 |   45 |   3  |   3  |
+  |      |------+------+------+------+
+  |Total.|   87 |   91 |   4  |   5  |
+  |-----------------------------------
+
+  |----------------------------------------------------------------------|
+  |      |                         F_2 males.                            |
+  |      |-----------------------------+---------------------------------|
+  |      | w^c        v | w^c b        | w^c           |  w^c  b_i   v   |
+  |Refer-| ------------ | ---+-------- | ---------+--- |  ---+-----+---  |
+  |ence. |     b_i      |           v  |     b_i    v  |                 |
+  |      |--------------+--------------+---------------+-----------------|
+  ~      |Cherry |Bifid.|Cherry| Ver-  |Cherry.|Bifid  | Cherry   |Wild- |
+  ~      | ver-  |      |bifid.|milion.|       | ver-  |  bifid   |type. |
+  |      |milion.|      |      |       |       |milion.|vermilion.|      |
+  |------+-------+------+------+-------+-------+-------+----------+------|
+  |  262 |  45   |  38  |   3  |   2   |   11  |   13  |     ..   |  ..  |
+  |  263 |  30   |  50  |   1  |   3   |    8  |   10  |      1   |  ..  |
+  |      |-------+------+------+-------+-------+-------+----------+------|
+  |Total.|  75   |  88  |   4  |   5   |   19  |   23  |      1   |   0  |
+  |----------------------------------------------------------------------|
+
+Both males and females give a cross-over value of 5 units for cherry bifid,
+which is the value determined by Chambers. The order of the factors, viz,
+cherry, bifid, vermilion, is established by taking advantage of the double
+cross-over classes in the males. The male classes give a cross-over value
+of 20 for bifid vermilion and 24 for cherry vermilion, which are low
+compared with values given by other experiments. The locus of bifid at 6.3
+is convenient for many linkage problems, but this advantage is largely
+offset by the liability of the bifid flies to become stuck in the food and
+against the sides of the bottle. Bifid flies can be separated from the
+normal with certainty and with great ease. {31}
+
+REDUPLICATED LEGS.
+
+In November 1912 Miss Mildred Hoge found that a certain stock was giving
+some males whose legs were reduplicated, either completely or only with
+respect to the terminal segments (described and figured, Hoge, 1915).
+Subsequent work by Miss Hoge showed that the condition was due to a
+sex-linked gen, but that at room temperature not all the flies that were
+genetically reduplicated showed reduplication. However, if the flies were
+raised through the pupa stage in the ice-box at a temperature of about
+10deg to 12deg a majority of the flies which were expected to show
+reduplication did so. The most extremely reduplicated individual showed
+parts of 14 legs.
+
+In studying the cross-over values of reduplicated, only those flies that
+have abnormal legs are to be used in calculation, as in the case of
+abnormal abdomen where the phenotypically normal individuals are partly
+genetically abnormal. Table 4 gives a summary of the data secured by Miss
+Hoge.
+
+TABLE 4.--_Summary of linkage data upon reduplicated legs, from Hoge,
+1915._
+
+  +---------------------------+---------+---------+------------+
+  |         Gens.             |  Total. |  Cross- | Cross-over |
+  |                           |         |  overs. |  values.   |
+  |---------------------------+---------+---------|------------|
+  |                           |         |         |            |
+  |White reduplicated         |    418  |   121   |    29.0    |
+  |Reduplicated vermilion     |    667  |    11   |     1.7    |
+  |Reduplicated bar           |    583  |   120   |    20.6    |
+  |                           |         |         |            |
+  +---------------------------+---------+---------+------------+
+
+The most accurate data, those upon the value for reduplicated and
+vermilion, give for reduplicated a distance of 1.7 from vermilion, either
+to the right or to the left. The distance from white is 29, which would
+place the locus for reduplication to the left of vermilion, which is at 33.
+The data for bar give a distance of 21, but since bar is itself 24 units
+from vermilion, this distance of 21 would seem to place the locus to the
+right of vermilion. The evidence is slightly in favor of this position to
+the right of vermilion at 34.7, where reduplicated may be located
+provisionally. In any case the locus is so near to that of vermilion that
+final decision must come from data involving double crossing-over, _i. e._,
+from a three-locus experiment.
+
+LETHAL 1.
+
+In February 1912 Miss E. Rawls found that certain females from a wild stock
+were giving only about half as many sons as daughters. Tests continuing
+through five generations showed that the sons that appeared were entirely
+normal, but that half of the daughters gave again 2 : 1 sex-ratios, while
+the other half gave normal 1 : 1 sex-ratios. {32}
+
+The explanation of this mode of transmission became clear when it was found
+that the cause of the death of half of the males was a particular factor
+that had as definite a locus in the X chromosome as have other sex-linked
+factors (Morgan, 1912_e_). Morgan mated females (from the stock sent to him
+by Miss Rawls) to white-eyed males. Half of the females, as expected, gave
+2 : 1 sex-ratios, and daughters from these were again mated to white males.
+Here once more half of the daughters gave 2 : 1 sex-ratios, but in such
+cases the sons were nearly all white-eyed and only rarely a red-eyed son
+appeared, when under ordinary circumstances there should be just as many
+red sons as white sons. The total output for 11 such females was as follows
+(Morgan, 1914_b_): white [female], 457; red [female], 433; white [male],
+370; red [male], 2. It is evident from these data that there must be
+present in the sex-chromosome a gen that causes the death of every male
+that receives this chromosome, and that this lethal factor lies very close
+to the factor for white eyes. The linkage of this lethal (now called lethal
+1) to various other sex-linked gens was determined (Morgan 1914_b_), and is
+summarized in table 5. On the basis of these data it is found that the gen
+lethal 1 lies 0.4 unit to the left of white, or at 0.7.
+
+TABLE 5.--_Summary of linkage data upon lethal 1, from Morgan, 1914b, pp.
+81-92._
+
+  +------------------------+---------+--------+-------------+
+  |          Gens.         |  Total. | Cross- |  Cross-over |
+  |                        |         | overs. |   values.   |
+  +------------------------+---------+--------+-------------+
+  |                        |         |        |             |
+  | Yellow lethal 1        |    131  |    1   |     0.8     |
+  | Yellow miniature       |    131  |   45   |    34.4     |
+  | Lethal 1 white         |  1,763  |    7   |     0.4     |
+  | Lethal 1 miniature     |    814  |  323   |    39.7     |
+  | White miniature        |    994  |  397   |    39.9     |
+  |                        |         |        |             |
+  +------------------------+---------+--------+-------------+
+
+LETHAL 1a.
+
+In the second generation of the flies bred by Miss Rawls, one female gave
+(March 1912) only 3 sons, although she gave 312 daughters. It was not known
+for some time (see lethals 3 and 3_a_) what was the cause of this extreme
+rarity of sons. It is now apparent, however, that this mother carried
+lethal 1 in one X and in the other X a new lethal which had arisen by
+mutation. The new lethal was very close to lethal 1, as shown by the rarity
+of the surviving sons, which are cross-overs between lethal 1 and the new
+lethal that we may call lethal 1a. There is another class of cross-overs,
+namely, those which have lethal 1 and get lethal 1_a_ by crossing-over.
+These doubly lethal males must also die, but since they are theoretically
+as numerous as the males (3) free from both lethals, we must double this
+number (3 x 2) to get the total number of cross-overs. There were 312
+daughters, but as the sons are normally about 96 per cent of the number of
+the females, {33} we may take 300 as the number of the males which died.
+There must have been, then, about 2 per cent of crossing-over, which makes
+lethal 1_a_ lie about 2 units from lethal 1. This location of lethal 1_a_
+is confirmed by a test that Miss Rawls made of the daughters of the
+high-ratio female. Out of 98 of these daughters none repeated the high
+sex-ratio and only 2 gave 1 [female] : 1 [male] ratios. The two daughters
+which gave 1 : 1 ratios are cross-overs. There should be an equal number of
+cross-overs which contain both lethals. These latter would not be
+distinguishable from the non-cross-over females, each of which carries one
+or the other lethal. In calculation, allowance can be made for them by
+doubling the number of observed cross-overs (2 x 2) and taking 98 - 2 as
+the number of non-cross-overs. The cross-over fraction {6 + 4}/{300 + 96}
+gives 2.6 as the distance between the two lethals. Lethal 1_a_ is probably
+to the right of lethal 1 at 0.7 + 2.6 = 3.3.
+
+SPOT.
+
+(Plate II, figures 14 to 17.)
+
+In April 1912 there was found in the stock of yellow flies a male that
+differed from yellow in that it had a conspicuous light spot on the upper
+surface of the abdomen (Morgan, 1914_a_). In yellow flies this region is
+dark brown in color. In crosses with wild flies the spot remained with the
+yellow, and although some 30,000 flies were raised, none of the gray
+offspring showed the spot, which should have occurred had crossing-over
+taken place. The most probable interpretation of spot is that it was due to
+another mutation in the yellow factor, the first mutation being from gray
+to yellow and the second from yellow to spot.
+
+Spot behaves as an allelomorph to yellow in all crosses where the two are
+involved and is completely recessive to yellow, _i. e._, the yellow-spot
+hybrid is exactly like yellow. A yellow-spot female, back-crossed to a spot
+male, produces yellows and spots in equal numbers.
+
+In a cross of spot to black it was found that the double recessive, spot
+black, flies that appear in F_2 have, in addition to the spot on the
+abdomen, another spot on the scutellum and a light streak on the thorax.
+These two latter characters ("dot and dash") are very sharply marked and
+conspicuous when the flies are young, but they are only juvenile characters
+and disappear as the flies become older. The spot flies never show the "dot
+and dash" clearly, and it only comes out when black acts as a developer.
+These characters furnish a good illustration of the fact that mutant gens
+ordinarily affect many parts of the body, though these secondary effects
+often pass unnoticed.
+
+In the F_2 of the cross of spot by black one yellow black fly appeared,
+although none are expected, on the assumption that spot and yellow {34} are
+allelomorphic. Unless due to crossing-over it must have been a mutation
+from spot back to yellow. Improbable as this may seem to those who look
+upon mutations as due to losses from the germ-plasm, yet we have records of
+several other cases where similar mutations "backwards" have taken place,
+notably in the case of eosin to white, under conditions where the
+alternative interpretation of crossing-over is excluded.
+
+SABLE.
+
+(Plate I, figure 2.)
+
+In an experiment involving black body-color[3] a fly appeared (July 19,
+1912) whose body-color differed slightly from ordinary black in that the
+trident mark on the thorax was sharper and the color itself was brighter
+and clearer. This fly, a male, was mated to black females and gave some
+black males and females, but also some gray (wild body-color) males and
+females, showing not only that he was heterozygous for ordinary recessive
+black, but at the same time that his dark color must be due to another kind
+of black. The gray F_1 flies when mated together gave a series of gray and
+dark flies in F_2 about as follows: In the females 3 grays to 1 dark; in
+the males 3 grays to 5 dark in color. The result indicated that the new
+black color, which we call sable, was due to a sex-linked factor. It was
+difficult to discover which of the heterogeneous F_2 males were the new
+blacks. Suspected males were bred (singly) to wild females, and the F_2
+dark males, from those cultures that gave the closest approach to a 2 gray
+[female] : 1 gray [male] : 1 dark [male], were bred to their sisters in
+pairs in order to obtain sable females and males. Thus stock homozygous for
+sable but still containing black as an impurity was obtained. It became
+necessary to free it from black by successive individual out-crossings to
+wild flies and extractions.
+
+This account of how sable was purified shows how difficult it is to
+separate two recessive factors that give closely similar somatic effects.
+If a character like sable should be present in any other black stock, or if
+a character like black should be present in sable, very erratic results
+would be obtained if such stocks were used in experiments, before such a
+population had been separated into its component races.
+
+Sable males of the purified stock were mated to wild females and gave
+wild-type (gray) males and females. These inbred gave the results shown in
+table 6.
+
+No sable females appeared in F_2, as seen in table 6. The reciprocal cross
+gave the results shown in table 7.
+
+{35}
+
+The F_1 males were sable like their mother. The evidence thus shows that
+sable is a sex-linked recessive character. Our next step was to determine
+the linkage relations of sable to certain other sex-linked gens, namely,
+yellow, eosin, cherry, vermilion, miniature, and bar.
+
+TABLE 6.--_P_1 wild [female] [female] x sable [male]. F_1 wild-type
+[female] [female] x F_1 wild-type [male] [male]._
+
+  +---------------+-------------------+-------------------+---------------+
+  |               |                   |                   |               |
+  | Reference.[4] |Wild-type [female].| Wild-type [male]. | Sable [male]. |
+  |               |                   |                   |               |
+  +---------------+-------------------+-------------------+---------------+
+  |               |                   |                   |               |
+  |     88 C      |        218        |       100         |       70      |
+  |    143 C      |        245        |       108         |       72      |
+  |    146 C      |        200        |       115         |       82      |
+  |               +-------------------+-------------------+---------------+
+  |        Total  |        663        |       323         |      224      |
+  |               |                   |                   |               |
+  +---------------+-------------------+-------------------+---------------+
+
+TABLE 7.--_P_1 sable [female] x wild [male] [male]. F_1 wild-type [female]
+x F_1 sable [male]._
+
+  +--------------+-------------+-------------+-------------+-------------+
+  |              |             |             |             |             |
+  | Reference.   | Wild-type   | Wild-type   |  Sable      |   Sable     |
+  |              |  [female].  |  [male].    | [female].   |   [male].   |
+  +--------------+-------------+-------------+-------------+-------------+
+  |              |             |             |             |             |
+  |       4 I    |      10     |      10     |     6       |     10      |
+  |              |             |             |             |             |
+  +--------------+-------------+-------------+-------------+-------------+
+
+LINKAGE OF YELLOW AND SABLE.
+
+The factor for yellow body-color lies at one end of the known series of
+sex-linked gens. As already stated, we speak of this end as the left end of
+the diagram, and yellow as the zero in locating factors.
+
+When yellow (not-sable) females were mated to (not-yellow) sable males they
+gave wild-type (gray) daughters and yellow sons. These inbred gave in F_2
+two classes of females, namely, yellow and gray, and four classes of males,
+namely, yellow and sable (non-cross-overs), wild type and the double
+recessive yellow sable (cross-overs). From off-spring (F_3) of the F_2
+yellow sable males by F_2 yellow females, pure stock of the double
+recessive yellow sable was made up and used in the crosses to test linkage.
+
+In color the yellow sable is quite similar to yellow black, that is, a rich
+brown with a very dark brown trident pattern on the thorax. Yellow sable is
+easier to distinguish from yellow than is yellow black, even when the flies
+have not yet acquired their adult body-color.
+
+Yellow sable males were bred to wild females and F_1 consisted of wild-type
+males and females. These inbred gave the results shown in table 8. {36}
+
+TABLE 8.--_P_1 wild [female] [female] x yellow sable [male] [male]. F_1
+wild-type [female] [female] x F_1 wild-type [male] [male]._
+
+  +-----------+---------+--------------+--------------+-------+-----------+
+  |           |         |Non-cross-over|  Cross-over  |       |           |
+  |           |  Wild-  |    [male].   |    [male].   |       |           |
+  | Reference.|  type   +-------+------+-------+------+ Total |Cross-over |
+  |           |[female].| Yellow| Wild-|       |      | males.|  value.   |
+  |           |         | sable.| type.|Yellow.|Sable.|       |           |
+  +-----------+---------+-------+------+-------+------+-------+-----------+
+  |           |         |       |      |       |      |       |           |
+  |    44 I   |    292  |  110  |   43 |   75  |  36  |  264  |     42    |
+  |    45 I   |    384  |  104  |   58 |   71  |  60  |  293  |     45    |
+  |           +---------+--------------+-------+------+-------+-----------+
+  |    Total  |    676  |  214  |  101 |  146  |  96  |  557  |     43    |
+  |           |         |       |      |       |      |       |           |
+  +-----------+---------+-------+------+-------+------+-------+-----------+
+
+Some of the F_1 females were back-crossed to yellow sable males and gave
+the data for table 9.
+
+TABLE 9.--_P_1 wild-type [female] [female] x yellow sable [male] [male]. B.
+C. F_1 wild-type [female] x yellow sable [male] [male]._
+
+  +----------+-------------------------+---------------+-------+----------+
+  |          |                         |               |       |          |
+  |          |     Non-cross-overs.    |  Cross-overs. |       |          |
+  |          |                         |               |       |          |
+  |Reference.+-----------+-------------+-------+-------+ Total.|Cross-over|
+  |          |           |             |       |       |       |  value.  |
+  |          | Wild-type.|Yellow sable.|Yellow.| Sable.|       |          |
+  |          |           |             |       |       |       |          |
+  +----------+-----------+-------------+-------+-------+-------+----------+
+  |          |           |             |       |       |       |          |
+  |  31 I    |    108    |      51     |   58  |   56  |   273 |    42    |
+  |  49 I    |    265    |     175     |  161  |  169  |   770 |    43    |
+  |          +-----------+-------------+-------+-------+-------+----------+
+  |    Total |    373    |     226     |  219  |  225  | 1,043 |    43    |
+  |          |           |             |       |       |       |          |
+  +----------+-----------+-------------+-------+-------+-------+----------+
+
+In these tables the last column (to the right) shows for each culture the
+amount of crossing-over between yellow and sable. These values are found by
+dividing the number of cross-overs by the total number of individuals which
+might show crossing-over, that is, males only or both males and females, as
+the case may be. Free assortment would give 50 per cent of cross-overs and
+absolute linkage 0 per cent of cross-overs. Except where the percentage of
+crossing-over is very small these values are expressed to the nearest unit,
+since the experimental error might make a closer calculation misleading.
+
+The combined data of tables 8 and 9 give 686 cross-overs in a total of
+1,600 individuals in which crossing-over might occur. The females of table
+8 are all of one class (wild type) and are useless for this calculation
+except as a check upon viability. The cross-over value of 43 per cent shows
+that crossing-over is very free. We interpret this to mean that sable is
+far from yellow in the chromosome. Since yellow is at one end of the known
+series, sable would then occupy a locus somewhere near the opposite end.
+This can be checked up by finding its linkage relations to the other
+sex-linked factors. {37}
+
+LINKAGE OF CHERRY AND SABLE.
+
+The origin of cherry eye-color (Plate II, fig. 9) has been given by Safir
+(Biol. Bull., 1913). From considerations which will be discussed later in
+this paper we regard cherry as allelomorphic to white in a quadruple
+allelomorph system composed of white, eosin, cherry, and their normal red
+allelomorph. Cherry will then occupy the same locus as white, which is one
+unit to the right of yellow, and will show the same linkage relations to
+other factors as does white. A slightly lower cross-over value should be
+given by cherry and sable than was given by yellow and sable.
+
+When cherry (gray) females were crossed to (red) sable males the daughters
+were wild type and the sons cherry. Inbred these gave the results shown in
+table 10.
+
+TABLE 10.--_P_1 cherry [female][female] x sable [male][male]. F_1 wild-type
+[female] x F_1 cherry [male] [male]._
+
+  +---------+---------+---------+--------------+------------+------+------+
+  |         |         |         |  Non-cross-  | Cross-over |      |      |
+  |         |  Wild-  | Cherry  | over [male]. |   [male].  |      |Cross-|
+  |  Refer- |  type   |[female].+-------+------+------+-----+Total | over |
+  |  ence.  |[female].|         |Cherry.|Sable.|Cherry|Wild-|males.|value.|
+  |         |         |         |       |      |sable.|type.|      |      |
+  +---------+---------+---------+-------+------+------+-----+------+------+
+  |         |         |         |       |      |      |     |      |      |
+  | 24  I   |    94   |   105   |   51  |   42 |  20  |  43 |  156 |  40  |
+  | 55  I   |   101   |   131   |   63  |   52 |  38  |  48 |  201 |  43  |
+  | 55' I   |    96   |    94   |   52  |   31 |  29  |  30 |  142 |  42  |
+  |         +---------+---------+-------+------+------+-----+------+------+
+  | Total   |   291   |   330   |  166  |  125 |  87  | 121 |  499 |  42  |
+  |         |         |         |       |      |      |     |      |      |
+  +---------+---------+---------+-------+------+------+-----+------+------+
+
+The percentage of crossing-over between cherry and sable is 42. Since
+cherry is one point from yellow, this result agrees extremely well with the
+value 43 for yellow and sable. Since yellow and eosin lie at the left end
+of the first chromosome, the high values, namely, 43 and 42, agree in
+making it very probable that sable lies near the other end (_i. e._, to the
+right). Sable will lie farther to the right than vermilion, for vermilion
+has been shown elsewhere to give 33 per cent of crossing-over with eosin.
+The location of sable to the right of vermilion has in fact been
+substantiated by all later work.
+
+LINKAGE OF EOSIN, VERMILION, AND SABLE.
+
+Three loci are involved in the next experiment. Since eosin is an
+allelomorph of cherry, it should be expected to give with sable the same
+cross-over value as did cherry. When eosin (red) sable females were crossed
+to (red) vermilion (gray) males, the daughters were wild type and the males
+were eosin sable. Inbred these gave the classes shown in table 11. {38}
+
+TABLE 11.--_P_1 eosin sable [female] x vermilion [male][male]. F_1
+wild-type [female][female] x F_1 eosin sable [male][male]._
+
+  +------+--------------------------+
+  |      |                          |
+  |      |       F_2 females.       |
+  |      |                          |
+  |      +------------+-------------+
+  |      | w^e      s | w^e         |
+  |Refer-| ---------- | -----+----- |
+  |      |            |           s |
+  |ence. +------+-----+------+------+
+  |      |      |     |      |      |
+  |      |      |     |      |      |
+  |      |Eosin |Wild-|Eosin.|Sable.~
+  |      |sable.|type.|      |      ~
+  |      |      |     |      |      |
+  +------+------+-----+------+------+
+  |      |      |     |      |      |
+  | 26 I | 132  | 171 |  113 |  109 |
+  | 26'I |  96  | 146 |   86 |   78 |
+  |      +------+-----+------+------+
+  |Total.| 228  | 317 |  199 |  187 |
+  +------+------+-----+------+------+
+
+  +------+---------------------------------------------------------+
+  |      |                                                         |
+  |      |                         F_2 males.                      |
+  |      |                                                         |
+  |      +---------------+--------------+-------------+------------+
+  |      | w^e       s   | w^e    v     | w^e         | w^e  v   s |
+  |Refer-| -----------   | -----+-----  | --------+-- | ---+---+-- |
+  |      |        v      |           s  |       v   s |            |
+  |ence. +-------+-------+-------+------+------+------+------+-----+
+  |      |       |       |       |      |      |      |      |     |
+  |      |       |       |Eosin  |      |      |Ver-  |Eosin |     |
+  ~      | Eosin |Ver-   |ver-   |Sable.|Eosin.|milion|ver-  |Wild-|
+  ~      | sable.|milion.|milion.|      |      |sable.|milion|type.|
+  |      |       |       |       |      |      |      |sable.|     |
+  +------+-------+-------+-------+------+------+------+------+-----+
+  |      |       |       |       |      |      |      |      |     |
+  | 26 I |  127  |  163  |  75   |  76  |   37 |  14  |   2  |  5  |
+  | 26'I |   74  |  128  |  76   |  59  |   18 |  21  |   4  |  3  |
+  |      +-------+-------+-------+------+------+------+------+-----+
+  |Total.|  201  |  291  | 151   | 135  |   55 |  35  |   6  |  8  |
+  +------+-------+-------+-------+------+------+------+------+-----+
+
+If we consider the male classes of table 11, we find that the smallest
+classes are eosin vermilion sable and wild type, which are the expected
+double cross-over classes if sable lies to the right of vermilion, as
+indicated by the crosses with eosin and with yellow. The classes which
+represent single crossing-over between eosin and vermilion are eosin
+vermilion, and sable, and those which represent single crossing-over
+between vermilion and sable are eosin and vermilion sable. These relations
+are seen in diagram II.
+
+    w^e                                                V              s
+  --+--------------------------------------------------+--------------+
+                                     X                         X
+  --+--------------------------------------------------+--------------+
+    W                                                  v              S
+
+DIAGRAM II.--The upper line represents an X chromosome, the lower line its
+mate. The cross connecting lines indicate crossing-over between pairs of
+factors.
+
+                      w^e                      s   {Eosin sable.
+  Non-cross-overs     --------------------------   {
+                                         v         {Vermilion.
+
+                      w^e                v         {Eosin vermilion.
+  Single cross-overs  ------------+-------------   {
+                                               s   {Sable.
+
+                      w                            {Eosin.
+                      -----------------------+--   {
+                                         v     s   {Vermilion sable.
+
+                      w^e                v     s   {Eosin vermilion sable.
+  Double cross-overs  ------------+----------+--   {
+                                                   {Wild-type.
+
+If we consider the female classes of table 11, we get information as to the
+cross-over value of eosin and sable, namely, 42 units. The male classes
+will be considered in connection with the cross that follows.
+
+The next experiment involves the same three gens which now enter in
+different relations. A double recessive, eosin vermilion (gray) female {39}
+was mated to (red red) sable males and gave 202 wild-type[5] females and
+184 eosin vermilion males. Two F_1 pairs gave the results shown in table 12
+(the four classes of females not being separated).
+
+TABLE 12.--_P_1 eosin vermilion F_1 wild-type [female] x F_1 eosin
+vermilion [male] [male]._
+
+  +------+--------+-------------------------------------------------------+
+  |      |        |                        F_2 males.                     |
+  |      |        +-------------+-------------+-------------+-------------+
+  |      |        | w^e   v     | w^e       s | w^e   v   s | w^e         |
+  |      |        | ----------- | -----+----- | --------+-- | ----+---+-- |
+  |Refer-| F_2    |           s |         v   |             |       v   s |
+  | ence.|females.+------+------+------+------+------+------+------+------+
+  |      |        |      |      |      |      |Eosin |      |      |      |
+  |      |        |Eosin |      |      |      |verm- |Wild- |      |Verm- |
+  |      |        |verm- |Sable.|Eosin |Verm- |ilion |type. |Eosin.|ilion |
+  |      |        |ilion.|[male]|sable.|ilion.|sable.|[male]|[male]|sable.|
+  |      |        |[male]|      |[male]|[male]|[male]|      |      |[male]|
+  +------+--------+------+------+------+------+------+------+------+------+
+  | 59 C |   133  |  40  |  33  |   7  |  16  |   5  |   5  |   2  |   1  |
+  | 61 C |   101  |  34  |  26  |   8  |  11  |   3  |   7  |   1  |   0  |
+  |      +--------+------+------+------+------+------+------+------+------+
+  |Total |   234  |  74  |  59  |  15  |  27  |   8  |  12  |   3  |   1  |
+  +------+--------+------+------+------+------+------+------+------+------+
+
+If we combine the data for males given in table 12 with those of table 11,
+we get the following cross-over values. Eosin vermilion, 32; vermilion
+sable, 12; eosin sable, 41.
+
+{40}
+
+LINKAGE OF MINIATURE AND SABLE.
+
+The miniature wing has been described (Morgan, Science, 1911) and the wing
+figured (Morgan, Jour. Exp. Zool., 1911). The gen for miniature lies about
+3 units to the right of vermilion, so that it is still closer to sable than
+is vermilion. The double recessive, miniature sable, was made up, and males
+of this stock were bred to wild females (long gray). The wild-type
+daughters were back-crossed to double recessive males and gave the results
+(mass cultures) shown in table 13.
+
+TABLE 13.--_P_1 wild [female] [female] x miniature sable [male] [male]. B.
+C. F_1 wild-type [female] [female] x miniature sable [male] [male]._
+
+  +-----------+---------------------+-----------------+-------+-------+
+  |           |                     |                 |       |       |
+  |           |   Non-cross-overs.  |  Cross-overs.   |       |       |
+  |           |                     |                 |       | Cross-|
+  | Reference.+----------+----------+----------+------+ Total.|  over |
+  |           |          |          |          |      |       | value.|
+  |           |Miniature |Wild-type.|Miniature.|Sable.|       |       |
+  |           |  sable.  |          |          |      |       |       |
+  +-----------+----------+----------+----------+------+-------+-------+
+  |           |          |          |          |      |       |       |
+  |  38 I     |    245   |    283   |    15    |  17  |   560 |   6   |
+  |  43 I     |    191   |    236   |    13    |  18  |   458 |   7   |
+  |  46 I     |    232   |    274   |    24    |  21  |   551 |   8   |
+  |           +----------+----------+----------+------+-------+-------+
+  |   Total   |    668   |    793   |    52    |  56  | 1,569 |   7   |
+  |           |          |          |          |      |       |       |
+  +-----------+----------+----------+----------+------+-------+-------+
+
+Since the results for the male and the female classes are expected to be
+the same, the sexes were not separated. The combined data give 7 per cent
+of crossing-over between miniature and sable.
+
+LINKAGE OF VERMILION, SABLE, AND BAR.
+
+Bar eye has been described by Mrs. S. C. Tice (1914). It is a dominant
+sex-linked character, whose locus, lying beyond vermilion and sable, is
+near the right end of the chromosome series, that is, at the end opposite
+yellow.
+
+In the first cross of a balanced series of experiments for the gens
+vermilion, sable, and bar, vermilion (gray not-bar) entered from one side
+([female]) and (red) sable bar from the other ([male]). The daughters were
+bar and the sons vermilion. The daughters were back-crossed singly to the
+triple recessive males vermilion sable (not-bar), and gave the data
+included in table 14.
+
+In the second cross, vermilion sable (not-bar) went in from one side
+([female]) and (red, gray) bar from the other. The daughters were bar and
+the sons were vermilion sable. Since these sons have the three recessive
+factors, inbreeding of F_1 is equivalent to a triple back-cross. The
+results are given by pairs in table 15. {41}
+
+TABLE 14.--_P_1 vermilion [female] [female] x sable bar [male] [male]. B.
+C. F_1 bar [female] x vermilion sable [male] [male]._
+
+  +------+------------+-----------+------------+-----------+
+  |      | v          | v    s B' | v       B' | v   s     |
+  |      | ---------- | ---+----- | -----+---- | --+--+--- |
+  |      |    s    B' |           |     s      |        B' |
+  |      +------+-----+-----+-----+-----+------+------+----+
+  |Refer-|      |     |Verm-|     |     |      |      |    |
+  |ence. |Verm- |Sable|ilion|Wild-|Verm-|      |Ver-  |    |
+  |      |ilion.| bar.|sable|type.|ilion|Sable.|milion|Bar.|
+  |      |      |     | bar.|     | bar.|      |sable.|    |
+  +------+------+-----+-----+-----+-----+------+------+----+
+  |      |      |     |     |     |     |      |      |    |
+  |147 I |   81 |  66 |  12 |  15 |  15 |  18  |      |    ~
+  |148 I |  103 | 108 |   4 |  19 |  11 |  11  |      |    ~
+  |149 I |   97 |  88 |  10 |   8 |  17 |  17  |   1  |  1 |
+  |150 I |   95 |  75 |  10 |  11 |  21 |  22  |   1  |  1 |
+  |151 I |  116 |  96 |  11 |  15 |  23 |  26  |      |  2 |
+  | 89   |   89 |  94 |  10 |  19 |  15 |  11  |   1  |    |
+  | 90   |   49 |  50 |   4 |   8 |  15 |  14  |      |    |
+  | 91   |  104 |  88 |  13 |  15 |  12 |  12  |      |    |
+  |      +------+-----+-----+-----+-----+------+------+----+
+  |Total.|  734 | 665 |  74 | 110 | 129 | 131  |   3  |  4 |
+  |      |      |     |     |     |     |      |      |    |
+  +------+------+-----+-----+-----+-----+------+------+----+
+
+  +------+------+------------------+
+  |      |      |                  |
+  |      |      |Cross-over values.|
+  |      |      |                  |
+  |      |      +------+-----+-----+
+  |Refer-|Total.|      |     |     |
+  |ence. |      |Verm- |     |Verm-|
+  |      |      |ilion |Sable|ilion|
+  |      |      |sable.| bar.|bar. |
+  +------+------+------+-----+-----+
+  |      |      |      |     |     |
+  ~147 I |  207 |   13 |  16 |  29 |
+  ~148 I |  256 |    9 |   9 |  18 |
+  |149 I |  239 |    8 |  15 |  22 |
+  |150 I |  236 |   10 |  19 |  27 |
+  |151 I |  289 |   10 |  18 |  26 |
+  | 89   |  239 |   13 |  11 |  23 |
+  | 90   |  140 |    9 |  21 |  29 |
+  | 91   |  244 |   11 |  10 |  21 |
+  |      +------+------+-----+-----+
+  |Total.|1,850 |   10 |  14 |  24 |
+  |      |      |      |     |     |
+  +------+------+------+-----+-----+
+
+TABLE 15.--_P_1 vermilion sable [female] [female] x bar [male] [male]. B.
+C. F_1 bar [female] x vermilion sable [male] [male]._
+
+  +------+----------+------------+-----------+------------+
+  |      | v s      |  v      B' | v  s   B' | v          |
+  |      | -------- | ---+------ | -----+--- | --+---+--- |
+  |      |       B' |      s     |           |     s   B' |
+  |      +------+---+-----+------+-----+-----+------+-----+
+  |Refer-|      |   |     |      |Verm-|     |      |     |
+  |ence. |Verm- |   |Verm-|      |ilion|Wild-|Verm- |Sable|
+  |      |ilion |Bar|ilion|Sable.|sable|type.|ilion.| bar.|
+  |      |sable.|   | bar.|      | bar.|     |      |     |
+  +------+------+---+-----+------+-----+-----+------+-----+
+  |105 I |   41 | 75|  10 |   4  |   5 |  11 |      |     ~
+  |106 I |   59 |122|  16 |  13  |  11 |  17 |      |     ~
+  |107 I |   92 | 98|   8 |  12  |  16 |  10 |      |     |
+  |116 I |  111 |149|  19 |  16  |  20 |  19 |      |   1 |
+  |117 I |   92 |117|  16 |  14  |  15 |  18 |      |     |
+  |126 I |   96 |160|  13 |  13  |  17 |  35 |      |     |
+  |127 I |  117 |124|  13 |  25  |  24 |  30 |   1  |     |
+  |      +------+---+-----+------+-----+-----+------+-----+
+  |Total |  608 |845|  95 |  97  | 108 | 140 |   1  |   1 |
+  +------+------+---+-----+------+-----+-----+------+-----+
+
+  +------+------+------------------+
+  |      |      |                  |
+  |      |      |Cross-over values.|
+  |      |      |                  |
+  |      |      +------+-----+-----+
+  |Refer-|Total.|      |     |     |
+  |ence. |      |Verm- |     |Verm-|
+  |      |      |ilion.|Sable|ilion|
+  |      |      |sable.| bar.|bar. |
+  +------+------+------+-----+-----+
+  ~105 I |  146 |   10 |  11 |  21 |
+  ~106 I |  238 |   12 |  12 |  24 |
+  |107 I |  236 |    9 |  11 |  20 |
+  |116 I |  335 |   11 |  12 |  22 |
+  |117 I |  272 |   11 |  12 |  23 |
+  |126 I |  334 |    8 |  15 |  23 |
+  |127 I |  334 |   12 |  16 |  28 |
+  |      +------+------+-----+-----+
+  |Total |1,895 |   10 |  13 |  23 |
+  +------+------+------+-----+-----+
+
+{42}
+
+In the third cross, vermilion (gray) bar entered from one side ([female])
+and (red) sable (not-bar) from the other ([male]). The daughters are bar
+and the sons vermilion bar. The daughters were back-crossed singly to
+vermilion sable males and gave the data in table 16.
+
+TABLE 16.--_P_1 vermilion bar_ [female] [female] x _sable_ [male] [male].
+_B. C. F_1 bar_ [female] x _vermilion sable_ [male] [male].
+
+  +-----------+--------------+------------+-------------+---------------+
+  |           |    v   B'    |  v  s      |   v         |   v  s  B'    |
+  |           |    -----     |  -+------  |   -----+--  |   -+---+--    |
+  |Reference. |      s       |        B'  |       s B'  |               |
+  |           +-------+------+------+-----+-------+-----+---------+-----+
+  |           |  Ver- |Sable.| Ver- | Bar.| Ver-  |Sable|Vermilion|Wild-|
+  |           | milion|      |milion|     |milion.|bar. |  sable  |type.|
+  |           | bar.  |      |sable.|     |       |     |   bar.  |     |
+  +-----------+-------+------+------+-----+-------+-----+---------+-----+
+  | 129 I     |  132  |  147 |  15  | 15  |  19   |  21 |     1   |  1  ~
+  | 130 I     |  194  |  168 |  21  | 17  |  28   |  25 |    ..   |  1  ~
+  | 131 I     |  121  |   89 |  10  | 20  |  26   |  11 |     1   |  1  |
+  | 137 I     |  139  |  113 |  19  | 12  |  33   |  14 |    ..   |  1  |
+  | 138 I     |  131  |  128 |  11  | 11  |  28   |  24 |     1   |  .. |
+  | 139 I     |   83  |   79 |   4  | 12  |  17   |  12 |    ..   |  .. |
+  |           +-------+------+------+-----+-------+-----+---------+-----+
+  |   Total.  |  800  |  724 |  80  | 87  | 151   | 107 |     3   |  4  |
+  +-----------+-------+------+------+-----+-------+-----+---------+-----+
+
+  +-----------+-------+-------------------------+
+  |           |       |                         |
+  |           |       |                         |
+  |Reference. | Total.|  Cross-over values.     |
+  |           |       +---------+-----+---------+
+  |           |       |Vermilion|Sable|Vermilion|
+  |           |       |sable.   |bar. |bar.     |
+  +-----------+-------+---------+-----+---------+
+  ~ 129 I     |   351 |    9    |  12 |   20    |
+  ~ 130 I     |   454 |    9    |  12 |   20    |
+  | 131 I     |   279 |   12    |  14 |   24    |
+  | 137 I     |   331 |   10    |  15 |   24    |
+  | 138 I     |   334 |    7    |  16 |   22    |
+  | 139 I     |   207 |    8    |  14 |   22    |
+  |           +-------+---------+-----+---------+
+  |   Total.  | 1,956 |    9    |  14 |   22    |
+  +-----------+-------+---------+-----+---------+
+
+In the fourth cross, vermilion sable bar entered from one side, and (red
+gray not-bar) wild type from the other. The daughters were bar and the sons
+vermilion sable bar. The daughters were back-crossed singly to vermilion
+sable males, with the results shown in table 17.
+
+TABLE 17.--_P_1 vermilion sable bar_ [female] [female] x _wild_ [male]
+[male]. _B. C. F_1 bar_ [female] x _vermilion sable_ [male] [male].
+
+  +-----------+---------------+--------------+------------+--------------+
+  |           |    v  s  B'   |    v         |  v  s      |    v   B'    |
+  |           |    --------   |    -+-----   |  -----+--  |    -+-+--    |
+  | Reference.|               |      s  B'   |        B'  |      s       |
+  |           +---------+-----+--------+-----+-------+----+-------+------+
+  |           |Vermilion|Wild-|  Ver-  |Sable|  Ver- |Bar.|  Ver- |Sable.|
+  |           |  sable  |type | milion.|bar. | milion|    | milion|      |
+  |           |  bar.   |     |        |     | sable.|    |  bar. |      |
+  +-----------+---------+-----+--------+-----+-------+----+-------+------+
+  | 132 I     |    95   | 108 |   10   |  13 |   24  | 22 |  ..   |  ..  ~
+  | 133 I     |   112   | 150 |   18   |  16 |   26  | 16 |  1    |  2   ~
+  | 134 I     |    84   |  95 |   14   |   7 |   15  | 16 |  ..   |  1   |
+  | 135 I     |   100   |  86 |   16   |  17 |   19  | 22 |  ..   |  1   |
+  | 152 I     |    73   |  88 |   12   |   8 |   14  | 18 |  ..   |  ..  |
+  | 153 I     |   114   | 138 |   12   |  12 |   17  | 17 |  ..   |  ..  |
+  | 154 I     |    63   |  90 |   10   |   8 |    8  | 15 |  ..   |  ..  |
+  |           |         |     |        |     |       |    |       |      |
+  |   Total.  |   641   | 755 |   92   |  81 |  123  |126 |  1    |  4   |
+  +-----------+---------+-----+--------+-----+-------+----+-------+------+
+
+  +-----------+------+-------------------------+
+  |           |      |                         |
+  |           |      |                         |
+  | Reference.|Total.|  Cross-over values.     |
+  |           |      +---------+-----+---------+
+  |           |      |Vermilion|Sable|Vermilion|
+  |           |      |sable.   |bar. |bar.     |
+  +-----------+------+---------+-----+---------+
+  ~ 132 I     |  272 |    9    |  17 |    25   |
+  ~ 133 I     |  341 |   11    |  13 |    22   |
+  | 134 I     |  232 |   10    |  14 |    22   |
+  | 135 I     |  261 |   13    |  16 |    28   |
+  | 152 I     |  213 |    9    |  15 |    24   |
+  | 153 I     |  310 |    8    |  11 |    19   |
+  | 154 I     |  194 |    9    |  12 |    21   |
+  |           |      |         |     |         |
+  |   Total.  |1,823 |   10    |  14 |    23   |
+  +-----------+------+---------+-----+---------+
+
+{43}
+
+In tables 14 to 17 the calculations for the three cross-over values for
+vermilion, sable, and bar are given for the separate cultures and for the
+totals. The latter are here repeated.
+
+  +-----------+-----------+---------+-----------+
+  | From--    | Vermilion |  Sable  | Vermilion |
+  |           |  sable.   |   bar.  |    bar.   |
+  +-----------+-----------+---------+-----------+
+  | Table 14  |    10     |    14   |     24    |
+  |       15  |    10     |    13   |     23    |
+  |       16  |     9     |    14   |     22    |
+  |       17  |    10     |    14   |     23    |
+  +-----------+-----------+---------+-----------+
+
+The results of the different experiments are remarkably uniform. There can
+be no doubt that the cross-over value is independent of the way in which
+the experiment is made, whether any two recessives enter from the same or
+from opposite sides.
+
+TABLE 18.--_Linkage of vermilion, sable, and bar with balanced viability._
+
+  +---------------------+---------+---------+---------+---------+-------+
+  |                     | ------- | --+---- | ----+-- | --+-+-- | Total.|
+  +---------------------+---------+---------+---------+---------+-------+
+  | Wild-type           |   755   |   110   |   140   |    4    |       |
+  | Vermilion           |   734   |    92   |   151   |    1    |       |
+  | Sable               |   724   |    97   |   131   |    4    |       |
+  | Bar                 |   845   |    87   |   126   |    4    |       |
+  | Vermilion sable     |   608   |    80   |   123   |    3    |       |
+  | Vermilion bar       |   800   |    95   |   129   |    1    |       |
+  | Sable bar           |   665   |    81   |   107   |    1    |       |
+  | Vermilion sable bar |   641   |    74   |   108   |    3    |       |
+  |                     +---------+---------+---------+---------+-------+
+  |     Total           | 5,772   |   716   | 1,015   |   21    | 7,524 |
+  |     Percentage      |  76.7   |  9.53   | 13.49   | 0.28    |       |
+  +---------------------+---------+---------+---------+---------+-------+
+
+In table 18 the data from each of the four separate experiments have been
+combined in the manner explained, so that viability is canceled to the
+greatest extent. The amount of each kind of cross-over appears at the
+bottom of the table. The total amount of crossing-over between vermilion
+and sable is the sum of the single (9.53) and of the double (0.28)
+cross-overs, which value is 9.8. Likewise the cross-over value for sable
+bar is 13.49 + 0.28 (= 14), and for vermilion bar is 9.53 + 13.49 (= 23).
+By means of these cross-over values we may calculate the coincidence
+involved, which is in this case
+
+            0.0028 x 100
+  --------------------------------- = 20.8
+  0.0953 + 0.0028 x 0.1349 + 0.0028
+
+This value shows that there actually occurs only about 21 per cent of the
+double cross-overs which from the values of the single cross-overs are
+expected to occur in this section of the chromosome. This is the result
+which is to be anticipated upon the chromosome view, for if crossing-over
+is connected with loops of the chromosomes, and if these loops have an
+average length, then if the chromosomes cross over at one {44} point it is
+unlikely they will cross over again at another point nearer than the
+average length of the loop.
+
+The calculation of the locus for sable gives 43.0.
+
+DOT.
+
+In the F_2, from a cross of a double recessive (white vermilion) female by
+a triple recessive (eosin vermilion pink) male, there appeared, July 21,
+1912, three white-eyed females which had two small, symmetrically placed,
+black, granular masses upon the thorax. These "dots" appeared to be dried
+exudations from pores. It did not seem possible that such an effect could
+be inherited, but as this condition had never been observed before, it
+seemed worth while to mate the three females to their brothers. In the next
+generation about 1 per cent of the males were dotted. From these females
+and males a stock was made up which in subsequent generations showed from
+10 to 50 per cent of dot. Selection seemed to have no effect upon the
+percentage of dot. Although the stock never showed more than 50 per cent of
+dot, yet it was found that the normal individuals from the stock threw
+about the same per cent as did those that were dotted, so that the stock
+was probably genetically pure. The number of males which showed the
+character was always much smaller than the number of dotted females; in the
+hatches which produced nearly 50 per cent of dot, nearly all the females
+but very few of the males were dotted. Quite often the character showed on
+only one side of the thorax.
+
+Since this character arose in an experiment involving several eye-colors an
+effort was made by crossing to wild and extracting to transfer the dot to
+flies normal in all other respects. This effort succeeded only partly, for
+a stock was obtained which differed from the wild type only in that it bore
+dot (about 30 per cent) and in that the eyes were vermilion. Several
+attempts to get the dot separated from vermilion failed. Since this was
+only part of the preliminary routine work necessary to get a mutant stock
+in shape for exact experimentation, no extensive records were kept.
+
+LINKAGE OF VERMILION AND DOT.
+
+When a dot male with vermilion eyes was bred to a wild female the offspring
+were wild-type males and females. These inbred gave the data shown in table
+19.
+
+TABLE 19.--_P_1 vermilion dot [male] x wild [female] [female]. F_1
+wild-type [female] [female] x F_1 wild-type [male] [male]._
+
+  +------------+----------+-----------+-----------+-------------+---------+
+  | Reference. | F_2      | Wild-type | Vermilion | Vermilion   | Dot     |
+  |            | females. | [male].   | [male].   | dot [male]. | [male]. |
+  +------------+----------+-----------+-----------+-------------+---------+
+  |  7         |   345    |    151    |    130    |      0      |    0    |
+  |  8         |   524    |    245    |    220    |      3      |    0    |
+  |            +----------+-----------+-----------+-------------+---------+
+  |     Total. |   869    |    396    |    350    |      3      |    0    |
+  +------------+----------+-----------+-----------+-------------+---------+
+
+{45}
+
+Only three dot individuals appeared in F_2, but since these were males the
+result indicates that the dot character is due to a sex-linked gen. These
+three males had also vermilion eyes, indicating linkage of dot and
+vermilion. The males show no deficiency in numbers, therefore the
+non-appearance of the dot can not be due to its being semi-lethal. It
+appears, therefore, that the expression of the character must depend on the
+presence of an intensifying factor in one of the autosomes, or more
+probably, like club, it appears only in a small percentage of flies that
+are genetically pure for the character.
+
+The reciprocal cross (dot female with vermilion eyes by wild male) was made
+(table 20). The daughters were wild type and the sons vermilion. Not one of
+the 272 sons showed dot. If the gen is sex-linked the non-appearance of dot
+in the F_1 males can be explained on the ground that males that are
+genetically dot show dot very rarely, or that its appearance is dependent
+upon the intensification by an autosomal factor of the effect produced by
+the sex-linked factor for dot.
+
+TABLE 20.--_P_1 vermilion dot [female] x wild [male]._
+
+  A = Wild-type [female].
+  B = Vermilion [male].
+  C = Wild-type [male].
+  D = Wild-type [female].
+  E = Vermilion [male].
+  F = Vermilion [female].
+  G = Vermilion dot [male].
+  H = Vermilion dot [female].
+  I = Dot [male].
+  J = Dot [female].
+
+  +--------------------++-----------------------------------------------+
+  |  First generation. ||              Second generation.               |
+  +----------+----+----++----------+----+----+----+----+----+---+---+---+
+  |Reference.| A  | B  ||Reference.| C  | D  | E  | F  | G  | H | I | J |
+  +--------------------++----------+----+----+----+----+----+---+---+---+
+  |  137 C.  | 44 | 45 ||   19     |211 |198 |228 |206 | 20 | 3 | 0 | 0 |
+  |  138 C.  | 77 | 62 ||   22     |266 |220 |227 |227 | 16 | 0 | 0 | 0 |
+  |          |124 |124 ||   28     |143 |149 |125 |124 | 14 | 1 | 0 | 0 |
+  |          | 57 | 41 ||          +----+----+----+----+----+---+---+---+
+  |          |----|----||    Total.|620 |567 |570 |557 | 50 | 4 | 0 | 0 |
+  |    Total.|291 |272 ||          |    |    |    |    |    |   |   |   |
+  +--------------------++----------+----+----+----+----+----+---+---+---+
+
+The F_2 generation is given in table 20. The dot reappeared in F_2 both in
+females and in males, but instead of appearing in 50 per cent of both
+sexes, as expected if it is simply sex-linked, it appeared in 4.0 per cent
+in the females and in only 0.4 per cent in the males. The failure of the
+character to be fully realized is again apparent, but here, where it is
+possible for it to be realized equally in males and females, we find that
+there are 50 females with dot to only 4 dot males. This would indicate that
+the character is partially "_sex-limited_" (Morgan, 1914_d_) in its
+realization. The dot appeared only in flies with vermilion eyes, indicating
+extremely strong linkage between vermilion and dot.
+
+The evidence from the history of the stock, together with these
+experiments, shows that the character resembles club (wing) in that it is
+not expressed somatically in all the flies which are homozygous for it. In
+the case of club we were fortunate enough to find a constant feature {46}
+which we could use as an index, but, so far as we have been able to see,
+there is no such constant accessory character in the case of the dot.
+Unlike club, dot is markedly sex-limited in its effect; that is, there is a
+difference of expression of the gen in the male and female. This difference
+recalls the sexual dimorphism of the eosin eye.
+
+BOW.
+
+In an F_2 generation from rudimentary males by wild females there appeared,
+August 15, 1912, a single male whose wings instead of being flat were
+turned down over the abdomen (fig. c). The curvature was uniform throughout
+the length of the wing. A previous mutation, arc, of this same type had
+been found to be a recessive character in the second group. The new
+mutation, bow, is less extreme than arc and is more variable in the amount
+of curvature. When the bow male was mated to wild females the offspring had
+straight wings.
+
+[Illustration: FIG. C.--Bow wing.]
+
+TABLE 21.--_P_1 bow [male][male] x wild [female][female]._
+
+  +------------------------------------------+
+  |           First generation.              |
+  +----------+-----------------+-------------+
+  |Reference.|    Wild-type    |  Wild-type  ~
+  |          |[female][female].|[male][male].~
+  +----------+-----------------+-------------+
+  |  169 C.  |       17        |     17      |
+  +----------+-----------------+-------------+
+
+  +--------------------------------------------------------+
+  |              Second generation.                        |
+  +----------+-----------------+-------------+-------------+
+  ~Reference.|   Wild-type     |  Wild-type  |    Bow      |
+  ~          |[female][female].|[male][male].|[male][male].|
+  +----------+-----------------+-------------+-------------+
+  |   18 I.  |       193       |     145     |     67      |
+  |   21 I   |       182       |     100     |     49      |
+  |          +-----------------+-------------+-------------+
+  |    Total.|       375       |     245     |    116      |
+  +----------+-----------------+-------------+-------------+
+
+{47}
+
+The F_2 ratio in table 21 is evidently the 2:1:1 ratio typical of
+sex-linkage, but with the bow males running behind expectation. This
+deficiency is due in part to viability but more to a failure to recognize
+all the bow-winged individuals, so that some of them were classified among
+the not-bow or straight wings. In favor of the view that the classification
+was not strict is the fact that the sum of the two male classes about
+equals the number of the females.
+
+BOW BY ARC.
+
+When this mutant first appeared its similarity to arc led us to suspect
+that it might be arc itself or an allelomorph of arc. It was bred,
+therefore, to arc. The bow male by arc females gave straight (normal)
+winged males and females. The appearance of straight wings shows that bow
+is not arc nor allelomorphic to arc. When made later, the reciprocal cross
+of bow female by arc male gave in F_1 straight-winged females but bow
+males. This result is in accordance with the interpretation that bow is a
+sex-linked recessive. Further details of these last two experiments may now
+be given. The F_1 (wild-type) flies from bow male by arc female were
+inbred. The data are given in table 22.
+
+TABLE 22.--_P_1 bow [male] x arc [female]._
+
+  +--------------------------------------------+
+  |            First generation.               |
+  +----------+------------------+--------------+
+  |Reference.|    Wild-type     |  Wild-type   ~
+  |          |[female] [female].|[male] [male].~
+  +----------+------------------+--------------+
+  |   71 C.  |       48         |      43      |
+  |   75 C.  |       28         |      27      |
+  |          +------------------+--------------+
+  |    Total.|       76         |      70      |
+  +----------+------------------+--------------+
+
+  +------------------------------+
+  |      Second generation.      |
+  +----------+---------+---------+
+  ~Reference.|Straight.|  Not-   |
+  ~          |         |straight.|
+  +----------+---------+---------+
+  |   71 C.  |   179   |   133   |
+  +----------+---------+---------+
+
+Bow and arc are so much alike that they give a single rather variable
+phenotypic class in F_2. Therefore the F_2 generation is made up of only
+two separable classes--flies with straight wings and flies with
+not-straight wings. The ratio of the two should be theoretically 9:7, which
+is approximately realized in 179:133.
+
+If the distribution of the characters according to sex is ignored, the case
+is similar to the case of the two white races of sweet peas, which bred
+together gave wild-type or purple peas in F_1 and in F_2 gave 9 colored to
+7 white. If sex is taken into account, the theoretical expectation for the
+F_2 females is 6 straight to 2 arc, and for the F_2 males 3 straight to 1
+arc to 3 bow to 1 bow-arc.
+
+The F_1 from bow females by arc male and their F_2 offspring are given in
+table 23. {48}
+
+TABLE 23.--_P_1 bow [female] x arc [male]._
+
+  +--------------------------------------------+
+  |           First generation.                |
+  |----------+------------------+--------------+
+  |Reference.|    Wild-type     |     Bow      |
+  |          |[female] [female].|[male] [male].|
+  |----------+------------------+--------------+
+  |  72 C.   |       22         |      19      ~
+  |  73 C.   |       12         |      10      ~
+  |   5 I.   |       22         |      21      |
+  |  74 C.   |       56         |      52      |
+  |          |------------------+--------------+
+  |    Total.|      112         |     102      |
+  +----------+------------------+--------------+
+
+  +------------------------------+
+  |         Second generation.   |
+  +----------+---------+---------+
+  |Reference.|Straight.|  Not-   |
+  |          |         |straight.|
+  +----------+---------+---------+
+  ~    3 I.  |   56    |   69    |
+  ~  3.1 I.  |   46    |   62    |
+  |    5 I.  |   56    |   68    |
+  |  5.1 I.  |   90    |  108    |
+  +----------+---------+---------+
+  |    Total.|  248    |  307    |
+  +----------+---------+---------+
+
+In this case the F_2 expectation is 6 straight to 10 not-straight. Since
+the sex-linked gen bow entered from the female, half the F_2 males and
+females are bow. The half that are not-bow consist of 3 straight to 1 arc,
+so that both in the female classes and in the male classes there are 3
+straight to 5 not-straight or in all 6 straight to 10 not-straight. The
+realized result, 248 straight to 307 not-straight, is more nearly a 3:4
+ratio, due probably to a wrong classification of some of the bow as
+straight.
+
+LEMON BODY-COLOR.
+
+(Plate I, figure 3.)
+
+A few males of a new mutant with a lemon-colored body and wings appeared in
+August 1912. The lemon flies (Plate II, fig. 3) resemble quite closely the
+yellow flies (Plate II, fig. 4). They are paler and the bristles, instead
+of being brown, are black. These flies are so weak that despite most
+careful attention they get stuck to the food, so that they die before
+mating. The stock was at first maintained in mass from those cultures that
+gave the greatest percentage of lemon flies. In a few cases lemon males
+mated with their gray sisters left offspring, but the stock obtained in
+this way had still to be maintained by breeding heterozygotes, as stated
+above. But from the gray sisters heterozygous for lemon (bred to lemon
+males) some lemon females were also produced.
+
+LINKAGE OF CHERRY, LEMON, AND VERMILION.
+
+In order to study the linkage of lemon, the following experiment was
+carried out. Since it was impracticable to breed directly from the lemon
+flies, virgin females were taken from stock throwing lemon, and were mated
+singly to cherry vermilion males. Only a few of the females showed
+themselves heterozygous for lemon by producing lemon as well as gray sons.
+Half the daughters of such a pair are expected to be heterozygous for lemon
+and also for cherry and vermilion, which went in from the father. These
+daughters were mated singly to cherry vermilion males, and those that gave
+some lemon sons were continued, {49} and are recorded in table 24. The four
+classes of females were not separated from each other, but the total of
+females is given in the table.
+
+TABLE 24.--_P_1 lemon (het.) [female] x cherry vermilion [male] [male]. F_1
+wild-type [female] x cherry vermilion [male] [male]._
+
+  +-------+--------------+-------------+-------------+-------------+------+
+  |       |  W^c     V   |  W^c l_m    |  W^c        |  W^c l_m V  |      |
+  |       |  ----------  |  ---+------ | ------+---  | ---+----+---|      |
+  |       |     l_m      |           V |    l_m  V   |             |      |
+  |Females+-------+------+------+------+------+------+-------+-----+ Total|
+  |       |Cherry |      |Cherry| Ver- |Cherry|Lemon |Cherry |Wild |[male]|
+  |       | ver-  |Lemon.|lemon.|milion|      | ver- |lemon  |type.|[male]|
+  |       |milion.|      |      |      |      |milion| ver-  |     |      |
+  |       |       |      |      |      |      |      |milion.|     |      |
+  +-------+-------+------+------+------+------+------+-------+-----+------+
+  |   71  |   42  |  19  |  2   |   6  |  3   |  6   |  0    |  0  |  78  |
+  |   88  |   26  |  19  |  2   |   8  |  8   |  4   |  0    |  0  |  67  |
+  |   36  |   28  |   7  |  0   |   2  |  1   |  0   |  0    |  0  |  38  |
+  |   51  |   12  |  22  |  0   |   4  |  4   |  4   |  0    |  0  |  46  |
+  |   98  |   29  |  35  |  0   |   8  |  5   |  1   |  0    |  0  |  78  |
+  |   47  |   17  |  11  |  0   |   1  |  3   |  2   |  0    |  0  |  34  |
+  |   46  |   23  |  20  |  1   |   6  |  5   |  2   |  0    |  0  |  57  |
+  +-------+-------+------+------+------+------+------+-------+-----+------+
+  |  437  |  177  | 133  |  5   |  35  | 29   | 19   |  0    |  0  | 398  |
+  +-------+-------+------+------+------+------+------+-------+-----+------+
+
+There are three loci involved in this cross, namely, cherry, lemon, and
+vermilion. Of these loci two were known, cherry and vermilion. The data are
+consistent with the assumption that the lemon locus is between cherry and
+vermilion, for the double cross-over classes (the smallest classes) are
+cherry lemon vermilion and wild type. The number of single cross-overs
+between cherry and lemon and between lemon and vermilion are also
+consistent with this assumption. Since lemon flies fail to emerge
+successfully, depending in part upon the condition of the bottle, the
+classes involving lemon are worthless in calculating crossing-over and are
+here ignored. In other words, lemon may be treated as though it did not
+appear at all, _i. e._, as a lethal. The not-lemon classes--cherry,
+vermilion, cherry vermilion, and wild type--give the following approximate
+cross-over values for the three loci involved: Cherry lemon, 15; lemon
+vermilion, 12; cherry vermilion, 27. The locus of lemon, calculated by
+interpolation, is at about 17.5.
+
+LETHAL 2.
+
+In September 1912 a certain wild female produced 78 daughters and only 16
+sons (Morgan, 1914_b_); 63 of these daughters were tested and 31 of them
+gave 2 females to 1 male, while 32 of them gave 1:1 sex-ratios. This shows
+that the mother of the original high sex-ratio was heterozygous for a
+recessive sex-linked lethal. In order to determine the position of this
+lethal, a lethal-bearing female was bred to an eosin (or white) miniature
+male, and those daughters that were heterozygous for eosin, lethal, and
+miniature were then back-crossed to {50} eosin miniature males. The
+daughters that result from such a cross give only the amount of
+crossing-over between eosin and miniature (as 29.7), but the males give the
+cross-over values for eosin lethal (9.9), lethal miniature (15.4), and
+eosin miniature (25.1). The data for this cross are given in table 25.
+
+TABLE 25.--_Total data upon linkage of eosin, lethal 2, and miniature, from
+Morgan, 1914b._
+
+  +------------------------------------+
+  |             Females.               |
+  +--------+--------------+------------+
+  |        |              |            |
+  | Total. | Cross-overs. | Cross-over |
+  |        |              | value.     ~
+  |        |              |            ~
+  +--------+--------------+------------+
+  | 15,904 |    4,736     |    29.7    |
+  +--------+--------------+------------+
+
+  +-----------------------------------------------------------------------+
+  |                                 Males.                                |
+  +--------+--------+--------+---------+----------------------------------+
+  |w^e    m|w^e l_2 |w^e     |w^e l_2 m|        Cross-over values.        |
+  |--------|---+----|------+-|---+---+-+----------+-----------+-----------+
+  ~    l_2 |       m|   l_2 m|         | Eosin    | Lethal 2  | Eosin     |
+  ~        |        |        |         | lethal 2.| miniature.| miniature.|
+  +--------+--------+--------+---------+----------+-----------+-----------+
+  |  5,045 |   653  |  1,040 |    14   |    9.9   |    15.4   |    25.1   |
+  +--------+--------+--------+---------+----------+-----------+-----------+
+
+A similar experiment, in which eosin and vermilion were used instead of
+eosin and miniature, is summarized in table 26.
+
+TABLE 26.--_Total data upon the linkage of eosin, lethal 2, and vermilion,
+from Morgan, 1914b._
+
+  +------------------------------------+
+  |            Females.                |
+  +--------+--------------+------------+
+  |        |              |            |
+  | Total. | Cross-overs. | Cross-over |
+  |        |              | value.     ~
+  |        |              |            ~
+  +--------+--------------+------------+
+  |  2,656 |      729     |    27.5    |
+  +--------+--------------+------------+
+
+  +-----------------------------------------------------------------------+
+  |                                Males.                                 |
+  +--------+--------+--------+---------+----------------------------------+
+  |w^e    v|w^e l_2 |w^e     |w^e l_2 v|        Cross-over values.        |
+  |--------|---+----|------+-|---+---+-+----------+-----------+-----------+
+  ~    l_2 |       v|   l_2 v|         | Eosin    | Lethal 2  | Eosin     |
+  ~        |        |        |         | lethal 2.| vermilion.| vermilion.|
+  +--------+--------+--------+---------+----------+-----------+-----------+
+  |   902  |   124  |   227  |    6    |    10.3  |    18.5   |    27.9   |
+  +--------+--------+--------+---------+----------+-----------+-----------+
+
+Considerable data in which lethal was not involved were also obtained in
+the course of these experiments and are included in the summary of the
+total data given in table 27.
+
+TABLE 27.--_Summary of all data upon lethal 2, from Morgan, 1914b._
+
+  +--------------------+--------+--------------+------------+
+  | Gens.              | Total. | Cross-overs. | Cross-over |
+  |                    |        |              | values.    |
+  +--------------------+--------+--------------+------------+
+  | White lethal 2     |  8,011 |      767     |     9.6    |
+  | White vermilion    |  6,023 |    1,612     |    26.8    |
+  | White miniature    | 36,021 |   11,048     |    30.7    |
+  | Lethal 2 vermilion |  1,400 |      248     |    17.7    |
+  | Lethal 2 miniature |  6,752 |    1,054     |    15.4    |
+  +--------------------+--------+--------------+------------+
+
+The amount of crossing-over between eosin and lethal is about 10 per cent
+and the amount of crossing-over between lethal and miniature is about 18
+per cent. Since the amount of crossing-over between eosin {51} and
+miniature is over 30 per cent, the lethal factor must lie between eosin and
+miniature, somewhat nearer to eosin. It is impossible at present to locate
+lethal 2 accurately because of a real discrepancy in the data, which makes
+it appear that lethal 2 extends for a distance of about 5 units along the
+chromosome from about 10 to about 15. Work is being done which it is hoped
+will make clear the reason for this. For the present we may locate lethal 2
+at the midpoint of its range, or at 12.5.
+
+CHERRY.
+
+(Plate II, figure 9.)
+
+The origin of the eye-color cherry has been given by Safir (Biol. Bull.,
+1913).
+
+Cherry appeared (October 1912) in an experiment involving vermilion
+eye-color and miniature wings. This is the only time the mutant has ever
+come up, and although several of this mutant (males) appeared in Safir's
+experiment, they may have all come from the same mother. It is probable
+that the mutation occurred in the vermilion stock only a generation or so
+before the experiment was made, for otherwise cherry would be expected to
+be found also in the vermilion stock from which the mothers were taken;
+however, it was not found.
+
+A SYSTEM OF QUADRUPLE ALLELOMORPHS.
+
+Safir has described crosses between this eye-color and red, white, eosin,
+and vermilion. We conclude for reasons similar to those given by Morgan and
+Bridges (Jour. Exp. Zool., 1913) for the case of white and eosin, that
+cherry is an allelomorph of white and of eosin. This is not the
+interpretation followed in Safir's paper, where cherry is treated as though
+absolutely linked to white or to eosin. Both interpretations give, however,
+the same numerical result for each cross considered by itself. Safir's data
+and those which appear in this paper show that white, eosin, cherry, and a
+normal (red) allelomorph form a system of quadruple allelomorphs. If this
+interpretation is correct, then the linkage relations of cherry should be
+identical with those of white or of eosin.
+
+LINKAGE OF CHERRY AND VERMILION.
+
+The cross-over value for white (eosin) and vermilion, based on a very large
+amount of data, is about 31 units. An experiment of our own in which cherry
+was used with vermilion gave a cross-over value of 31 units, which is a
+close approximation to the cross-over value of white and vermilion. The
+cross which gave this data was that of a cherry vermilion (double
+recessive) male by wild females. The F_{1} wild-type flies inbred gave a
+single class of females (wild-type) and the males in four classes which
+show by the deviation from a 1:1:1:1 ratio the amount of crossing-over
+involved. {52}
+
+In one of the F_{2} male classes of table 28 the simple eye-color cherry
+appeared for the first time (since the original mutant was vermilion as
+well as cherry). Safir has recorded a similar cross with like results.
+
+TABLE 28.--_P_{1} cherry vermilion [male] [male] x wild [female] [female].
+F_{1} wild-type [female] [female] x F_{1} wild-type [male] [male]._
+
+  +----------+---------+----------------+---------------+-------+------+
+  |          |         | Non-cross-over |  Cross-over   |       |      |
+  |          |         |     [male].    |    [male].    |       |      |
+  |          |Wild-type+----------+-----+-------+-------+Total  |Cross-|
+  |Reference.|[female] | Cherry   |Wild-|Cherry.| Ver-  |[male] |over  |
+  |          |[female].|vermilion.|type.|       |milion.|[male].|value.|
+  +----------+---------+----------+-----+-------+-------+-------+------+
+  |  160 C   |  188    |   57     |  61 |   32  |  34   |  184  |  36  |
+  |  161 C   |  256    |   85     |  93 |   40  |  52   |  270  |  34  |
+  |  162 C   |  251    |   78     |  78 |   20  |  37   |  213  |  26  |
+  |  163 C   |  229    |   76     |  95 |   34  |  33   |  238  |  28  |
+  +----------+---------+----------+-----+-------+-------+-------+------+
+  |  Total   |  924    |  296     | 327 |  126  | 156   |  905  |  31  |
+  +----------+---------+----------+-----+-------+-------+-------+------+
+
+Some cherry males were bred to wild females. The F_{1} wild-type males and
+females inbred gave the results shown in table 29. Some of the cherry males
+thus produced were bred to their sisters. Cherry females as well as males
+resulted; and it was seen that the eye-color is the same in the males and
+females, in contradistinction to the allelomorph eosin, where there is a
+marked bicolorism (figs. 7, 8, Plate II). The cherry eye-color is almost
+identical with that of the eosin female, but is perhaps slightly more
+translucent and brighter.
+
+TABLE 29.--_P_{1} cherry [male] [male] x wild [female] [female]. F_{1}
+wild-type [female] [female] x F_{1} wild-type [male] [male]._
+
+  +------------+---------------------+-------------------+----------------+
+  | Reference. | Wild-type [female]. | Wild-type [male]. | Cherry [male]. |
+  +------------+---------------------+-------------------+----------------+
+  |  15 I      |        266          |       120         |     100        |
+  +------------+---------------------+-------------------+----------------+
+
+  +------------+-------------------------------------+
+  |            |        First generation.            |
+  | Reference. +--------------------+----------------+
+  |            | White-cherry       |                |
+  |            | compound [female]. | Cherry [male]. |
+  +------------+--------------------+----------------+
+  | 9 M        |        321         |       302      |
+  +------------+--------------------+----------------+
+
+Eosin-cherry compound was also made. An eosin female was mated to a cherry
+male. The eosin-cherry daughters were darker than their eosin brothers.
+Inbred they gave the results shown in table 31.
+
+TABLE 31.--_P_1 eosin [female] x cherry [male]._
+
+  +------------------------------------------+
+  |              First generation.           |
+  +------------+-------------------+---------+
+  |            | Eosin-cherry      | Eosin   |
+  | Reference. | compound          | [male]  |
+  |            | [female][female]. | [male]. ~
+  |            |                   |         ~
+  +------------+-------------------+---------+
+  |  43C       |         71        |    58   |
+  +------------+-------------------+---------+
+
+  +----------------------------------------------------+
+  |               Second generation.                   |
+  +------------+-------------------+---------+---------+
+  |            | Eosin and         |         |         |
+  | Reference. | eosin-cherry      | Cherry  | Eosin   |
+  ~            | compound          | [male]. | [male]. |
+  ~            | [female][female]. |         |         |
+  +------------+-------------------+---------+---------+
+  |  1I        |        154        |    99   |    62   |
+  |  2I        |        174        |    74   |    77   |
+  |            +-------------------+---------+---------+
+  |            |        328        |   173   |   139   |
+  +------------+-------------------+---------+---------+
+
+Although in the F_2 results there are two genotypic classes of females,
+namely, pure eosin and eosin-cherry compound, the eye-colors are so nearly
+the same that they can not be separated. The two classes of males can be
+readily distinguished; of these, one class, cherry, has the same color as
+the females, while the other class, eosin, is much lighter. Such an F_2
+group will perpetuate itself, giving one type of female (of three possible
+genotypic compositions, but somatically practically homogeneous) and two
+types of males, only one of which is like the females.
+
+FUSED.
+
+In a cross between purple-eyed[6] males and black females there appeared in
+F_2 (Nov. 4, 1912) a male having the veins of the wing arranged as shown in
+text-figure D b. It will be seen that the third and the fourth longitudinal
+veins are fused from the base to and beyond the {53} point at which in
+normal flies the anterior cross-vein lies. The cross-vein and the cell
+normally cut off by it are absent. There are a number of other features
+(see fig. D _c_) characteristic of this mutation: the wings are held out at
+a wide angle from the body, the ocelli are very much reduced in size or
+entirely absent, the bristles around the ocelli are usually small. The
+females are absolutely sterile, not only with their own, but with any
+males.
+
+Fused males by wild females gave wild-type males and females. Inbred these
+gave the results shown in table 32. The fused character reappeared only in
+the F_2 males, showing that it is a recessive sex-linked character.
+
+TABLE 32.--_P_1 fused [male] x wild [female][female]._
+
+  +-------------------------------------------------+
+  |              First generation.                  |
+  +------------+-------------------+----------------+
+  | Reference. | Wild-type         | Wild-type      ~
+  |            | [female][female]. | [male][male].  ~
+  +------------+-------------------+----------------+
+  |  4I        |         66        |       43       |
+  |            |                   |                |
+  +------------+-------------------+----------------+
+
+  +------------------------------------------------------------------+
+  |               Second generation.                                 |
+  +------------+-------------------+----------------+----------------+
+  ~ Reference. | Wild-type         | Wild-type      | Fused          |
+  ~            | [female][female]. | [male][male].  | [male][male].  |
+  +------------+-------------------+----------------+----------------+
+  |  190C      |        258        |       96       |       115      |
+  |   14I      |        239        |      105       |        90      |
+  |            +-------------------+----------------+----------------+
+  |  Total     |        497        |      201       |       205      |
+  +------------+-------------------+----------------+----------------+
+
+The reciprocal cross was tried many times, but is impossible, owing to the
+sterility of the females. Since the fused females are sterile to fused
+males, the stock is kept up by breeding heterozygous females to fused
+males.
+
+By means of the following experiments the position of fused in the X
+chromosome was determined. A preliminary test was made by mating with
+eosin, whose factor lies near the left end of the X chromosome series.
+
+LINKAGE OF EOSIN AND FUSED.
+
+Fused (red-eyed) males mated to eosin (not-fused) females gave wild-type
+daughters and eosin sons, which inbred gave the classes shown in table 33.
+
+TABLE 33.--_P_1 eosin [female][female] x fused [male][male]. F_1 wild-type
+[female][female] x F_1 eosin [male][male]._
+
+  +----------+--------+-----------------+----------------+-------+--------+
+  |          |        | Non-cross-over  | Cross-over     |       |        |
+  |          |        | [male][male].   | [male][male].  | Total | Cross- |
+  |Reference.|Females.+--------+--------+--------+-------+ males.| over   |
+  |          |        | Eosin. | Fused. | Eosin  | Wild- |       | value. |
+  |          |        |        |        | fused. | type. |       |        |
+  +----------+--------+--------+--------+--------+-------+-------+--------+
+  |  56I     |  496   |   131  |   113  |  82    |  104  |   430 |   43   |
+  +----------+--------+--------+--------+--------+-------+-------+--------+
+
+{54}
+
+The data give 43 per cent of crossing-over, which places fused far to the
+right or to the left of eosin. The latter position is improbable, since
+eosin already lies very near the extreme left end of the known series.
+Therefore, since 43 per cent would place the factor nearly at the right end
+of the series, the next step was to test its relation to a factor like bar
+that lies at the right end of the chromosome. By mating to bar alone we
+could only get the linkage to bar without discovering on which side of bar
+the new factor lies, but by mating to a fly that carries still another
+sex-linked factor, known to lie to the left of bar, the information gained
+should show the relative order of the factors involved. Furthermore, since,
+by making a back-cross, both males and females give the same kind of data
+(and need not be separated), the experiment was made in this way. In order
+to have material for such an experiment double mutant stocks of vermilion
+fused and also of bar fused were made up.
+
+[Illustration: Fig. D.--_a_, normal wing; _b_ and _c_, fused wings. _c_
+shows a typical fused wing. The most striking feature is the closure of the
+cell between the third and fourth longitudinal veins with the elimination
+of the cross-vein; the veins at the base of the wing differ from those in
+the normal shown in a. _b_ shows the normal position in which the fused
+wings are held. The fusion of the veins in _b_ is unusually complete.]
+
+{55}
+
+LINKAGE OF VERMILION, BAR, AND FUSED.
+
+Males from the stock of (red) bar fused were mated to vermilion (not-bar,
+not-fused) females, and produced bar females and vermilion males. The bar
+F_1 daughters were back-crossed to vermilion fused males and produced the
+classes of offspring shown in table 34.
+
+TABLE 34.--P_1 _vermilion_ [female] [female] x _bar fused_ [male] [male].
+_B. C. F_1 bar_ [female] x _vermilion fused_ [male] [male].
+
+  +----------+-------------------+---------------------+------------------+
+  |          | v                 | v       B'      f_u | v            f_u |
+  |          | ----------------- | ----+-------------- | -----------+---- |
+  |          |         B'    f_u |                     |        B'        |
+  |Reference.+----------+--------+----------+----------+-----------+------+
+  |          |          |        | Vermilion|          |           |      |
+  |          |Vermilion.| Bar    | bar      |Wild-type.| Vermilion | Bar. |
+  |          |          | fused. | fused.   |          | fused.    |      |
+  +----------+----------+--------+----------+----------+-----------+------+
+  |140 I     |   137    |   130  |     35   |    40    |     5     |   8  ~
+  |141 I     |   144    |   137  |     38   |    41    |     4     |   2  ~
+  |142 I     |   153    |   120  |     43   |    58    |     6     |   7  |
+  |143 I     |   153    |    92  |     44   |    41    |     3     |   7  |
+  |145 I     |    69    |    62  |     29   |    19    |     1     |  ..  |
+  |146 I     |    96    |   103  |     30   |    34    |     7     |   3  |
+  |156 I     |    62    |    45  |     25   |    27    |     1     |   4  |
+  |157 I     |    93    |    57  |     11   |    31    |     2     |   2  |
+  |          +----------+--------+----------+----------+-----------+------+
+  |   Total. |   907    |   746  |    255   |   291    |    29     |  33  |
+  +----------+----------+--------+----------+----------+-----------+------+
+
+  +--------------------+--------+--------------------------------+
+  | v       B'         |        |                                |
+  | ----+--------+---- |        |      Cross-over values.        |
+  |                f_u |        |                                |
+  +-----------+--------+        +-----------+--------+-----------+
+  |           |        | Total. |           |        |           |
+  | Vermilion | Fused. |        | Vermilion | Bar    | Vermilion |
+  | bar.      |        |        | bar.      | fused. | fused.    |
+  +-----------+--------+--------+-----------+--------+-----------+
+  ~     ..    |   ..   |   355  |     21    |    4   |     25    |
+  ~     ..    |   ..   |   366  |     22    |    2   |     23    |
+  |      1    |   ..   |   388  |     26    |    4   |     29    |
+  |      3    |    1   |   344  |     26    |    4   |     28    |
+  |      1    |   ..   |   181  |     27    |    1   |     27    |
+  |     ..    |   ..   |   273  |     23    |    4   |     26    |
+  |     ..    |   ..   |   164  |     32    |    3   |     35    |
+  |     ..    |    2   |   198  |     22    |    3   |     23    |
+  +-----------+--------+--------+-----------+--------+-----------+
+  |      5    |    3   | 2,269  |     24    |    3   |     27    |
+  +-----------+--------+--------+-----------+--------+-----------+
+
+The data show that the factor for fused lies about 3 units to the right of
+bar. This is the furthest point yet obtained to the right. The reasons for
+locating fused to the right of bar are that, if it occupies such a
+position, then the double cross-over classes (which are expected to be the
+smallest classes) should be vermilion bar and fused, and these are, in
+fact, the smallest classes. The order of factors is, then, vermilion, bar,
+fused. This order is confirmed by the result that the number of cross-overs
+between fused and vermilion is greater than that between bar and vermilion.
+
+In order to obtain data to balance viability effects, the following
+experiment was made:
+
+Vermilion (not-bar) fused males were bred to (red) bar (not-fused) females.
+The daughters and sons were bar. The daughters were back-crossed, singly,
+to vermilion fused males and gave the results shown in table 35. Each
+female was also transferred to a second culture bottle, so that for each
+female there are two broods given consecutively (82, 82', etc.) in table
+35.
+
+The results given by the two broods of the same female are similar. The
+values are very near to those given in the last experiment, and confirm the
+conclusions there drawn. The combined data give the results shown in table
+36. {56}
+
+TABLE 35.--_P_1 bar [female] [female] x vermilion fused [male] [male]. B.
+C. F_1 bar [female] x vermilion fused [male] [male]._
+
+  A - Vermilion fused.
+  B - Bar.
+  C - Vermilion bar.
+  D - Fused.
+  E - Vermilion.
+  F - Bar fused.
+  G - Vermilion bar fused.
+  H - Wild type.
+
+  -------------------------------------------------------------------------
+            |   v   f_u   | v    B' |v        |v  B' f_u|      |  Cross-
+            |  --------   |----+----|----+----|-+---+---|      |   over
+            |     B'      |     f_u |  B' f_u |         |Total.|  values.
+  Reference +-------------+---------+---------+---------+      +-----------
+            |   A  |   B  | C  | D  | E  | F  | G  | H  |      | C | F | A
+  ----------+------+------+----+----+----+----+----+----+------+---+---+---
+            |      |      |    |    |    |    |    |    |      |   |   |
+    82      |  165 |  165 | 63 | 57 |  8 |  7 |  1 | .. |  466 | 26|3  | 29
+    82'     |  104 |   87 | 26 | 24 | .. |  4 | .. | .. |  245 | 20|2  | 22
+    83      |  128 |  164 | 51 | 39 |  6 |  4 | .. | .. |  392 | 23|3  | 26
+    83'     |  100 |   94 | 28 | 30 |  4 |  4 | .. | .. |  260 | 22|3  | 25
+    89      |   85 |  105 | 23 | 24 |  5 |  2 | .. | .. |  244 | 19|3  | 22
+    89'     |   78 |   91 | 21 | 27 |  1 |  2 | .. |  1 |  221 | 22|2  | 23
+    90      |   86 |   85 | 30 | 28 |  5 | .. | .. | .. |  234 | 25|2  | 27
+    90'     |   33 |   38 | 22 | 14 |  4 |  1 | .. |  1 |  113 | 33|5  | 36
+    91      |  125 |  107 | 41 | 31 |  1 |  1 | .. | .. |  306 | 24|1  | 24
+    91'     |   91 |   95 | 31 | 25 |  5 |  1 | .. |  2 |  250 | 23|3  | 25
+    92      |  109 |  136 | 41 | 24 |  4 |  2 | .. | .. |  316 | 21|2  | 23
+    92'     |  100 |  105 | 29 | 29 | .. |  1 | .. |  1 |  265 | 22|1  | 22
+    93      |   75 |   67 | 19 | 20 | .. |  1 | .. | .. |  182 | 21|1  | 22
+    93'     |   68 |   94 | 31 | 17 |  1 |  1 | .. | .. |  212 | 23|1  | 24
+    94      |   84 |   96 | 31 | 35 |  8 |  1 | .. | .. |  255 | 26|4  | 29
+    94'     |   61 |   73 | 20 | 22 |  5 |  4 | .. | .. |  185 | 23|5  | 28
+    95      |   84 |  102 | 27 | 26 |  3 |  3 | .. | .. |  245 | 22|2  | 24
+    96      |  144 |  148 | 43 | 34 |  1 |  2 | .. |  1 |  373 | 21|1  | 21
+    97      |   81 |   96 | 25 | 20 |  5 |  3 | .. | .. |  230 | 20|4  | 23
+    98      |  107 |  112 | 39 | 33 |  1 |  2 | .. | .. |  294 | 25|1  | 26
+    Firsts  |1,273 |1,383 |433 |371 | 47 | 28 |  1 |  1 |3,537 | 23|2  | 25
+    Seconds |  635 |  677 |208 |188 | 20 | 18 | .. |  5 |1,751 | 23|3  | 25
+  ----------+------+------+----+----+----+----+----+----+------+---+---+---
+      Total.|1,908 |2,060 |641 |559 | 67 | 46 |  1 |  6 |5,288 | 23|2.3| 25
+  ----------+------+------+----+----+----+----+----+----+------+---+---+---
+
+TABLE 36.--_Linkage of vermilion, bar, and fused with balanced viability._
+
+  +------------+----------+-----------+-----------+-----------+--------+
+  |            | v B' f_u | v         | v  B'     | v     f_u |        |
+  |            | -------- | --+------ | -----+--- | -+---+--- | Total. |
+  |            |          |    B' f_u |       f_u |    B'     |        |
+  +------------+----------+-----------+-----------+-----------+--------+
+  |            |          |           |           |           |        |
+  |            |   5,621  |   1,756   |    175    |    15     |  7,567 |
+  | Percentage |    74.3  |   23.19   |   2.31    |     0.2   |        |
+  |            |          |           |           |           |        |
+  +------------+----------+-----------+-----------+-----------+--------+
+
+Some additional data bearing on the linkage of vermilion and fused were
+obtained. Males of (red) fused stock were bred to vermilion (not-fused)
+females, and gave wild-type females and vermilion males, which inbred gave
+the results shown in table 37.
+
+The percentage of cross-overs between vermilion and fused is here 27, which
+is in agreement with the 26 per cent of the preceding experiment.
+
+The converse experiment, namely, red (not-fused) females by vermilion fused
+males also gave, when the wild-type daughters were {57} back-crossed to
+vermilion fused males, a linkage value of 27 units. Two 10-day broods were
+reared from each female. The data given in table 38 show that the
+percentage of crossing-over does not change as the flies get older. The
+locus of fused on the basis of all of the data is at 59.5.
+
+TABLE 37.--P_1 vermilion [female] [female] x fused [male] [male]. F_1
+wild-type [female] [female] x F_1 vermilion [male] [male].
+
+  KEY:
+  A: Non-cross-over [male] [male].
+  B: Cross-over [male] [male].
+  C: Females.
+  D: Vermilion.
+  E: Fused.
+  F: Vermilion fused.
+  G: Wild-type.
+  H: Total [male] [male].
+  I: Cross-over values.
+
+  +------------+-----+-----------+----------+-----+----+
+  |            |     |     A     |    B     |     |    |
+  |            |     +-----+-----+----+-----+     |    |
+  | Reference. |  C  |  D  |  E  | F  |  G  |  H  | I  |
+  +------------+-----+-----+-----+----+-----+-----+----+
+  | 79 I       | 299 |  93 |  96 | 37 |  36 | 262 | 28 |
+  | 80 I       | 245 |  93 |  60 | 28 |  27 | 208 | 26 |
+  | 81 I       | 263 | 101 |  63 | 22 |  40 | 226 | 27 |
+  |            +-----+-----+-----+----+-----+-----+----+
+  |   Total.   | 807 | 287 | 219 | 87 | 103 | 696 | 27 |
+  +------------+-----+-----+-----+----+-----+-----+----+
+
+TABLE 38.--P_1 wild [female] [female] x vermilion fused [male] [male]. F_1
+wild-type [female]    x F_1 wild-type [male] [male].
+
+  KEY:
+  A: Wild-type [female] [female].
+  B: Non-Cross-over [male].
+  C: Cross-over [male].
+  D: Vermilion fused.
+  E: Wild-type.
+  F: Vermilion.
+  G: Fused.
+  H: Total [male] [male].
+  I: Cross-over values.
+
+  +------------+-------+------------+-----------+-----+----+
+  |            |       |     B      |     C     |     |    |
+  |            |       +-----+------+-----+-----+     |    |
+  | Reference. |   A   |  D  |   E  |  F  |  G  |  H  | I  |
+  +------------+-------+-----+------+-----+-----+-----+----+
+  | 52         |    96 |  25 |   30 |  16 |  11 |  82 | 33 |
+  | 52'        |   176 |  59 |   64 |  24 |  19 | 166 | 26 |
+  | 53         |    60 |  20 |   22 |   9 |   6 |  57 | 26 |
+  | 53'        |    76 |  21 |   27 |  11 |  10 |  69 | 31 |
+  | 54         |    88 |  35 |   38 |  14 |  16 | 103 | 29 |
+  | 54'        |    60 |  22 |   20 |   8 |   9 |  59 | 29 |
+  | 57         |    61 |  22 |   20 |   7 |  11 |  60 | 30 |
+  | 57'        |   170 |  47 |   54 |  24 |  19 | 144 | 30 |
+  | 58         |   128 |  37 |   55 |  14 |  10 | 116 | 21 |
+  | 58'        |   144 |  38 |   64 |  16 |  15 | 133 | 23 |
+  | Firsts     |   433 | 139 |  165 |  60 |  54 | 418 | 27 |
+  | Seconds    |   626 | 187 |  229 |  83 |  72 | 571 | 27 |
+  |            +-------+-----+------+-----+-----+-----+----+
+  |   Total    | 1,059 | 326 |  394 | 143 | 126 | 989 | 27 |
+  +------------+-------+-----+------+-----+-----+-----+----+
+
+FORKED.
+
+On November 19, 1912 there appeared in a stock of a double recessive
+eye-color, vermilion maroon, a few males which showed a novel form of the
+large bristles (macrochaetae) upon the head and thorax. In this mutation
+(text-fig. E) the first of several which affect the shape and distribution
+of the bristles, the macrochaetae, instead of {58} being long, slender, and
+tapered (see Plate 1, fig. I), are greatly shortened and crinkled as though
+scorched. The ends are forked or branched, bent sharply, or merely
+thickened. The bristles which are most distorted are those upon the
+scutellum, where they are sometimes curled together into balls.
+
+LINKAGE OF VERMILION AND FORKED.
+
+[Illustration: FIG. E.--Forked bristles.]
+
+Since forked arose in vermilion stock, the double recessive for these two
+sex-linked factors could be used in testing the linkage relations of the
+mutation. Vermilion forked males were crossed to wild females and gave
+wild-type males and females, which inbred gave in F_2 the results shown in
+table 39. Forked reappeared only in the males in the following proportion:
+not-forked [female], 742; not-forked [male], 346; forked [male], 301. The
+result shows that the character is a sex-linked recessive.
+
+TABLE 39.--_P_1 wild_ [female] [female] x _vermilion-forked_ [male] [male].
+_F_1 wild-type_ [female] [female] x _F_1 wild-type_ [male] [male].
+
+  +----------+----------+----------------+---------------+--------+-------+
+  |          |          | Non-cross-over | Cross-over    |        |       |
+  |          |Wild-type | [male] [male]. | [male] [male].| Total  |Cross- |
+  |Reference.|[female]  +--------+-------+-------+-------+ [male] | over  |
+  |          |[female]. |  Ver-  |Wild-  | Ver-  |Forked.| [male].|values.|
+  |          |          | milion |type.  |milion.|       |        |       |
+  |          |          | forked.|       |       |       |        |       |
+  +----------+----------+--------+-------+-------+-------+--------+-------+
+  |  9 I     | 366      | 113    | 123   |  49   |  41   | 326    | 28    |
+  | 11 I     | 376      | 116    | 150   |  42   |  31   | 339    | 22    |
+  |          +----------+--------+-------+-------+-------+--------+-------+
+  |    Total.| 742      | 229    | 273   |  91   |  72   | 665    | 25    |
+  +----------+----------+--------+-------+-------+-------+--------+-------+
+
+In table 39 vermilion forked and wild-type are non-cross-overs, and
+vermilion and forked are cross-overs, giving a cross-over value of 25
+units. The locus, therefore, is 25 units to the right or to the left of
+vermilion, that is, either about 58 or 8 units from the yellow locus.
+
+LINKAGE OF CHERRY AND FORKED.
+
+Forked males were crossed to cherry females (cherry has the same locus as
+white, which is about 1 unit from yellow) and gave wild-type females and
+cherry males. These gave in F_2 the results shown in table 40. The
+non-cross-overs (cherry and forked) plus the cross-overs (cherry forked and
+wild type) divided into the cross-overs give a cross-over value of 46
+units, which shows that the locus lies to the right of vermilion, because
+if it had been to the left, the value would have been 8 (_i. e._, 33-25)
+instead of 33+25=58. The difference between 58 {59} and 46 is due to the
+expected amount of double crossing-over. In fact, for a distance as long as
+58 an almost independent behavior of linked gens is to be expected.
+
+TABLE 40.--_P_{1} cherry_ [female] [female] x _forked_ [male] [male].
+_F_{1} wild-type_ [female] [female] x _F_{1} cherry_ [male] [male].
+
+  +----------+--------------+---------------+-------------+-------+-------+
+  |Reference.|   Females.   | Non-cross-over|  Cross-over |       |       |
+  |          |              | [male] [male].|[male] [male]| Total |Cross- |
+  |          +-------+------+-------+-------+-------+-----+[male] | over  |
+  |          |Cherry.| Wild-|Cherry.|Forked.|Cherry |Wild-|[male].|values.|
+  |          |       | type.|       |       |forked.|type.|       |       |
+  +----------+-------+------+-------+-------+-------+-----+-------+-------+
+  | 25       |   129 |  145 |   73  |   70  |  65   |  68 |  276  |  48   |
+  | 25'      |   167 |  148 |   74  |   82  |  66   |  88 |  310  |  50   |
+  | 36       |    96 |   88 |   52  |   52  |  35   |  51 |  190  |  45   |
+  | 36'      |    57 |   76 |   41  |   32  |  24   |  30 |  127  |  43   |
+  | 84       |    76 |   86 |   40  |   34  |  38   |  26 |  138  |  46   |
+  | 84'      |    62 |   71 |   24  |   39  |  25   |  28 |  116  |  46   |
+  | 85       |   114 |   86 |   43  |   78  |  41   |  53 |  215  |  44   |
+  | 85'      |    98 |   95 |   48  |   63  |  52   |  46 |  209  |  47   |
+  | 86       |   307 |  323 |  152  |  144  | 118   | 165 |  579  |  49   |
+  | 87       |   351 |  341 |  183  |  213  | 160   | 147 |  703  |  45   |
+  | 88       |   244 |  246 |  142  |  142  | 107   | 104 |  495  |  43   |
+  +----------+-------+------+-------+-------+-------+-----+-------+-------+
+  |Total.    | 1,701 |1,705 |  872  |  949  | 731   | 806 |3,358  |  46   |
+  +----------+-------+------+-------+-------+-------+-----+-------+-------+
+
+LINKAGE OF FORKED, BAR, AND FUSED.
+
+This value of 58 gave the furthest locus to the right obtained up to that
+time, since forked is slightly beyond rudimentary. Later, the locus for
+bar-eye was found still farther to the right, and the locus for fused even
+farther to the right than bar. A cross was made involving these three gens.
+A forked (not-bar) fused male was bred to a (not-forked) bar (not-fused)
+female and gave bar females and males. The F_1 females were back-crossed
+singly to forked fused males with the result shown in table 41.
+
+TABLE 41.--_P_1 bar_ [female] [female] x _forked fused_ [male] [male]. _B.
+C. F_1 bar_ [female] x _forked fused_ [male] [male].
+
+  +-------+------------+-------------+--------------+-------------+-------+
+  |       |    f  f_u  |   f B'      |   f          |   f B' f_u  |       |
+  |Refer- |    ------  |  --+-----   |   ---+---    |   -+--+---  |       |
+  | ence. |      B'    |      f_u    |    B' f_u    |             |       |
+  |       +------+-----+------+------+-------+------+-------+-----+ Total.|
+  |       |Forked| Bar.|Forked|Fused.|Forked.| Bar  |Forked |Wild-|       |
+  |       |fused.|     | bar. |      |       |fused.|bar    |type.|       |
+  |       |      |     |      |      |       |      |fused. |     |       |
+  +-------+------+-----+------+------+-------+------+-------+-----+-------+
+  | 163   |  45  |  55 |  ..  |   1  |    4  |   2  |  ..   | ..  |  108  |
+  | 164   |  71  |  90 |  ..  |  ..  |    4  |   1  |  ..   | ..  |  166  |
+  | 165   |  97  | 106 |  ..  |  ..  |    2  |   4  |  ..   | ..  |  209  |
+  |  11   |  21  |  35 |  ..  |  ..  |    1  |   2  |  ..   | ..  |   59  |
+  |  33   |  15  |  23 |  ..  |  ..  |   ..  |   1  |  ..   | ..  |   39  |
+  |       +------+-----+------+------+-------+------+-------+-----+-------+
+  | Total.| 250  | 309 |  ..  |   1  |   11  |  10  |  ..   | ..  |  581  |
+  +-------+------+-----+------+------+-------+------+-------+-----+-------+
+
+{60}
+
+The same three points were combined in a different way, namely, by mating
+forked females to bar fused males. The bar daughters were back-crossed to
+forked fused males and gave the results shown in table 42.
+
+TABLE 42.--_P_1 forked_ [female] [female] x _bar fused_ [male] [male].
+_B.C. F_1 bar_ [female] x _forked fused_ [male] [male].
+
+  +------+--------------+-------------+-------------+--------------+------+
+  |      |    f         |  f B' f_u   |    f  f_u   |    f B'      |      |
+  |      |    ------    |  -+------   |    --+---   |    -+--+--   |      |
+  |Refer-|      B' f    |             |      B'     |        f_u   |Total.|
+  | ence.+-------+------+------+------+------+------+------+-------+      |
+  |      |Forked.| Fused|Forked| Wild-|Forked| Bar. |Forked| Fused.|      |
+  |      |       | bar. | bar  | type.|fused.|      |bar.  |       |      |
+  |      |       |      |fused.|      |      |      |      |       |      |
+  +------+-------+------+------+------+------+------+------+-------+------+
+  |158   | 131   |  124 |   1  |  ..  |  3   |   3  | ..   |  ..   |  262 |
+  |159   |  31   |   45 |  ..  |  ..  | ..   |  ..  | ..   |  ..   |   76 |
+  |160   |  29   |   23 |  ..  |  ..  |  1   |   2  | ..   |  ..   |   55 |
+  |161   |  24   |   11 |   1  |  ..  | ..   |  ..  | ..   |  ..   |   36 |
+  |162   |  96   |   91 |   2  |  ..  |  1   |   1  | ..   |  ..   |  191 |
+  |      +-------+------+------+------+------+------+------+-------+------+
+  |Total.| 311   |  294 |   4  |  ..  |  5   |   6  | ..   |  ..   |  620 |
+  +------+-------+------+------+------+------+------+------+-------+------+
+
+By combining the results of tables 41 and 42 data are obtained for
+cross-over values from which (by balancing the inviable classes, as
+explained in table 43) the element of inviability is reduced to a minimum.
+
+TABLE 43.
+
+  +----------+------------+------------+------------+------------+--------+
+  |          |            |            |            |            |        |
+  |          |   ------   |   -+----   |   ----+-   |   -+--+-   | Total. |
+  |          |            |            |            |            |        |
+  +----------+------------+------------+------------+------------+--------+
+  |          |            |            |            |            |        |
+  |          |   1,164    |     5      |     32     |     0      | 1,201  |
+  |Per cent. |    96.9    |    0.42    |     2.7    |     0      |        |
+  +----------+------------+------------+------------+------------+--------+
+
+The linkages involved in these data are very strong. The cross-overs
+between forked and bar number only 5 in a total of 1,201, which gives less
+than 0.5 per cent of crossing-over. There are 32 cross-overs or 2.7 per
+cent between bar and fused. The value for forked fused is the sum of the
+two other values, or 3.1 per cent.
+
+LINKAGE OF SABLE, RUDIMENTARY, AND FORKED.
+
+Rudimentary, forked, bar, and fused form a rather compact group at the
+right end of the chromosome, as do yellow, lethal 1, white, abnormal, etc.,
+at the zero end. The following two experiments were made to determine more
+accurately the interval between rudimentary and the other members of this
+group. A sable rudimentary forked {61} male mated to a wild female gave
+wild-type sons and daughters. These inbred give the results shown in table
+44.
+
+TABLE 44.--_P_{1} sable rudimentary forked_ [male] x _wild_ [female].
+_F_{1} wild-type_ [female] x _F_{1} wild-type_ [male] [male].
+
+  +----------+---------+-----------------+-------------------+
+  |          |         |     s  r f      |       s           |
+  |          |         |     ------      |       -+----      |
+  |          |         |                 |          r f      |
+  |          |         +-----------+-----+-------+-----------+
+  |Reference.|Wild-type|   Sable   |Wild-| Sable.|Rudimentary|
+  |          |[female] |rudimentary|type.|       |  forked.  |
+  |          |[female].|  forked.  |     |       |           |
+  +----------+---------+-----------+-----+-------+-----------+
+  |  264     |   98    |    28     | 17  |   2   |    5      ~
+  |  265     |   97    |    29     | 54  |   4   |    9      ~
+  |  266     |   114   |    42     | 49  |  11   |   11      |
+  +----------+---------+-----------+-----+-------+-----------+
+  |Total     |  309    |    99     |120  |  17   |   25      |
+  +----------+---------+-----------+-----+-------+-----------+
+
+  +----------+--------------------+--------------------+
+  |          |      s r           |      s    f        |
+  |          |      ---+-         |      -+--+-        |
+  |          |          f         |         r          |
+  |          +------------+-------+-------+------------+
+  |Reference.|   Sable    |Forked.|Sable  |Rudimentary.|
+  |          |rudimentary.|       |forked.|            |
+  |          |            |       |       |            |
+  +----------+------------+-------+-------+------------+
+  ~  264     |     1      |   1   |  ..   |   ..       |
+  ~  265     |    ..      |  ..   |  ..   |   ..       |
+  |  266     |    ..      |   2   |  ..   |   ..       |
+  +----------+------------+-------+-------+------------+
+  |Total     |     1      |   3   |  ..   |   ..       |
+  +----------+------------+-------+-------+------------+
+
+There were 265 males, of which 42 were cross-overs between sable and
+rudimentary and 4 between rudimentary and forked. The values found are:
+sable rudimentary, 16; rudimentary forked, 1.5; sable forked, 17.
+
+LINKAGE OF RUDIMENTARY, FORKED, AND BAR.
+
+The three gens, rudimentary, forked, and bar, form a very compact group. A
+rudimentary forked male was crossed to bar females and the daughters (bar)
+were back-crossed singly to rudimentary forked males, the results being
+shown in table 45.
+
+TABLE 45.--_P_1 rudimentary forked_ [male] x _bar_ [female]. _B.C. F_1 bar_
+[female] x _rudimentary forked_ [male] [male].
+
+  +----------+---------------+---------------+-------------+--------------+
+  |          |     r f       |     r   B'    |    r f B'   |     r        |
+  |          |     ------    |     -+----    |    ----+-   |     -+--+-   |
+  |          |         B'    |       f       |             |       f B'   |
+  |          +---------+-----+-------+-------+-------+-----+-------+------+
+  |Reference.| Rudim-  | Bar.| Rudim-|Forked.| Rudim-|Wild-| Rudim-|Forked|
+  |          | entary  |     | entary|       | entary|type.| entary| bar. |
+  |          | forked. |     |  bar. |       | forked|     |       |      |
+  |          |         |     |       |       |  bar. |     |       |      |
+  +----------+---------+-----+-------+-------+-------+-----+-------+------+
+  |267       |    56   | 104 |  ..   |   2   |   1   |  1  |   ..  |  ..  |
+  |268       |    82   |  86 |   1   |   2   |  ..   | ..  |   ..  |  ..  |
+  |269       |    68   | 101 |  ..   |  ..   |  ..   |  1  |   ..  |  ..  |
+  +----------+---------+-----+-------+-------+-------+-----+-------+------+
+  |Total     |   206   | 291 |   1   |   4   |   1   |  2  |   ..  |  ..  |
+  +----------+---------+-----+-------+-------+-------+-----+-------+------+
+
+The cross-over values are: rudimentary forked, 1; forked bar, 0.6;
+rudimentary bar, 1.6. The order of factors is rudimentary, forked, bar. On
+the basis of the total data the locus of forked is at 56.5. {62}
+
+SHIFTED.
+
+Shifted appeared (January 1913) in a stock culture of vermilion dot. The
+chief characteristic of this mutant is that the third longitudinal vein
+(see text-fig. F) does not reach the margin as it does in the normal fly.
+The vein is displaced toward the fourth throughout its length, and only
+very rarely does it extend far enough to join the marginal vein. The
+cross-vein between the third and the fourth veins is often absent because
+of the shifting. The flies themselves are smaller than normal. The wings
+are held out from the body at a wide angle. The two posterior bristles of
+the scutellum are much reduced in size and stick straight up--a useful
+landmark by which just-hatched shifted flies may be recognized, even though
+the wings are not expanded.
+
+LINKAGE OF SHIFTED AND VERMILION.
+
+Since shifted arose in vermilion, the double recessive shifted vermilion
+was available for the following linkage experiment: shifted vermilion males
+by wild females gave wild-type males and females which inbred gave the data
+shown in table 46.
+
+[Illustration: FIG. F.--Shifted venation. The third longitudinal vein is
+shifted toward the fourth and fails to reach the margin. Cross-vein between
+third and fourth longitudinal veins is lacking.]
+
+Disregarding the eye-color, the following is a summary of the preceding
+results: wild-type [female], 1,001; wild-type [male], 437; shifted [male],
+328. The result shows that shifted is a sex-linked recessive. The data of
+table 46 show that the locus of shifted lies about 15 units on one side or
+the other of vermilion, which from the calculated position of vermilion at
+33 would give a position for shifted at either 18 or 48 from yellow.
+
+TABLE 46.--_P_1 shifted vermilion [male] [male] x wild [female] [female].
+F_1 wild-type [female] x F_1 wild-type [male] [male]._
+
+  Key to columns:
+
+  A:  Wild-type [female] [female].
+  B:  Non-cross-over [male] [male], Shifted.
+  C:  Non-cross-over [male] [male], Wild-type.
+  D:  Cross-over [male] [male], Shifted.
+  E:  Cross-over [male] [male], Wild-type.
+  F:  Total [male] [male].
+  G:  Cross-over values.
+
+  +--------------+---------+------+------+-------+-------+-------+------+
+  | Reference.   |     A   |  B   |  C   |  D    |  E    |   F   |  G   |
+  +--------------+---------+------+------+-------+-------+-------+------+
+  | 13           |    345  |  79  | 115  |   8   |  25   |  227  |  15  |
+  | 29           |     68  |  20  |  32  |   3   |   4   |   59  |  12  |
+  | 30           |    191  |  37  |  54  |   5   |  13   |  109  |  17  |
+  | 31           |    151  |  41  |  65  |  17   |  13   |  136  |  22  |
+  | 33           |    133  |  49  |  40  |   4   |   6   |   99  |  10  |
+  | 34           |    113  |  56  |  59  |   9   |  11   |  135  |  15  |
+  +--------------+---------+------+------+-------+-------+-------+------+
+  |  Total.      |   1,001 | 282  |  365 |   46  |   72  |  765  |  15  |
+  +--------------+---------+------+------+-------+-------+-------+------+
+
+{63}
+
+LINKAGE OF SHIFTED, VERMILION, AND BAR.
+
+In order to determine on which side of vermilion shifted lies, a shifted
+vermilion (not-bar) female was crossed to a (not-shifted red) bar male.
+Three factors are involved, of which one, bar, is dominant. The shifted
+vermilion (not-bar) stock is a triple recessive, and a three-point
+back-cross was therefore possible. The daughters were bar and the sons were
+shifted vermilion (the triple recessive). Inbred these gave the results
+shown in table 46. The smallest classes (double cross-overs) are shifted
+and vermilion bar, which places shifted to the left of vermilion at
+approximately 17.8 units from yellow.
+
+TABLE 47.--_P_1 shifted vermilion_ [female] x _bar_ [male] [male]. _F_1
+bar_ [female] x _F_1 shifted vermillion_ [male] [male].
+
+  +-------+---------------+---------------+---------------+---------------+
+  |       |    s_h  v     |    s_h  B'    |   s_h v B'    |    s_h        |
+  | Refer-|    ------     |    --+----    |    -----+-    |    --+-+--    |
+  | ence. |        B'     |       v       |               |       v B'    |
+  |       +----------+----+--------+------+---------+-----+--------+------+
+  |       |Shifted   |Bar.|Shifted |Verm- |Shifted  |Wild-|Shifted.| Verm-~
+  |       |vermilion.|    |  bar.  |ilion.|vermilion|type.|        | ilion~
+  |       |          |    |        |      |bar.     |     |        | bar. |
+  +-------+----------+----+--------+------+---------+-----+--------+------+
+  |  65   |  56      |108 |   15   |  20  |  8      | 33  |  1     |  1   |
+  +-------+----------+----+--------+------+---------+-----+--------+------+
+
+  +----------+------+----------------------------+
+  |          |      |                            |
+  |Reference.|Total.| Cross-over values.         |
+  |          |      |                            |
+  |          |      +----------+---------+-------+
+  ~          |      |Shifted   |Vermilion|Shifted|
+  ~          |      |vermilion.|bar.     |bar.   |
+  |          |      |          |         |       |
+  +----------+------+----------+---------+-------+
+  | 65       | 242  |  15      | 18      |  31   |
+  +----------+------+----------+---------+-------+
+
+The stock of shifted has been thrown away, since too great difficulty was
+encountered in maintaining it, because, apparently, of sterility in the
+females.
+
+LETHALS SA AND SB.
+
+The first lethal found by Miss Rawls was in a stock that had been bred for
+about 3 years. While there was no _a priori_ reason that could be given to
+support the view that lethal mutations would occur more frequently among
+flies inbred in confinement, nevertheless a hundred females from each of
+several newly caught and from each of several confined stocks were examined
+for lethals (Stark, 1915). No lethals were found among the wild stocks, but
+4 were found among the confined stocks. Whether this difference is
+significant is perhaps open to question. The first lethal was found in
+January 1913, in a stock that had been caught at Falmouth, Massachusetts,
+in 1911, and had been inbred for 18 months, _i.e._, for about 50
+generations. This lethal, lethal _sa_, was recessive and behaved like the
+former lethals, being transmitted by half the females and causing the death
+of half the sons. The position of this lethal to the X chromosome was found
+as follows, by means of the cross-over value white lethal _sa_.
+Lethal-bearing females were mated to white males and the lethal-bearing
+daughters were again mated to white males. The white sons (894) were
+non-cross-overs and the red sons (256) were cross-overs. The percentage of
+crossing-over {64} is 22.2. A correction of 0.4 unit should be added for
+double crossing-over, indicating that the locus is 22.6 units from white,
+or at 23.7.
+
+When the work on lethal _sa_ had been continued for 3 months, the second
+lethal, lethal _sb_, was found (April 1913) to be present in a female which
+was already heterozygous for lethal _sa_. It is probable that this second
+lethal arose as a mutation in the father, and that a sperm whose X carried
+lethal _sb_ fertilized an egg whose X carried lethal _sa_. As in the cases
+of lethals 1 and 1_a_ and lethals 3 and 3_a_, this lethal, lethal _sb_, was
+discovered from the fact that only a very few sons were produced, there
+being 82 daughters and only 3 sons. If, as in the other cases, the number
+of daughters is taken as the number of non-cross-overs and twice the number
+of sons as the cross-overs, it is found that the two lethals are about 7
+units apart. Since the two lethals were in different X chromosomes, all the
+daughters should receive one or the other lethal, except in those few cases
+in which crossing over had taken place. Of the daughters 19 were tested and
+every one was found to carry a lethal. Again, if the cross-over values of
+the lethals with some other character, such as white eyes, be found and
+plotted, the curve should show two modes corresponding to the two lethals.
+This test was applied, but the curve failed to show two modes clearly,[7]
+the two lethals being too close together to be differentiated by the small
+number of determinations that were made. It seems probable that lethal _sa_
+and lethal _sb_ are about 5 units apart.
+
+The position of lethal _sb_ was accurately found by continuing the
+determinations with a white lethal cross-over. A white female was found
+which had only one of the two lethals and the linkage of this lethal with
+eosin and miniature was found as follows: A female carrying white and
+lethal in one chromosome and no mutant factor in the homologous chromosome
+was bred to an eosin miniature male. The white eosin daughters carried
+lethal, and their sons show the amount of crossing-over between white and
+lethal (15.6), between lethal and miniature (19.9), and between white and
+miniature (32.9). The data on which these calculations are based are given
+in table 48.
+
+TABLE 48.--_Data on the linkage of white, lethal sb, and miniature, from
+Stark, 1915_.
+
+  +-----------+------------+------------+--------------+
+  | w^e     m | w^e l_{sb} | w^e        | w^e l_{sb} m |
+  | --------- | ---+------ | -------+-- | ---+-----+-- |
+  | w l_{sb}  | w        m | w l_{sb} m | w            |
+  |           |            |            |              |
+  +-----------+------------+------------+--------------+
+  | Eosin     | White      | Eosin.     | White.       ~
+  | miniature | miniature. |            |              ~
+  |           |            |            |              |
+  +-----------+------------+------------+--------------+
+  | 2,421     | 524        | 685        | 48           |
+  +-----------+------------+------------+--------------+
+
+  +--------+--------------------------------+
+  |        |                                |
+  |        |       Cross-over values.       |
+  |        |                                |
+  |        |                                |
+  | Total. +----------+----------+----------+
+  ~        |White     |Lethal    |White     |
+  ~        |lethal    |_sb_      |miniature.|
+  |        |_sb_.     |miniature.|          |
+  +--------+----------+----------+----------+
+  | 3,678  | 15.6     | 19.9     | 32.9     |
+  +--------+----------+----------+----------+
+
+{65}
+
+The locus of this lethal is at 16.7; the locus of lethal _sa_ was found to
+be at 23.7, so that the lethal at 16.7 is evidently the second lethal or
+lethal _sb_ whose advent gave rise to the high sex-ratio. This
+interpretation is in accord with the curve which Miss Stark published, for
+although the mode which corresponds to lethal _sa_ is weak, the mode at
+15-16 is well marked.
+
+The two other lethals, lethals _sc_ and _sd_, which came up in the course
+of these experiments by Miss Stark, are treated in other sections of this
+paper.
+
+BAR.
+
+(Plate II, figures 12 and 13.)
+
+The dominant sex-linked mutant called bar-eye (formerly called barred)
+appeared in February 1913 in an experiment involving rudimentary and
+long-winged flies (Tice, 1914). A female that is heterozygous for bar has
+an eye that is intermediate between the rounded eye of the wild fly and the
+narrow band of the bar stock. This heterozygous bar female is always
+readily distinguishable from the normal, but can not always be separated
+from the pure bar. Bar is therefore nearly always used as a dominant and
+back-crosses are made with normal males.
+
+Bar is the most useful sex-linked character so far discovered, on account
+of its dominance, the certainty of its classification, and its position
+near the right end of the X chromosome. The locus of bar at 57 was
+determined on the basis of the data of table 65.
+
+NOTCH.
+
+A sex-linked dominant factor that brings about a notch at the ends of the
+wings appeared in March 1913, and has been described and figured by Dexter
+(1914, p. 753, and fig. 13, p. 730). The factor acts as a lethal for the
+male. Consequently a female heterozygous for notch bred to a wild male
+gives a 2:1 sex-ratio; half of her daughters are notch and half normal; the
+sons are only normal. The actual figures obtained by Dexter were 235 notch
+females, 270 normal females, and 235 normal males.
+
+The location of notch in the X chromosome was not determined by Dexter, but
+the mutant has appeared anew three or four times and the position has been
+found by Bridges to be approximately at 2.6. {66}
+
+DEPRESSED.
+
+Several mutations have appeared in which the wings are not flat. Of these
+the first that appeared was curved (second chromosome), in which the wings
+are curved downward throughout their length, but are elevated and held out
+sidewise from the body; the texture is thinner than normal. The second of
+these wing mutants to appear was jaunty (second chromosome), in which the
+wings turn up sharply at the tip; they lie in the normal position. The
+third mutant, arc (second chromosome), has, as its name implies, its wings
+curved like the arc of a circle. The fourth mutant, bow (first chromosome,
+fig. C), is like arc, but the amount of curvature is slightly less. The
+fifth mutant, depressed (first chromosome, fig. G), has the tip of its
+wings turned down instead of up, as in jaunty, but, as in jaunty, the wing
+is straight, except near the tip, where it bends suddenly. These stocks
+have been kept separate since their origin, and flies from them have seldom
+been crossed to each other, because in the succeeding generations it would
+be almost impossible to make a satisfactory classification of the various
+types. But that they are genetically different mutations is at once shown
+on crossing any two, when wild-type offspring are produced. For instance,
+bow and arc are the two most nearly alike. Mated together (bow [male] by
+arc [female]), they give in F_1 straight-winged flies which inbred give in
+F_2 9 straight to 7 not-straight (_i.e._, bow, arc, and bow arc together).
+
+Depressed wings first appeared (April 1913) among the males of a culture of
+black flies. They were mated to their sisters and from subsequent
+generations both males and females with depressed wings were obtained which
+gave a pure stock. This new character proved to be another sex-linked
+recessive.
+
+LINKAGE OF DEPRESSED AND BAR.
+
+Depressed (not-bar) males mated to (not-depressed) bar females gave bar
+daughters. Two of these were back-crossed singly to depressed males and
+gave the results shown in table 49. Males and females were not separated,
+since they should give the same result.
+
+TABLE 49.--_P_1 depressed_ [female] [female] x _bar_ [female] [female].
+_B.C. F_1 bar_ [female] x _depressed_ [male] [male].
+
+  +----------+--------------------+-------------------+-------+-----------+
+  |          | Non-cross-overs.   | Cross-overs.      |       |           |
+  +----------+-------------+------+-----------+-------+       |           |
+  |Reference.|  Depressed. | Bar. | Depressed | Wild- | Total.| Cross-over|
+  |          |             |      | bar.      | type. |       | values.   |
+  +----------+-------------+------+-----------+-------+-------+-----------+
+  | 66 I     |    48       |   51 |   21      |   41  |  161  |   39      |
+  | 67 I     |    85       |  104 |   44      |   70  |  303  |   38      |
+  +----------+-------------+------+-----------+-------+-------+-----------+
+  |    Total.|   133       |  155 |   65      |  111  |  464  |   38      |
+  +----------+-------------+------+-----------+-------+-------+-----------+
+
+{67}
+
+[Illustration: FIG. G.--Depressed wing.]
+
+LINKAGE OF CHERRY, DEPRESSED, AND VERMILION.
+
+The linkage value 38 (see table 49) indicates that depressed is somewhere
+near the opposite end of the series of sex-linked factors from bar. The
+locus could be more accurately determined by finding the linkage relations
+of depressed with gens at its end of the chromosome. Accordingly, depressed
+females were crossed to cherry vermilion males. F_1 gave wild-type females
+and depressed males. The daughters bred again to cherry vermilion males
+gave the results shown in table 50. The data only suffice to show that the
+locus of depressed is about midway between cherry and vermilion, or at
+about 15 units from yellow.
+
+The F_1 males in the last experiment did not have their wings as much
+depressed as is the condition in stock males, and in F_2 most of the
+depressed winged males were of the F_1 type, although a few were like those
+of stock. This result suggests that the stock is a double recessive,
+_i. e._, one that contains, in addition to the sex-linked depressed, an
+autosomal factor that intensifies the effect of the primary sex-linked
+factor.
+
+TABLE 50.--_P_1 depressed [female] x cherry vermilion [male] [male]._
+
+  +-------------------++---------------------------------------+
+  |                   ||             Second generation.        |
+  |       First       |+----------+--------+-------------------+
+  |    generation.    ||          |        |       w^c  v      |
+  +---------|---------+|          |        |      -------      |
+  |         |         ||          |        |        d_p        |
+  |  Wild-  |Depressed||          |        +---------+---------+
+  |  type   | [male]  ||Reference.|        |         |         ~
+  |[female] | [male]. ||          |[female]|Cherry   |         ~
+  |[female].|         ||          |[female]|vermilion|Depressed|
+  |         |         ||          |        |         |         |
+  |         |         ||          |        | [male]. | [male]. |
+  +---------+---------++----------+--------+---------+---------+
+  |   21    |    31   ||     19 I |   59   |     23  |   24    |
+  +---------+---------++----------+--------+---------+---------+
+
+  +---------------------------------------------------------+
+  |                  Second generation.                     |
+  +-------------------+-------------------------------------+
+  |     w^c d_p       |     w^c          |    w^c d_p  v    |
+  |     --+-----      |     -----+--     |   --+----+---    |
+  |            v      |       d_p  v     |                  |
+  +---------+---------+--------+---------+---------+--------|
+  ~         |         |        |         |         |        |
+  ~ Cherry  |         | Cherry |Depressed|Cherry   | Wild-  |
+  |depressed|Vermilion|        |vermilion|depressed| type   |
+  |         |         |        |         |vermilion|        |
+  | [male]. |[male].  |[male]. | [male]. | [male]. | [male].|
+  +---------+---------+--------+---------+---------+--------+
+  |    6    |    6    |   5    |    5    |      0  |    0   |
+  +---------+---------+--------+---------+---------+--------+
+
+{68}
+
+CLUB.
+
+In May 1913 there were observed in a certain stock some flies which,
+although mature, did not unfold their wings (text-fig. H_a_). This
+condition was at first found only in males and suspicion was aroused that
+the character might be sex-linked. When these males were bred to wild
+females the club-shaped wings reappeared only in the F_2 males, but in
+smaller number than expected for a recessive sex-linked character. The
+result led to the further suspicion that not all those individuals that are
+genetically club show club somatically. These points are best illustrated
+and proven by the following history of the stock:
+
+[Illustration: FIG. H.--Club wing. _a_ shows the unexpanded wings of club
+flies; _c_ shows the absence of the two large bristles from the side of the
+thorax present in the normal condition of the wild, b.]
+
+Club females were obtained by breeding F_2 club males to their F_2
+long-winged sisters, half of which should be heterozygous for club. {69}
+5,352; wild-type [male], 4,181; club [male], 236. The wild-type males
+include, of course, those club males that have expanded wings (potential
+clubs).
+
+Club females by wild males gave in the F_2 generation (mass cultures):
+wild-type [female], 1,131; wild-type [male], 897; club [female], 57; club
+[male], 131.
+
+It is noticeable that there were fewer club females than club males,
+equality being expected, which might appear to indicate that the club
+condition is more often realized by the male than by the female, but later
+crosses show that the difference here is not a constant feature of the
+cross.
+
+Long-winged males from club stock (potential clubs) bred to wild females
+gave in F_2 the following: wild-type [female], 521; wild-type (and
+potential club) [male], 403; club [male], 82.
+
+Club females by club males of club stock gave in F_2: potential club
+[female], 126; potential club [male], 78; club [female], 95; club [male],
+81. These results are from 8 pairs. The high proportion of club is
+noticeable.
+
+Potential club females and males from pure club stock (_i. e._, stock
+derived originally from a pair of club) gave in F_2 the following:
+potential club [female], 1,049; potential club [male], 666; club [female],
+450; club [male], 453.
+
+GENOTYPIC CLUB.
+
+Accurate work with the club character was made possible by the discovery of
+a character that is a constant index of the presence of homozygous club.
+This character is the absence of the two large bristles (text-fig. H_c_)
+that are present on each side of the thorax of the wild fly as shown in
+figure Hb. All club flies are now classified by this character and no
+attention is paid to whether the wings remain as pads or become expanded.
+
+LINKAGE OF CLUB AND VERMILION.
+
+The linkage of club and vermilion is shown by the cultures listed in table
+51, which were obtained as controls in working with lethal III. The
+cross-over value is shown in the male classes by the cross-over fraction
+276/1463 or 19 per cent.
+
+LINKAGE OF YELLOW, CLUB, AND VERMILION.
+
+The data just given in table 51 show that club is 19 units from vermilion,
+but in order to determine in which direction from vermilion it lies, the
+crossing-over of club to one other gen must be tested. For this test we
+used yellow, which lies at the extreme left of the chromosome series. At
+the same time we included vermilion, so that a three-point experiment was
+made.
+
+Females that were (gray) club vermilion were bred to yellow (not-club red)
+and gave wild-type daughters and club vermilion sons. These inbred gave the
+results of table 52.
+
+The data from the males show that the locus of club is about midway between
+yellow and vermilion. This conclusion is based on the {70} evidence that
+yellow and club give 18 per cent of crossing-over, club and vermilion 20
+per cent, and yellow and vermilion 35 per cent. The double cross-overs on
+this view are yellow club (3) and vermilion (3). The females furnish
+additional data for the linkage of club and vermilion. The value calculated
+from the female classes alone is 20 units, which is the same value as that
+given by the males.
+
+TABLE 51.--_P_1 club_ [female] [female] x _vermilion_ [male] [male]. _F_1
+wild-type_ [female] x _F_1 club_ [male].
+
+  +----------+--------+-----------------+-----------------+-------+-------+
+  |          |        | Non-cross-over  | Cross-over      |       |       |
+  |          |        | [male] [male].  | [male] [male].  |       |       |
+  |          |        +------+----------+----------+------+ Total |Cross- |
+  |Reference.|Females.| Club.|Vermilion.|Club      |Wild- |[male] | over  |
+  |          |        |      |          |Vermilion.|type. |[male].|values.|
+  |          |        |      |          |          |      |       |       |
+  +----------+--------+------+----------+----------+------+-------+-------+
+  | 137      |    75  |  17  |    39    |      6   |  11  |    73 |  23   |
+  | 138      |    64  |  24  |    32    |      6   |   8  |    70 |  20   |
+  | 139      |    56  |  10  |    31    |      4   |   3  |    48 |  15   |
+  | 140      |    74  |  13  |    39    |      3   |   5  |    60 |  13   |
+  | 144      |    97  |  30  |    40    |     10   |  13  |    93 |  25   |
+  | 145      |    63  |  15  |    29    |      4   |   6  |    54 |  19   |
+  | 146      |   126  |  44  |    46    |      9   |   9  |   108 |  15   |
+  | 106      |    92  |  33  |    34    |      6   |  10  |    83 |  19   |
+  | 107      |    55  |  31  |    25    |      7   |   3  |    66 |  15   |
+  | 108      |    86  |  29  |    32    |      7   |  10  |    78 |  22   |
+  | 109      |   103  |  25  |    36    |      4   |   9  |    74 |  18   |
+  |          |    83  |  30  |    34    |      6   |   9  |    79 |  19   |
+  |          |    77  |  18  |    26    |      7   |   8  |    59 |  25   |
+  |          |    67  |  20  |    21    |      6   |   7  |    54 |  24   |
+  |          |   126  |  32  |    60    |     15   |  13  |   120 |  23   |
+  |          |    63  |  21  |    28    |      7   |  10  |    66 |  26   |
+  |          |   114  |  45  |    71    |      9   |   7  |   132 |  12   |
+  |          |    46  |  18  |    18    |      3   |   3  |    42 |  14   |
+  |          |   111  |  35  |    56    |      6   |   7  |   104 |  13   |
+  |          +--------+------+----------+----------+------+-------+-------+
+  |    Total.| 1,578  | 490  |   697    |    125   | 151  | 1,463 |  19   |
+  +----------+--------+------+----------+----------+------+-------+-------+
+
+TABLE 52.--_P_1 club vermilion_ [female] [female] x _yellow_ [male] [male].
+_F_1 wild-type_ [female] [female] x _F_1 club vermilion_ [male] [male].
+
+  +------------+-----------------------------------+
+  |            | F_2 females.                      |
+  |            +-----------------+-----------------+
+  |            | Non-cross-overs.|  Cross-overs.   |
+  |            |                 |                 |
+  |            |                 |                 |
+  |Reference.  +-----------+-----+------+----------+
+  |            | Club      |Wild-| Club.|Vermilion.~
+  |            | vermilion.|type.|      |          ~
+  +------------+-----------+-----+------+----------+
+  |  99        |    44     | 52  |  13  |    7     |
+  | 100        |    38     | 58  |   6  |   12     |
+  | 101        |    30     | 32  |   6  |   12     |
+  | 102        |    44     | 55  |  20  |   13     |
+  | 103        |   ...     |...  |  ... |   ...    |
+  |            +-----------+-----+------+----------+
+  |    Total.  |   156     |197  |  45  |   44     |
+  +------------+-----------+-----+------+----------+
+
+  +-----------------------------------------------------------------------+
+  |       F_2 males.                                                      |
+  +------------------+-----------------+----------------+-----------------+
+  |     y            |       y c_l v   |      y   v     |      y  c_l     |
+  |     ------       |       -+-----   |      ---+-     |      -+--+-     |
+  |     c_l  v       |                 |       c_l      |           v     |
+  +-------+----------+-----------+-----+----------+-----+------+----------+
+  ~Yellow.|Club      |Yellow club|Wild-|Yellow    |Club.|Yellow|Vermilion.|
+  ~       |vermilion.|vermilion. |type.|vermilion.|     |club. |          |
+  +-------+----------+-----------+-----+----------+-----+------+----------+
+  |  35   |   27     |    2      |  9  |    8     |  11 |   0  |     1    |
+  |  43   |   23     |    1      | 15  |   11     |  14 |   0  |     0    |
+  |  19   |   24     |    6      |  5  |   10     |   3 |   1  |     0    |
+  |  48   |   38     |   12      | 14  |    8     |  15 |   1  |     1    |
+  |  43   |   32     |    7      | 16  |   13     |   7 |   1  |     1    |
+  +-------+----------+-----------+-----+----------+-----+------+----------+
+  | 188   |  144     |   28      | 59  |   50     |  50 |   3  |     3    |
+  +-------+----------+-----------+-----+----------+-----+------+----------+
+
+{71}
+
+LINKAGE OF CHERRY, CLUB, AND VERMILION.
+
+The need for a readily workable character whose gen should lie in the long
+space between cherry and vermilion has long been felt. Cherry and vermilion
+are so far apart that there must be considerable double crossing-over
+between them. But with no favorably placed character which is at the same
+time viable and clearly and rapidly distinguishable, we were unable to find
+the exact amount of double crossing-over, and hence could not make a proper
+correction in plotting the chromosome. Club occupies just this favorable
+position nearly midway between cherry and vermilion. The distances from
+cherry to club and from club to vermilion are short enough so that no error
+would be introduced if we ignored the small amount of double crossing-over
+within each of these distances.
+
+It thus becomes important to know very exactly the cross-over values for
+cherry club and club vermilion. The experiment has the form of the yellow
+club vermilion cross of table 52, except that cherry is used instead of
+yellow. Cherry is better than yellow because it is slightly nearer club
+than is yellow and because the bristles of yellow flies are very
+inconspicuous. In yellow flies the bristles on the side of the thorax are
+yellowish brown against a yellow background, while in gray-bodied flies the
+bristles are very black against a light yellowish-gray background.
+
+For the time being we are able to present only incomplete results upon this
+cross. In the first experiment cherry females were crossed to club
+vermilion males and the wild-type daughters were back-crossed to cherry
+club vermilion, which triple recessive had been secured for this purpose.
+Table 53 gives the results.
+
+TABLE 53.--_P_{1} cherry_ [female] [female] x _club vermilion_ [male]
+[male]. _B. C. F__{1} _wild-type_ [female] x _cherry club vermilion_ [male]
+[male].
+
+  +--------+-------------------+-------------------+-------------------+
+  |        |  w^c              |  w^c   c_l     v  |  w^c           v  |
+  |        |  ---------------  |  ----+----------  |  -----------+---  |
+  | Refer- |       c_l      v  |                   |        c_l        |
+  | ence.  +-------------------+---------+---------+-------------------+
+  |        |         |         |         |         |         |         |
+  |        |         | Club    | Cherry  |         | Cherry  |         |
+  |        | Cherry. | ver-    | club    |  Wild-  | ver-    |  Club.  |
+  |        |         | milion. | ver-    |  type.  | milion. |         |
+  |        |         |         | milion. |         |         |         |
+  +--------+---------+---------+---------+---------+---------+---------+
+  |        |         |         |         |         |         |         ~
+  |  163   |    68   |    68   |     4   |    10   |    21   |    13   ~
+  |  164   |    99   |    67   |    13   |    21   |    21   |    12   |
+  |  165   |    23   |    37   |     9   |     7   |    15   |     2   |
+  |  166   |   107   |    86   |    14   |    28   |    31   |    43   |
+  |  167   |    42   |    49   |     7   |    11   |    12   |    11   |
+  |  168   |    40   |    30   |     6   |    15   |    16   |     8   |
+  |        +---------+---------+---------+---------+---------+---------+
+  | Total. |   379   |   337   |    53   |    92   |   116   |    89   |
+  +--------+---------+---------+---------+---------+---------+---------+
+
+  +-------------------+---------+----------------------------+
+  |  w^c   c_l        |         |                            |
+  |  ----+------+---  |         |     Cross-over values.     |
+  |                v  |         |                            |
+  +---------+---------+         +----------------------------+
+  |         |         |         |        |         |         |
+  |         |         | Total.  |        | Club.   | Cherry  |
+  | Cherry  | Ver-    |         | Cherry | ver-    | ver-    |
+  | club.   | milion. |         | club.  | milion. | milion. |
+  |         |         |         |        |         |         |
+  +---------+---------+---------+--------+---------+---------+
+  ~         |         |         |        |         |         |
+  ~    1    |    0    |   185   |    8   |   19    |    26   |
+  |    1    |    0    |   234   |   15   |   15    |    29   |
+  |    0    |    2    |    95   |   19   |   25    |    35   |
+  |    3    |    3    |   315   |   15   |   25    |    37   |
+  |    2    |    2    |   136   |   16   |   20    |    30   |
+  |    0    |    0    |   115   |   18   |   21    |    39   |
+  +---------+---------+---------+--------+---------+---------+
+  |    7    |    7    | 1,080   |   15   |   20    |    32   |
+  +---------+---------+---------+--------+---------+---------+
+
+{72}
+
+A complementary experiment was made by crossing cherry club vermilion
+females to wild males and inbreeding the F_1 in pairs. Table 54 gives the
+results of this cross.
+
+TABLE 54.--_P_{1} cherry club vermilion_ [male] [male]. [female] [female] x
+_wild_ [male] [male]. _F_{1} wild-type_ [female] x _F_{1} cherry club
+vermilion_ [male] [male].
+
+  +----------+-----------------+------------------+-----------------+
+  |          |  w^c   c_l   v  |  w^c             |  w^c  c_l       |
+  |          |  -------------  |  ----+--------   |  ---------+---  |
+  |          |                 |        c_l   v   |              v  |
+  |          +-----------+-----+-------+----------+------+----------+
+  |Reference.|Cherry club|Wild-|Cherry.|  Club    |Cherry|Vermilion.|
+  |          |vermilion. |type.|       |vermilion.| club.|          |
+  +----------+-----------+-----+-------+----------+------+----------+
+  | 188      |    60     |  76 |  12   |    8     |  12  |   29     ~
+  | 189      |   228     | 314 |  48   |   44     |  50  |   60     ~
+  | 197      |    68     |  81 |  23   |   13     |   9  |   22     |
+  +----------+-----------+-----+-------+----------+------+----------+
+  |Total.    |   356     | 471 |  83   |   65     |  71  |  111     |
+  +----------+-----------+-----+-------+----------+------+----------+
+
+  +----------------+------+----------------------------+
+  |  w^c         v |      |                            |
+  |  ----+----+--- |      |     Cross-over values.     |
+  |       c_l      |      |                            |
+  +----------+-----+Total.+------+----------+----------+
+  |  Cherry  |Club.|      |Cherry|Club      |Cherry    |
+  |vermilion.|     |      |club. |vermilion.|vermilion.|
+  +----------+-----+------+------+----------+----------+
+  ~    2     |  1  |  200 |  11  |   22     |  30      |
+  ~    1     |  8  |  753 |  13  |   16     |  27      |
+  |    2     |  0  |  218 |  17  |   15     |  31      |
+  +----------+-----+------+------+----------+----------+
+  |    5     |  9  |1,171 |  14  |   17     |  28      |
+  +----------+-----+------+------+----------+----------+
+
+The combined data of tables 53 and 54 give 14.2 as the value for cherry
+club. All the data thus far presented upon club vermilion (886 cross-overs
+in a total of 4,681), give 19.2 as the value for club vermilion. The locus
+of club on the basis of the total data available is at 14.6.
+
+GREEN.
+
+In May 1913 there appeared in a culture of flies with gray body-color a few
+males with a greenish-black tinge to the body and legs. The trident pattern
+on the thorax, which is almost invisible in many wild flies, was here quite
+marked. A green male was mated to wild females and gave in F_2 a close
+approach to a 2:1:1 ratio. The green reappeared only in the F_2 males, but
+the separation of green from gray was not as easy or complete as desirable.
+From subsequent generations a pure stock of green was made. A green female
+by wild male gave 138 wild-type females and 127 males which were greenish.
+This green color varies somewhat in depth, so that some of these F_1 males
+could not have been separated with certainty from a mixed culture of green
+and gray males.
+
+The results of these two experiments show that green is a sex-linked
+melanistic character like sable, but the somatic difference produced is
+much less than in the case of sable, so that the new mutation, although
+genetically definite, is of little practical value. We have found several
+eye-colors which differed from the red color of the wild fly by very small
+differences. With some of these we have worked successfully by using
+another eye-color as a developer. For example, the double recessive
+vermilion "clear" is far more easily distinguished from vermilion than is
+clear from red. But it is no small task to make up the stocks {73}
+necessary for such a special study. In the case of green we might perhaps
+have employed a similar method, performing all experiments with a common
+difference from the gray in all flies used.
+
+CHROME.
+
+In a stock of forked fused there appeared, September 15, 1913, three males
+of a brownish-yellow body-color. They were uniform in color, without any of
+the abdominal banding so striking in other body-colors. Even the tip of the
+abdomen lacked the heavy pigmentation which is a marked secondary sexual
+character of the male. About 20 or more of these males appeared in the same
+culture. This appearance of many males showing a mutant character and the
+non-appearance of corresponding females is usual for sex-linked characters.
+In such cases females appear in the next generation, as they did in this
+case when the chrome males were mated to their sisters in mass cultures.
+Since both females and males of chrome were on hand, it should have been an
+easy matter to continue the stock, but many matings failed, and it was
+necessary to resort to breeding in heterozygous form. The chrome, however,
+gradually disappeared from the stock. Such a difficult sex-linked mutation
+as this could be successfully handled (like a lethal) if it could be mated
+to a double recessive whose members lie one on each side of the mutant, but
+in the case of chrome this was not attempted soon enough to save the stock.
+
+LETHAL 3.
+
+In the repetition of a cross between a white miniature male and a vermilion
+pink male (December 1913), the F_2 ratios among the males were seen to be
+very much distorted because of the partial absence of certain classes
+(Morgan 1914_c_). While it was suspected that the disturbance was due to a
+lethal, the data were useless for determining the position of such a
+lethal, from the fact that more than one mother had been used in each
+culture. From an F_2 culture that gave practically a 2:1 sex-ratio,
+vermilion females were bred to club males. Several such females gave
+sex-ratios. Their daughters were again mated to vermilion males. Half of
+these daughters gave high female sex-ratios and showed the linkage
+relations given in table 55.
+
+TABLE 55.--_Linkage data on club, lethal 3, and vermilion, from Morgan,
+1914c_.
+
+  +----------+-----------------------------------------------------------+
+  |          |                             Males.                        |
+  |          +-----------+--------------+------------------+-------------+
+  |          |  c_1      |  c_1 l_3 v   |  c_1  v          |  c_1 l_3    |
+  | Females. |  -------  |  --+------   |  ----+-          |  --+--+--   |
+  |          |    l_3 v  |              |    l_3           |         v   |
+  |          +-----------+--------------+------------------+-------------+
+  |          |  Club.    |  Wild-type.  |  Club vermilion. |  Vermilion. |
+  +----------+-----------+--------------+------------------+-------------+
+  |  588     |   182     |    28        |    11            |    1        |
+  +----------+-----------+--------------+------------------+-------------+
+
+{74}
+
+Lethal 3 proved to lie between club and vermilion, 13 units from club and 5
+from vermilion. The same locus was indicated by the data from the cross of
+vermilion lethal-bearing females by eosin miniature males. The complete
+data bearing on the position of lethal 3 is summarized in table 56. On the
+basis of this data lethal 3 is located at 26.5.
+
+TABLE 56.--_Summary of linkage data on lethal 3, from Morgan, 1914c_.
+
+  +---------------------+--------+--------+------------+
+  |     Gens.           | Total. | Cross- | Cross-over |
+  |                     |        | overs. | values.    |
+  +---------------------+--------+--------+------------+
+  | Eosin lethal 3      | 1,327  |  268   |    20.2    |
+  | Eosin vermilion     | 1,327  |  357   |    27.0    |
+  | Eosin miniature     | 3,374  |  967   |    29.0    |
+  | Club lethal 3       |   222  |   29   |    13.0    |
+  | Club vermilion      |   877  |  161   |    18.4    |
+  | Lethal 3 vermilion  | 1,549  |  105   |     6.8    |
+  | Lethal 3 miniature  | 1,481  |  138   |     9.3    |
+  | Vermilion miniature | 1,327  |   31   |     2.3    |
+  +---------------------+--------+--------+------------+
+
+LETHAL 3a.
+
+In January 1914 a vermilion female from a lethal 3 culture when bred to a
+vermilion male gave 71 daughters and only 3 sons; 34 of these daughters
+were tested, and every one of them gave a 2:1 sex-ratio. The explanation
+advanced (Morgan 1914_c_) was that the mother of the high ratio was
+heterozygous for lethal 3, and also for another lethal that had arisen by
+mutation in the X chromosome brought in by the sperm. On this
+interpretation the few males that survived were those that had arisen
+through crossing-over. The rarity of the sons shows that the two lethals
+were in loci near together, although here of course in different
+chromosomes, except when one of them crossed over to the other. As
+explained in the section on lethal 1 and 1_a_ the distance between the two
+lethals can be found by taking twice the number of the surviving males
+(2+3) as the cross-overs and the number of the females as the
+non-cross-overs. But the 34 daughters tested were also non-cross-overs,
+since none of them failed to carry a lethal. The fractions (6+0)/(71+34) =
+6/105 give 5.7 as the distance between the lethals in question. In the case
+of lethals 3 and 3_a_ another test was applied which showed graphically
+that two lethals were present. Each of the daughters tested showed, by the
+classes of her sons, the amount of crossing-over between white and that
+lethal of the two that she carried. These cross-over values were plotted
+and gave a bimodal curve with modes 7 units apart. It had already been
+shown that the locus of one of the two lethals was at 26.5, and since the
+higher of the two modes was at about 23, it corresponds to lethal 3. The
+data and the curve show that the lethals 3 and 3_a_ are about 7 units
+apart, _i. e._, lethal 3_a_ lies at about 19.5. {75}
+
+LETHAL 1b.
+
+A cross between yellow white males and abnormal abdomen females gave
+(February 1914) regular results in 10 F_2 cultures, but three cultures gave
+2 [female] : 1 [male] sex-ratios (Morgan, 1914_b_, p. 92). The yellow white
+class, which was a non-cross-over class in these 10 cultures, had
+disappeared in the 3 cultures. Subsequent work gave the data summarized in
+table 57. At the time when the results of table 57 were obtained it did not
+seem possible that two different lethals could be present in the space of
+about 1 unit between yellow and white, and this lethal was thought to be a
+reappearance of lethal 1 (Morgan, 1912_b_, p. 92). Since then a large
+number of lethals have arisen, one of them less than 0.1 unit from yellow,
+and at least one other mutation has taken place between yellow and white,
+so that the supposition is now rather that the lethal in question was not
+lethal 1. Indeed, the linkage data show that this lethal, which may be
+called lethal 1_b_, lies extraordinarily close to white, for the distance
+from yellow was 0.8 unit and of white from yellow on the basis of the same
+data 0.8. There was also a total absence of cross-overs between lethal 1_b_
+and white in the total of 846 flies which could have shown such
+crossing-over. On the basis of this linkage data alone we should be obliged
+to locate lethal 1_b_ at the point at which white itself is situated,
+namely, 1.1, but on _a priori_ grounds it seems improbable that a lethal
+mutation has occurred at the same locus as the factor for white eye-color.
+Farther evidence against this supposition is that females that have one X
+chromosome with both yellow and white and the other X chromosome with
+yellow, lethal, and white are exactly like regular stock yellow white
+flies. The lethal must have appeared in a chromosome which was already
+carrying white and yet did not affect the character of the white. We
+prefer, therefore, to locate lethal 1_b_ at 1.1-.
+
+TABLE 57.--_Summary of all linkage data upon lethal 1b, from Morgan,
+1914b_.
+
+  +-------------------------+---------+--------+---------------+
+  |     Gens.               |  Total. | Cross- | Cross-over    |
+  |                         |         | overs. | values.       |
+  +-------------------------+---------+--------+---------------+
+  | Yellow lethal 1_b_      |   744   |   6    |  0.81         |
+  | Yellow white            | 2,787   |  23    |  0.82         |
+  | Lethal 1_b_ white       |   846   |   0    |  0.0          |
+  +-------------------------+---------+--------+---------------+
+
+FACET.
+
+Several autosomal mutations had been found in which the facets of the
+compound eye are disarranged. One that was sex-linked appeared in February
+1914. Under the low power of the binocular microscope the facets are seen
+to be irregular in arrangement, instead of being arranged in a strictly
+regular pattern. The ommatidia are more nearly circular than hexagonal in
+outline, and are variable in size, some being considerably larger than
+normal. The large ones are also darker than {76} the smaller, giving a
+blotched appearance to the eye. The short hairs between the facets point in
+all directions instead of radially, as in the normal eye. The irregular
+reflection breaks up the dark fleck which is characteristic of the normal
+eye. The shape of the eye differs somewhat from the normal; it is more
+convex, smaller, and is encircled by a narrow rim destitute of ommatidia.
+
+Facet arose in a back-cross to test the independence of speck (second
+chromosome) and maroon (third chromosome). One of the cultures produced,
+among the first males to hatch, some males which showed the facet
+disarrangement. None of the females showed this character. The complete
+output was that typical of a female heterozygous for a recessive sex-linked
+character: not-facet [female] [female] (2), 112; not-facet [male] [male]
+(1), 57; facet [male] [male] (1), 51.
+
+Of the three characters which were shown by the F_2 males, one, facet, is
+sex-linked, another, speck, is in the second chromosome, and maroon is in
+the third chromosome. All eight F_2 classes are therefore expected to be
+equal in size, and each pair of characters should show free assortment,
+that is, 50 per cent. The assortment value for facet speck is 48, for speck
+maroon 52, and for facet maroon 48, as calculated from the F_2 males of
+table 58.
+
+TABLE 58.--_P_1 speck maroon_ [male] x _wild_ [female] [female]. _B.C. F_1
+wild-type_ [female] x _speck maroon_ [male].
+
+  +----------+----------------------------+
+  |          |        F_2 females.        |
+  |Reference.+-------+-----+------+-------+
+  |          |Speck  |Wild-|Speck.|Maroon.|
+  |          |maroon.|type.|      |       ~
+  |          |       |     |      |       ~
+  +----------+-------+-----+------+-------+
+  |     66   |  31   |  30 |   26 |   25  |
+  +----------+-------+-----+------+-------+
+
+  +----------------------------------------------------------+
+  |                          F_2 males.                      |
+  +------+-------+-------+-----+-------+------+------+-------+
+  |Facet.|Speck  |Facet  |Wild-|Facet  |Speck.|Facet |Maroon.|
+  ~      |maroon.|speck  |type.|maroon.|      |speck.|       |
+  ~      |       |maroon.|     |       |      |      |       |
+  +------+-------+-------+-----+-------+------+------+-------+
+  |  14  |  14   |  14   |  10 |   11  |   17 |  12  |  17   |
+  +------+-------+-------+-----+-------+------+------+-------+
+
+LINKAGE OF FACET, VERMILION AND SABLE.
+
+In order to determine the location of facet in the first chromosome, one of
+the facet males which appeared in culture 66 was crossed out to vermilion
+sable females. Three of the wild-type daughters were back-crossed to
+vermilion sable males. The females of the next generation should give data
+upon the linkage of vermilion and sable, while the males should show the
+linkage of all three gens, facet, vermilion, and sable. The offspring of
+these three females are classified in table 59.
+
+The cross-over fraction for vermilion sable as calculated from the females
+is 19/194. The cross-over value corresponding to this fraction is 10 units,
+which was the value found in the more extensive experiments given in the
+section on sable.
+
+It will be noticed that the results in the males of culture 150 are
+markedly different from those of the other two pairs. While the sable males
+are fully represented, their opposite classes, the gray males, are {77}
+entirely absent. This result is due to a lethal factor, lethal 5, which
+appeared in this culture for the first time.
+
+The males of the two cultures 149 and 151 give the order of gens as facet,
+vermilion, sable; that is, facet lies to the left of vermilion and toward
+yellow. The cross-over values are: facet vermilion 40; vermilion sable 12;
+facet sable 42. Since yellow and vermilion usually give but 34 per cent of
+crossing-over, this large value of 40 for facet vermilion shows that facet
+must lie very near to yellow.
+
+TABLE 59.--_P_1 facet_ [male] x _vermilion sable_ [female] [female]. _B.C.
+F_1 wild-type_ [female] x _vermilion sable_ [male] [male].
+
+  +----------+----------------------------------+
+  |          |           F_2 females.           |
+  |          +----------------+-----------------+
+  |          |                |                 |
+  |          |Non-cross-overs.|   Cross-overs.  |
+  |          |                |                 |
+  |Reference.+---------+------+----------+------+
+  |          |Vermilion|Wild- |Vermilion.|Sable.|
+  |          |sable.   |type. |          |      ~
+  |          |         |      |          |      ~
+  +----------+---------+------+----------+------+
+  | 149      |  16     |  29  |    3     |  3   |
+  | 150      |  13     |  17  |    2     |  2   |
+  | 151      |  37     |  63  |    7     |  2   |
+  |          +---------+------+----------+------+
+  |   Total. |  66     | 109  |   12     |  8   |
+  +----------+---------+------+----------+------+
+
+  +--------------------------------------------------------------------+
+  |                         F_2 males.                                 |
+  +----------------+---------------+-----------------+-----------------+
+  |   f_a          |   f_a v s     |     f_a  s      |      f_a v      |
+  |   ------       |   --+----     |     ----+-      |      --+--+--   |
+  |      v s       |               |        v        |            s    |
+  +------+---------+---------+-----+------+----------+----------+------+
+  |Facet.|Vermilion|Facet    |Wild-|Facet |Vermilion.|Facet     |Sable.|
+  ~      |sable.   |vermilion|type.|sable.|          |vermilion.|      |
+  ~      |         |sable.   |     |      |          |          |      |
+  +------+---------+---------+-----+------+----------+----------+------+
+  | 17   | 10      |  8      | 12  |  2   |  ..      |  2       |  1   |
+  | ..   | 10      |  9      | ..  |  1   |  ..      | ..       | ..   |
+  | 38   | 23      | 12      | 26  |  2   |   8      |  4       |  1   |
+  +------+---------+---------+-----+------+----------+----------+------+
+  | 55   | 43      | 29      | 38  |  5   |   8      |  6       |  2   |
+  +------+---------+---------+-----+------+----------+----------+------+
+
+LINKAGE OF EOSIN, FACET, AND VERMILION.
+
+In order to obtain more accurate information on the location of facet, a
+facet male was mated to an eosin vermilion female. The F_1 females were
+mated singly to wild males and they gave the results shown in table 60. The
+F_2 females were not counted, since they do not furnish any information.
+The evidence of table 60 places facet at 1.1 units to the right of eosin,
+or at 2.2.
+
+TABLE 60.--_P_1 eosin vermilion_ [female] x _facet_ [male]. _F_1 wild-type_
+[female] x _wild_ [male].
+
+  +----------+-----------------+-----------------+-----------------+
+  |          |     w^c   v     |   w^c f_a       |     w^c         |
+  |          |     -------     |   --+----       |     ----+-      |
+  |          |       f_a       |         v       |      f_a v      |
+  |Reference.+----------+------+------+----------+------+----------+
+  |          |Eosin     |Facet.|Eosin |Vermilion.|Eosin.|Facet     |
+  |          |vermilion.|      |facet.|          |      |vermilion.|
+  |          |          |      |      |          |      |          |
+  +----------+----------+------+------+----------+------+----------+
+  | 512      |  43      |  43  | ..   |   1      |  13  |  16      ~
+  | 513      |  28      |  35  | ..   |   2      |  19  |   5      ~
+  | 514      |  18      |  31  |  1   |  ..      |  17  |  11      |
+  | 515      |  18      |  60  | ..   |  ..      |  20  |  15      |
+  | 516      |  10      |  31  | ..   |  ..      |   7  |  12      |
+  | 517      |  24      |  34  | ..   |  ..      |  10  |  12      |
+  | 518      |  44      |  38  |  1   |   1      |  23  |  22      |
+  +----------+----------+------+------+----------+------+----------+
+  |    Total.| 185      | 272  |  2   |   4      | 109  |  93      |
+  +----------+----------+------+------+----------+------+----------+
+
+  +----------------+------+----------------------------+
+  |   w^c f_a v    |      |                            |
+  |   --+---+--    |      |     Cross-over values.     |
+  |                |      |                            |
+  +----------+-----+Total.+------+----------+----------+
+  |Eosin     |Wild-|      |Eosin |Facet     |Eosin     |
+  |facet     |type.|      |facet.|vermilion.|vermilion.|
+  |vermilion.|     |      |      |          |          |
+  +----------+-----+------+------+----------+----------+
+  ~  ..      | ..  | 116  | .... | ....     | ....     |
+  ~  ..      | ..  |  89  | .... | ....     | ....     |
+  |  ..      | ..  |  78  | .... | ....     | ....     |
+  |  ..      | ..  | 113  | .... | ....     | ....     |
+  |  ..      | ..  |  60  | .... | ....     | ....     |
+  |  ..      | ..  |  80  | .... | ....     | ....     |
+  |  ..      |  1  | 130  | .... | ....     | ....     |
+  +----------+-----+------+------+----------+----------+
+  |  ..      |  1  | 666  | 1.05 | 30.5     | 31.3     |
+  +----------+-----+------+------+----------+----------+
+
+{78}
+
+LETHAL SC.
+
+The third of the lethals which Miss Stark found (Stark, 1915) while she was
+testing the relative frequency of occurrence of lethals in fresh and inbred
+wild stocks arose in April 1914 in stock caught in 1910. Females
+heterozygous for this lethal, lethal _sc_, were mated to white males and
+the daughters were back-crossed to white males. Half of the daughters gave
+lethal sex-ratio, and these gave 1,405 cross-overs in a total of 3,053
+males, from which the amount of crossing-over between white and lethal _sc_
+has been calculated as 46 per cent.
+
+By reference to table 65 it is seen that white and bar normally give only
+about 44 per cent of crossing-over in a two-locus experiment; lethal _sc_
+then is expected to be situated at least as far to the right as bar.
+Females heterozygous for lethal _sc_ were therefore crossed to bar males,
+and their daughters were tested. The lethal-bearing daughters gave 144
+cross-overs in a total of 1,734 males, that is, bar and lethal _sc_ gave
+8.3 per cent of crossing-over. Lethal _sc_ therefore lies 8.3 units beyond
+bar or at about 66.5. The cross-over value sable lethal _sc_ was found to
+be 23.5 (387 cross-overs in a total of 1,641 males) which places the lethal
+at 43+23.5, or at 66.5. We know from other data that there is enough double
+crossing-over in the distance which gives an experimental value of 23.5 per
+cent, so that the true distance is a half unit longer or the locus at 67.0
+is indicated by the 1,641 males of the sable lethal experiment. In a
+distance so short that the experimental value is only 8.3 per cent there
+is, as far as we have been able to determine, no double crossing-over at
+all, or at most an amount that is entirely negligible, so that a locus at
+57+8.3 or 65.3 is indicated by the 1,734 males of the bar lethal
+experiment. To get the value indicated by the total data the cases may be
+weighted, that is, the value 65.3 may be multiplied by 1,734, and 67.0 may
+be multiplied by 1,641. The sum of these two numbers divided by the sum of
+1,734 and 1,641 gives 66.2 as the locus indicated by all the data
+available. This method has been used in every case where more than one
+experiment furnishes data upon the location of a factor. In constructing
+the map given in diagram I rather complex balancings were necessary.
+
+LETHAL SD.
+
+The fourth lethal which Miss Stark found (May 1914) in the inbred stocks of
+_Drosophila_ has not been located by means of linkage experiments. It is
+interesting in that the males which receive the lethal factor sometimes
+live long enough to hatch. These males are extremely feeble and never live
+more than two days. There is, as far as can be seen, no anatomical defect
+to which their extreme feebleness and early death can be attributed. {79}
+
+FURROWED.
+
+In studying the effect of hybridization upon the production of mutations in
+_Drosophila_, F. N. Duncan found a sex-linked mutation which he called
+"furrowed eye" (Duncan 1915). The furrowed flies are characterized by a
+foreshortening of the head, which causes the surface of the eye to be
+thrown into irregular folds with furrows between. The spines of the
+scutellum are stumpy, a character which is of importance in classification,
+since quite often flies occur which have no noticeable disturbance of the
+eyes.
+
+The locus of furrowed was determined to be at 38.0 on the basis of the data
+given in table 61.
+
+TABLE 61.--_Data on the linkage of furrowed, from Duncan, 1915_.
+
+  +------------+-------------------------------------------+------+
+  |   Gens.    |               F_2 males.                  |      |
+  +------------+---------+---------+-----------+-----------+      +
+  |            | w^e m   | w^e f_w | w^e m f_w | w^e       |Total.|
+  |            | ------- | --+---- | -----+--- | --+--+--  |      |
+  |            |     f_w |     m   |           |     m f_w |      |
+  |            +---------+---------+-----------+-----------+------+
+  |Eosin,      |         |         |           |           |      |
+  |  miniature,|         |         |           |           |      |
+  |  furrowed  |   142   |    59   |     4     |    3      | 208  |
+  |            +=========+=========+===========+===========+======+
+  |            | f_w     | f_w s f | f_w  f    | f_w s     |      |
+  |            | ------- | --+---- | ----+-    | --+--+--  |      |
+  |            |    s  f |         |   s       |        f  |      |
+  |            |---------+---------+-----------+-----------+------+
+  |Furrowed,   |         |         |           |           |      ~
+  |  sable,    |         |         |           |           |      ~
+  |  forked    |   166   |     9   |    31     |    3      | 209  |
+  |            +=========+=========+===========+===========+======+
+  |            | v    B' | v f_w   | v         | v f_w B'  |      |
+  |            | ------- | -+----- | ----+--   | -+---+--  |      |
+  |            |  f_w    |      B' |  f_w B'   |           |      |
+  |            +---------+---------+-----------+-----------+------+
+  |Vermilion,  |         |         |           |           |      |
+  |  furrowed, |         |         |           |           |      |
+  |  bar       |   188   |     9   |    43     |    0      | 240  |
+  +------------+---------+---------+-----------+-----------+------+
+
+  +------------------------------+
+  |      Cross-over values.      |
+  +----------+---------+---------+
+  |Eosin     |Miniature|Eosin    |
+  |miniature.|furrowed.|furrowed.|
+  |          |         |         |
+  +----------+---------+---------+
+  |          |         |         |
+  |          |         |         |
+  | 29.8     |  30.4   |  30.3   |
+  +==========+=========+=========+
+  |Furrowed  |Sable    |Furrowed |
+  |sable.    |forked.  |forked.  |
+  |          |         |         |
+  +----------+---------+---------+
+  ~          |         |         |
+  ~          |         |         |
+  |  5.7     |  16.3   |  19.1   |
+  +==========+=========+=========+
+  |Vermilion |Furrowed |Vermilion|
+  |furrowed. |bar.     |bar.     |
+  |          |         |         |
+  +----------+---------+---------+
+  |          |         |         |
+  |          |         |         |
+  |  3.8     |  21.6   |  17.9   |
+  +----------+---------+---------+
+
+ADDITIONAL DATA FOR YELLOW, WHITE, VERMILION, AND MINIATURE.
+
+Considerable new work has been done by various students upon the linkage of
+the older mutant characters, namely, yellow, white, vermilion, and
+miniature. We have summarized these new data, and they give values very
+close to those already published. We have included in the white miniature
+data those published by P. W. Whiting (Whiting 1913). {80}
+
+TABLE 62.--_Data upon the linkage of yellow, white, vermilion, and
+miniature_ (_contributed by students_).
+
+  +--------------------+-----------------+-------------+-------+----------+
+  | Gens.              | Non-cross-overs.| Cross-overs.|       |          |
+  +--------------------+-----------------+-------------+       |          |
+  |                    | w           m   | w           |Total. |Cross-over|
+  |                    | -------------   | -----+----- |       |values.   |
+  |                    |                 |           m |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |White miniature.    | 6,219[8] 7,378  | 3,754 3,337 |20,688 |   34.2   |
+  |                    +=================+=============+=======+==========+
+  |                    | w               | w         m |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |             m   |             |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |                    | 1,651   1,116   |   671 1,047 | 4,485 |   38.3   |
+  |                    +=================+=============+=======+==========+
+  |                    | y               | y         m |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |             m   |             |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |Yellow miniature.   |   761     923   |   421   653 | 2,758 |   39     |
+  |                    +=================+=============+=======+==========+
+  |                    | v               | v         m |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |             m   |             |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |Vermilion miniature.| 1,685   1,460   |    32    36 | 3,213 |    2.1   |
+  |                    +=================+=============+=======+==========+
+  |                    | y           w   | y           |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |                 |           w |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |Yellow white.       | 1,600   1,807   |    10     7 | 3,424 |    0.5   |
+  |                    +=================+=============+=======+==========+
+  |                    | y           v   | y           |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |                 |           v |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |Yellow vermilion.   |   509     587   |   328   284 | 1,708 |   35.8   |
+  |                    +=================+=============+=======+==========+
+  |                    | w          B'   | w           |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |                 |          B' |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |White bar.          |   198     272   |   168   166 |   804 |   42     |
+  |                    +=================+=============+=======+==========+
+  |                    | b_1             | b_1       r |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |             r   |             |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |Bifid rudimentary.  |   142      15   |    12   116 |   285 |   45     |
+  |                    +=================+=============+=======+==========+
+  |                    | r               | r         f |       |          |
+  |                    | -------------   | -----+----- |       |          |
+  |                    |             f   |             |       |          |
+  |                    +-----------------+-------------+-------+----------+
+  |Rudimentary forked. |    73     211   |   ...     4 |   288 |    1.4   |
+  +--------------------+-----------------+-------------+-------+----------+
+
+{81}
+
+NEW DATA CONTRIBUTED BY A. H. STURTEVANT AND H. J. MULLER.
+
+Data from several experiments upon sex-linked characters described in this
+paper have been contributed by Dr. A. H. Sturtevant and Mr. H. J. Muller,
+and are given in table 63.
+
+TABLE 63.--_Data contributed by A. H. Sturtevant and H. J. Muller._
+
+  +---------------------+-----------------------------------+------+
+  |Gens.                |              Classes.             |      |
+  +---------------------+--------+--------+--------+--------+      |
+  |                     | y w    | y   b_1| y w b_1| y      |Total.|
+  |                     | -------| -+-----| ---+---| -+--+--|      |
+  |                     |     b_1|  w     |        |  w b_1 |      |
+  |                     +--------+--------+--------+--------+------+
+  |Yellow white x bifid.| 233 254|  1   2 | 10   6 | ..  .. |  506 |
+  |                     +========+========+========+========+======+
+  |                     | y      | y v B' | y    B'| y v    |      |
+  |                     | -------| -+-----| ---+---| -+--+--|      |
+  |                     |    v B'|        |    v   |      B'|      |
+  |Yellow x vermilion   +--------+--------+--------+--------+------+
+  |bar.                 | 99 101 | 60  55 | 49  48 |  9  14 |  435 |
+  |                     +========+========+========+========+======+
+  |                     | w b_1  | w     f| w b_1 f| w      |      |
+  |                     | -------| -+-----| ---+---| -+--+--|      |
+  |                     |       f|    b   |        |   b_1 f|      |
+  |                     +--------+--------+--------+--------+------+
+  |White bifid x forked.| 84  77 |  9   6 | 65  59 |  1   5 |  306 |
+  |                     +========+========+========+========+======+
+  |                     | v m    | v     s| v m   s| v      |      |
+  |                     | -------| -+-----| ---+---| -+--+--|      |
+  |                     |       s|    m   |        |    m  s|      |
+  |Vermilion miniature  +--------+--------+--------+--------+------+
+  |x sable.             | 152 111|  4   2 |  5  12 |  ..  ..|  286 |
+  |                     +========+========+========+========+======+
+  |                     | s    r | s     f| s  r  f| s      |      ~
+  |                     | -------| -+-----| ----+--| -+--+--|      ~
+  |                     |       f|      r |        |    r  f|      |
+  |Sable rudimentary x  +--------+--------+--------+--------+------+
+  |forked.              | 143 195| 26  27 |  4   3 |  ..  ..|  398 |
+  +---------------------+--------+--------+--------+--------+------+
+  |                  WHITE BIFID x RUDIMENTARY.                    |
+  +---------------------+-----------------------------------+------+
+  |  F_{2} females.     |            F_{2} males.           |      |
+  +--------+------------+--------+--------+--------+--------+      |
+  |w   b_1 | w          | w b_1  | w   r  | w b_1 r| w      |Total.|
+  |------- | --+---     | -------| -+---  | -----+-| +---+- |      |
+  |        |    b_1     |      r |   b_1  |        |  b_1 r |      |
+  +--------+------------+--------+--------+--------+--------+------+
+  |228 335 | 15  11     | 150 66 |  2  10 | 29  135|  2   1 |  395 |
+  +--------+------------+--------+--------+--------+--------+------+
+  |             WHITE BIFID x MINIATURE RUDIMENTARY.               |
+  +--------+------------+--------+--------+--------+--------+------+
+  |w   b_1 | w          |        |        |        |        |      |
+  |------- | --+---     | ------ |  -+--- | ---+---| -----+-|-+-+--|
+  |        |    b_1     |        |        |        |        |      |
+  +--------+------------+--------+--------+--------+--------+------+
+  |  344   |   31       |  109   |     2  |    58  |    41  |   2  |
+  +--------+------------+--------+--------+--------+--------+------+
+
+  +--------------------------------------+
+  |          Cross-over values.          |
+  +------------+------------+------------+
+  | Yellow     |  White     | Yellow     |
+  |  white.    |  bifid.    | bifid.     |
+  |            |            |            |
+  +------------+------------+------------+
+  |   0.6      |   3.2      |   3.8      |
+  +============+============+============+
+  | Yellow     |Vermilion   | Yellow     |
+  |vermilion.  |   bar.     |   bar.     |
+  |            |            |            |
+  +------------+------------+------------+
+  |   32       |  28        |  49        |
+  +============+============+============+
+  |  White     |  Bifid     |  White     |
+  |  bifid.    | forked.    | forked.    |
+  |            |            |            |
+  +------------+------------+------------+
+  |    7       |  42        |  45        |
+  +============+============+============+
+  | Vermilion  |Miniature   |Vermilion   |
+  | miniature. |  sable.    |  sable.    |
+  |            |            |            |
+  +------------+------------+------------+
+  |    2.1     |   6        |   8.1      |
+  +============+============+============+
+  ~  Sable     |Rudimentary |  Sable     |
+  ~rudimentary.|  forked.   | forked.    |
+  |            |            |            |
+  +------------+------------+------------+
+  |    13.3    |   1.8      |  15        |
+  +------------+------------+------------+
+  |      WHITE BIFID x RUDIMENTARY.      |
+  +--------------------------------------+
+  |           Cross-over values.         |
+  +------------+------------+------------+
+  |   White    |  Bifid     |   White    |
+  |   bifid.   |rudimentary.|rudimentary.|
+  |            |            |            |
+  +------------+------------+------------+
+  |     3.8    |  42.3      |  44.5      |
+  +------------+------------+------------+
+  | WHITE BIFID x MINIATURE RUDIMENTARY. |
+  +------------+------------+------------+
+  |            |            |            |
+  |  -+--+-    |  ---+-+-   | -+-+-+-    |
+  |            |            |            |
+  +------------+------------+------------+
+  |     0      |      6     |    1       |
+  +------------+------------+------------+
+
+{82}
+
+SUMMARY OF THE PREVIOUSLY DETERMINED CROSS-OVER VALUES.
+
+The data of the earlier papers, namely, Dexter, 1912; Morgan, 1910_c_,
+1911_a_, 1911_f_, 1912_f_, 1912_g_; Morgan and Bridges, 1913; Morgan and
+Cattell, 1912 and 1913; Safir, 1913; Sturtevant, 1913 and 1915; and Tice,
+1914, have been summarized in a recent paper by Sturtevant (Sturtevant,
+1915) and are given here in table 64. Our summary combines three summaries
+of Sturtevant, viz, that of single crossing-over and two of double
+crossing-over.
+
+TABLE 64.--_Previously published data summarized from Sturtevant, 1915_.
+
+  +------------------------+--------+-------------+------------+
+  |     Factors.           | Total. | Cross-overs.| Cross-over |
+  |                        |        |             | values.    |
+  +------------------------+--------+-------------+------------+
+  | Yellow white.          | 46,564 |    498      |    1.07    |
+  | Yellow vermilion.      | 10,603 |  3,644      |   33.4     |
+  | Yellow miniature.      | 18,797 |  6,440      |   34.3     |
+  | Yellow rudimentary.    |  2,563 |  1,100      |   42.9     |
+  | Yellow bar.            |    191 |     88      |   46.1     |
+  | White vermilion.       | 15,257 |  4,910      |   32.1     |
+  | White miniature.       | 41,034 | 13,513      |   32.8     |
+  | White rudimentary.     |  5,847 |  2,461      |   42.1     |
+  | White bar.             |  5,151 |  2,267      |   44.0     |
+  | Vermilion miniature.   |  5,329 |    212      |    4.0     |
+  | Vermilion rudimentary. |  1,554 |    376      |   24.1     |
+  | Vermilion bar.         |  7,514 |  1,895      |   25.2     |
+  | Miniature rudimentary. | 12,567 |  2,236      |   17.8     |
+  | Miniature bar.         |  3,112 |    636      |   20.4     |
+  | Rudimentary bar.       |    159 |      7      |    4.4     |
+  +------------------------+--------+-------------+------------+
+
+{83}
+
+SUMMARY OF ALL DATA UPON LINKAGE OF GENS IN CHROMOSOME I.
+
+In table 65 all data so far secured upon the sex-linked characters are
+summarized. These data include the experiments previously published in the
+papers given in the bibliography and the experiments given here. The data
+from experiments involving three or more loci are calculated separately for
+each value and included in the totals.
+
+TABLE 65.--_A summary of all linkage data upon chromosome I_.
+
+  +----------------------------+----------+--------------+------------+
+  |     Gens.                  |  Total.  | Cross-overs. | Cross-over |
+  |                            |          |              | values.    |
+  +----------------------------+----------+--------------+------------+
+  | Yellow lethal 1.           |     131  |      1       |  0.8       |
+  | Yellow lethal 1_b_.        |     744  |      6       |  0.8       |
+  | Yellow white.              |  81,299  |    875       |  1.1       |
+  | Yellow abnormal.           |  15,314  |    299       |  2.0       |
+  | Yellow bifid.              |   3,681  |    201       |  5.5       |
+  | Yellow club.               |     525  |     93       | 17.7       |
+  | Yellow vermilion.          |  13,271  |  4,581       | 34.5       |
+  | Yellow miniature.          |  21,686  |  7,559       | 34.3       |
+  | Yellow sable.              |   1,600  |    686       | 42.9       |
+  | Yellow rudimentary.        |   2,563  |  1,100       | 42.9       |
+  | Yellow bar.                |     626  |    300       | 47.9       |
+  | Lethal 1 white.            |   1,763  |      7       |  0.4       |
+  | Lethal 1 miniature.        |     814  |    323       | 39.7       |
+  | Lethal 1_b_ white.         |     846  |      0       |  0.0       |
+  | White facet.               |     666  |      7       |  1.1       |
+  | White abnormal.            |  16,300  |    277       |  1.7       |
+  | White bifid.               |  23,595  |  1,260       |  5.3       |
+  | White lethal 2.            |   8,011  |    767       |  9.6       |
+  | White club.                |   2,251  |    321       | 14.3       |
+  | White lethal _sb_.         |   3,678  |    572       | 15.6       |
+  | White lemon.               |     241  |     35       | 14.5       |
+  | White depressed.           |      59  |     12       | 20.3       |
+  | White lethal _sa_.         |   1,150  |    256       | 22.2       |
+  | White vermilion.           |  27,962  |  8,532       | 30.5       |
+  | White reduplicated.        |     418  |    121       | 28.9       |
+  | White miniature.           | 110,701  | 31,071       | 33.2       |
+  | White furrowed.            |     208  |     63       | 30.3       |
+  | White sable.               |   2,511  |  1,032       | 41.2       |
+  | White rudimentary.         |   6,461  |  2,739       | 42.4       |
+  | White forked.              |   3,664  |  1,676       | 45.7       |
+  | White bar.                 |   5,955  |  2,601       | 43.6       |
+  | White fused.               |     430  |    186       | 43.3       |
+  | White lethal _sc_.         |   3,053  |  1,406       | 46.0       |
+  | Facet vermilion.           |     852  |    278       | 32.6       |
+  | Facet sable.               |     186  |     80       | 43.0       |
+  | Bifid vermilion.           |   2,724  |    849       | 31.1       |
+  | Bifid miniature.           |     219  |     67       | 30.6       |
+  | Bifid rudimentary.         |     899  |    384       | 42.7       |
+  | Bifid forked.              |     306  |    130       | 42.5       |
+  | Lethal 2 vermilion.        |   1,400  |    248       | 17.7       |
+  | Lethal 2 miniature.        |   6,752  |  1,054       | 15.4       |
+  | Club lethal 3.             |     222  |     29       | 13.0       |
+  | Club vermilion.            |   5,558  |  1,047       | 18.8       |
+  | Lethal _sb_ miniature.     |  3,678   |    733       | 19.9       |
+  | Lemon vermilion.           |     241  |     29       | 12.0       |
+  {84}
+  | Shifted vermilion.         |   1,007  |    155       | 15.5       |
+  | Shifted bar.               |     242  |     76       | 31.4       |
+  | Depressed vermilion.       |      59  |     10       | 17.0       |
+  | Depressed bar.             |     464  |    176       | 38.0       |
+  | Lethal 3 vermilion.        |   1,549  |    105       |  6.8       |
+  | Lethal 3 miniature.        |   1,481  |    138       |  9.3       |
+  | Vermilion dot.             |      57  |      0       |  0.0       |
+  | Vermilion reduplicated.    |     667  |     11       |  1.7       |
+  | Vermilion miniature.       |  10,155  |    317       |  3.1       |
+  | Vermilion furrowed.        |     240  |      9       |  3.8       |
+  | Vermilion sable.           |   9,209  |    929       | 10.1       |
+  | Vermilion rudimentary.     |   1,554  |    376       | 24.1       |
+  | Vermilion forked.          |     665  |    163       | 24.5       |
+  | Vermilion bar.             |  23,522  |  5,612       | 23.9       |
+  | Vermilion fused.           |   9,252  |  2,390       | 25.8       |
+  | Reduplicated bar.          |     583  |    120       | 20.6       |
+  | Miniature furrowed.        |     208  |      7       |  3.4       |
+  | Miniature sable.           |   1,855  |    125       |  6.7       |
+  | Miniature rudimentary.     |  12,786  |  2,284       | 17.9       |
+  | Miniature bar.             |   3,112  |    636       | 20.5       |
+  | Furrowed sable.            |     209  |     12       |  5.7       |
+  | Furrowed forked.           |     209  |     40       | 19.1       |
+  | Furrowed bar.              |     240  |     43       | 17.9       |
+  | Sable rudimentary.         |     663  |     95       | 14.3       |
+  | Sable forked.              |     872  |    140       | 16.0       |
+  | Sable bar.                 |   7,524  |  1,036       | 13.8       |
+  | Sable lethal _sc_.         |   1,641  |    387       | 23.6       |
+  | Rudimentary forked.        |   1,456  |     20       |  1.4       |
+  | Rudimentary bar.           |     664  |     15       |  2.3       |
+  | Forked bar.                |   1,706  |      8       |  0.5       |
+  | Forked fused.              |   1,201  |     37       |  3.1       |
+  | Bar fused.                 |   8,768  |    222       |  2.5       |
+  | Bar lethal _sc_.           |   1,734  |    144       |  8.3       |
+  +----------------------------+----------+--------------+------------+
+
+       *       *       *       *       *
+
+
+{85}
+
+BIBLIOGRAPHY.
+
+BRIDGES, CALVIN B.
+
+    1913. Non-disjunction of the sex-chromosomes of _Drosophila_. Jour.
+    Exp. Zool., 15, p. 587, Nov. 1913.
+
+    1914. Direct proof through non-disjunction that the sex-linked gens of
+    _Drosophila_ are borne by the X chromosome. Science, 40, p. 107, July
+    17, 1914.
+
+    1915. A linkage variation in _Drosophila_. Jour. Exp. Zool., 19, p. 1.
+    July 1915.
+
+    1916. Non-disjunction as proof of the chromosome theory of heredity.
+    First instalment, Genetics I, p. 1-52; second instalment, Genetics I,
+    No. 2, 107-164.
+
+CHAMBERS, R.
+
+    1914. Linkage of the factor for bifid wing. Biol. Bull. 27, p. 151,
+    Sept. 1914.
+
+DEXTER, JOHN S.
+
+    1912. On coupling of certain sex-linked characters in _Drosophila_.
+    Biol. Bull. 23, p. 183, Aug. 1912.
+
+    1914. The analysis of a case of continuous variation in _Drosophila_ by
+    a study of its linkage relations. Am. Nat., 48, p. 712, Dec. 1914.
+
+DUNCAN, F. N.
+
+    1915. An attempt to produce mutations through hybridization. Am. Nat.,
+    49, p. 575, Sept. 1915.
+
+HOGE, M. A.
+
+    1915. The influence of temperature on the development of a Mendelian
+    character. Jour. Exp. Zool., 18, p. 241.
+
+MORGAN, T. H.
+
+    1910a. Hybridization in a mutating period in _Drosophila_. Proc. Soc.
+    Exp. Biol. and Med., p. 160, May 18, 1910.
+
+    1910b. Sex-limited inheritance in _Drosophila_. Science 32, p. 120,
+    July 22, 1910.
+
+    1910c. The method of inheritance of two sex-limited characters in the
+    same animal. Proc. Soc. Exp. Biol. and Med., 8, p. 17.
+
+    1911a. An alteration of the sex-ratio induced by hybridization. Proc.
+    Soc. Exp. Biol. and Med., 8, No. 3.
+
+    1911b. The origin of nine wing mutations in _Drosophila_. Science, 33,
+    p. 496, Mar. 31, 1911.
+
+    1911c. The origin of five mutations in eye-color in _Drosophila_, and
+    their mode of inheritance. Science, April 7, 1911, 33, P. 534.
+
+    1911d. A dominant sex-limited character. Proc. Soc. Exp. Biol. and
+    Med., Oct. 1911.
+
+    1911e. Random segregation _versus_ coupling in Mendelian inheritance.
+    Science, 34, p. 384, Sept. 22, 1911.
+
+    1911_f_. An attempt to analyze the constitution of the chromosomes on
+    the basis of sex-linked inheritance in _Drosophila_. Jour. Exp. Zool.,
+    11, p. 365, Nov. 1911.
+
+    1912a. Eight factors that show sex-linked inheritance in _Drosophila_.
+    Science, Mar. 22, 1912.
+
+    1912c. Heredity of body-color in _Drosophila_. Jour. Exp. Zool., 13, p.
+    27, July 1912.
+
+    1912d. The masking of a Mendelian result by the influence of the
+    environment. Proc. Soc. Exp. Zool. and Med., 9, p. 73.
+
+    1912e. The explanation of a new sex-ratio in _Drosophila_. Science, 36,
+    p. 718, No. 22, 1912.
+
+    1912_f_. Further experiments with mutations in eye-color of
+    _Drosophila_. Jour. Acad. Nat. Sci. Phil., Nov. 1912.
+
+    1912_g_. A modification of the sex-ratio and of other ratios through
+    linkage. Z. f. ind. Abs. u. Veterb. 1912.
+
+    1914a. Another case of multiple allelomorphs in _Drosophila_. Biol.
+    Bull. 26, p. 231, Apr. 1914.
+
+    1914b. Two sex-linked lethal factors in _Drosophila_ and their
+    influence on the sex-ratio. Jour. Exp. Zool., 17, p. 81, July 1914.
+
+    1914c. A third sex-linked lethal factor in _Drosophila_. Jour. Exp.
+    Zool., 17, p. 315, Oct. 1914.
+
+    1914d. Sex-limited and sex-linked inheritance. Am. Nat., 48, P. 577,
+    Oct. 1914.
+
+    1915a. The infertility of rudimentary-winged females of _Drosophila_.
+    Am. Nat., 49, p. 40, Apr. 1915.
+
+    1915b. The role of the environment in the realization of a sex-linked
+    Mendelian character in _Drosophila_. Am. Nat., 49, p. 385, July 1915.
+
+{86}
+
+MORGAN, T. H., and C. B. BRIDGES.
+
+    1913. Dilution effects and bicolorism in certain eye-colors of
+    _Drosophila_. Jour. Exp. Zool., 15, p. 429, Nov. 1913.
+
+MORGAN, T. H., and ELETH CATTELL.
+
+    1912. Data for the study of sex-linked inheritance in _Drosophila_.
+    Jour. Exp. Zool., July, 1912.
+
+    1913. Additional data for the study of sex-linked inheritance in
+    _Drosophila_. Jour. Exp. Zool., Jan. 1913.
+
+MORGAN, T. H., and H. PLOUGH.
+
+    1915. The appearance of known mutations in other mutant stocks. Am.
+    Nat., 49, p. 318, May 1915.
+
+MORGAN, STURTEVANT, MULLER, and BRIDGES. The mechanism of Mendelian
+heredity. Henry Holt & Co., 1915.
+
+MORGAN, T. H., and S. C. TICE.
+
+    1914. The influence of the environment on the size of the expected
+    classes. Biol. Bull., 26, p. 213, Apr. 1914.
+
+RAWLS, ELIZABETH.
+
+    1913. Sex-ratios in _Drosophila ampelophila_. Biol. Bull. 24, p. 115,
+    Jan. 1913.
+
+SAFIR, S. R.
+
+    1913. A new eye-color mutation in _Drosophila_ and its mode of
+    inheritance. Biol. Bull. 25, p. 47, June 1913.
+
+STARK, M. B.
+
+    1915. The occurrence of lethal factors in inbred and wild stocks of
+    DROSOPHILA. Jour. Exp. Zool., 19, p. 531-538. Nov. 1915.
+
+STURTEVANT, A. H.
+
+    1913. The linear arrangement of six sex-linked factors in _Drosophila_
+    as shown by their mode of association. Jour. Exp. Zool., Jan. 1913.
+
+    1915. The behavior of the chromosomes as studied through linkage. Z. f.
+    Ind. Abs. u. Vereb. 1915.
+
+TICE, S. C.
+
+    1914. A new sex-linked character in _Drosophila_. Biol. Bull., Apr.,
+    1914.
+
+WHITING, P. W.
+
+    1913. Viability and coupling in _Drosophila_. Am. Nat., 47, p. 508,
+    Aug. 1913.
+
+       *       *       *       *       *
+
+
+DESCRIPTIONS OF PLATES.
+
+              PLATE I.
+
+  FIG. 1. Normal [female].
+
+  FIG. 2. Sable [female].
+
+  FIG. 3. Lemon [male].
+
+  FIG. 4. Abnormal abdomen [female].
+
+  FIG. 5. Abnormal abdomen [female].
+
+  FIG. 6. Yellow [female].
+
+              PLATE II.
+
+  FIG. 7. Eosin, miniature, black [male].
+
+  FIG. 8. Eosin, miniature, black [female].
+
+  FIG. 9. Cherry.
+
+  FIG. 10. Vermilion.
+
+  FIG. 11. White.
+
+  FIG. 12. Bar (from above).
+
+  FIG. 13. Bar (from side).
+
+  FIG. 14. Spot [female] (abdomen from above).
+
+  FIG. 15. Spot [female] (abdomen from side).
+
+  FIG. 16. Spot [male] (abdomen from above).
+
+  FIG. 17. Spot [male] (abdomen from side).
+
+[Illustration]
+
+[Illustration]
+
+       *       *       *       *       *
+
+
+Notes
+
+[1] For a fuller discussion see "The Mechanism of Mendelian Heredity" by
+Morgan, Sturtevant, Muller, and Bridges. Henry Holt & Co., 1915.
+
+[2] _B. C._ here and throughout stands for back-cross.
+
+[3] The first dark body-color mutation "black" (see plate II, figs. 7, 8)
+had appeared much earlier (Morgan 1911_b_, 1912_c_). It is an autosomal
+character, a member of the second group of linked gens. Still another dark
+mutant, "ebony," had also appeared, which was found to be a member of the
+third group of gens.
+
+[4] Wherever reference numbers are given, these denote the pages in the
+note-books of Bridges upon which the original entries for each culture are
+to be found.
+
+[5] In addition to these expected F_1 wild-type females there occurred 13
+females of an eye-color like that of the mutant pink. So far as was seen
+none of the F_1 males differed in eye-color from the expected eosin
+vermilion. Since the eosin vermilion and sable stocks were unrelated and
+neither was known to contain a "pink" as an impurity, these "pinks" must be
+due to mutation of an unusual kind. That these "pinks" were really products
+of the cross is proven by the result of crossing one of them to one of her
+eosin vermilion brothers, for she showed herself to be heterozygous for
+eosin, vermilion, and sable.
+
+_F_1 "pink" (Ref. 51 C) [female] x F_1 eosin vermilion [male]._
+
+  +------+---------------+----------------+---------------+---------------+
+  |      |   Wild-type.  |Eosin vermilion.|     Eosin.    |   Vermilion.  |
+  |Refer-+-------+-------+--------+-------+--------+------+--------+------+
+  |ence. |[female]|[male]|[female]|[male] |[female]|[male]|[female]|[male]|
+  +------+-------+------+---------+-------+--------+------+--------+------+
+  |59 C  |   59  |  38  |    43   |   40  |   15   |   9  |   16   |  17  |
+  +------+-------+------+---------+-------+--------+------+--------+------+
+
+In addition to the combinations of eosin and vermilion, sable also appeared
+in its proper distribution though no counts were made. The four smaller
+classes are cross-overs between eosin and vermilion. Since no "pinks"
+appeared the color is recessive, and the brother was not heterozygous for
+it.
+
+Two other "pink" females mated to wild males gave similar results in their
+sons.
+
+_F_1 "pink" [female] x wild [male]._
+
+  +------------+---------+---------+---------+-------+---------+
+  |            |         |         |  Eosin  |       |         |
+  |            |Wild-type|Wild-type|Vermilion| Eosin |Vermilion|
+  | Reference. |[female].| [male]. | [male]. |[male].| [male]. |
+  +------------+---------+---------+---------+-------+---------+
+  | 61 C       |   101   |    33   |    37   |    9  |    11   |
+  +------------+---------+---------+---------+-------+---------+
+
+These F_1 flies should all be heterozygous for "pink." A pair of wild-type
+flies which were mated gave a 3 : 1 ratio--wild type 51 to "pink" 18. From
+the "pinks" which appeared in this cross a stock was made which was lost
+through sterility. Females tested to males of true pink were also sterile,
+so that no solution can be given of the case.
+
+[6] Purple is an eye-color whose gen is in the second chromosome.
+
+[7] The curve published by Miss Stark included by mistake 6 cultures from
+the succeeding generations, and these coming from only one of the lethals
+(lethal _sb_) increase its mode so that the mode of the other lethal
+(lethal _sa_) becomes submerged. If these cultures are taken out the curve
+shows two modes more clearly.
+
+[8] The figures to the left in each double column correspond to the symbols
+above the heavy line, as, in the first example 6,219 white miniature. The
+similar figure to the right corresponds to the symbol below the heavy line.
+If no symbols are present below, as in the first example, the column to the
+right should be read wild-type.
+
+       *       *       *       *       *
+
+
+Changes made against printed original.
+
+Page 24. "two contrary classes, eosin vermilion and bar": 'eosin bar and
+vermilion' in original.
+
+Page 59. "The bristles which are most distorted": 'disorted' in original.
+
+Pages 69-70. One or more lines are missing before "5,352".
+
+Ibid. "The data just given in table 51": 'table 50' in original.
+
+Page 75. "lethal 3_a_ lies at about 19.5.": 'lethal 3' in original.
+
+Page 77. Table 58, last "Facet": 'Fecet' in original.
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Sex-linked Inheritance in Drosophila, by 
+Thomas Hunt Morgan and Calvin B. Bridges
+
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