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diff --git a/34368-8.txt b/34368-8.txt new file mode 100644 index 0000000..e8c2fc9 --- /dev/null +++ b/34368-8.txt @@ -0,0 +1,5376 @@ +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: ISO-8859-1 + +*** 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 rôle 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 Cuénot 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 Cuénot 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 10° 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 larvæ 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] × bifid [male] [male]. B. +C.[2] F_1 wild-type [female] × 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 10° +to 12° 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 × 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 × 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] × sable [male]. F_1 wild-type +[female] [female] × 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] × wild [male] [male]. F_1 wild-type [female] +× 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] × yellow sable [male] [male]. F_1 +wild-type [female] [female] × 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] × yellow sable [male] [male]. B. +C. F_1 wild-type [female] × 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] × sable [male][male]. F_1 wild-type +[female] × 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] × vermilion [male][male]. F_1 +wild-type [female][female] × 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] × 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] × miniature sable [male] [male]. B. +C. F_1 wild-type [female] [female] × 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] × sable bar [male] [male]. B. +C. F_1 bar [female] × 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] × bar [male] [male]. B. +C. F_1 bar [female] × 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] × _sable_ [male] [male]. +_B. C. F_1 bar_ [female] × _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] × _wild_ [male] +[male]. _B. C. F_1 bar_ [female] × _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 × 100 + --------------------------------- = 20.8 + 0.0953 + 0.0028 × 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] × wild [female] [female]. F_1 +wild-type [female] [female] × 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] × 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] × 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] × 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] × 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] × cherry vermilion [male] [male]. F_1 +wild-type [female] × 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] × wild [female] [female]. +F_{1} wild-type [female] [female] × 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] × wild [female] [female]. F_{1} +wild-type [female] [female] × 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] × 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] × 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] × fused [male][male]. F_1 wild-type +[female][female] × 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] × _bar fused_ [male] [male]. +_B. C. F_1 bar_ [female] × _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] × vermilion fused [male] [male]. B. +C. F_1 bar [female] × 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] × fused [male] [male]. F_1 +wild-type [female] [female] × 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] × vermilion fused [male] [male]. F_1 +wild-type [female] × 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 (macrochætæ) 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 macrochætæ, 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] × _vermilion-forked_ [male] [male]. +_F_1 wild-type_ [female] [female] × _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] × _forked_ [male] [male]. +_F_{1} wild-type_ [female] [female] × _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] × _forked fused_ [male] [male]. _B. +C. F_1 bar_ [female] × _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] × _bar fused_ [male] [male]. +_B.C. F_1 bar_ [female] × _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] × _wild_ [female]. +_F_{1} wild-type_ [female] × _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] × _bar_ [female]. _B.C. F_1 bar_ +[female] × _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] × wild [female] [female]. +F_1 wild-type [female] × 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] × _bar_ [male] [male]. _F_1 +bar_ [female] × _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] × _bar_ [female] [female]. +_B.C. F_1 bar_ [female] × _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] × 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] × _vermilion_ [male] [male]. _F_1 +wild-type_ [female] × _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] × _yellow_ [male] [male]. +_F_1 wild-type_ [female] [female] × _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] × _club vermilion_ [male] +[male]. _B. C. F__{1} _wild-type_ [female] × _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] × +_wild_ [male] [male]. _F_{1} wild-type_ [female] × _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] × _wild_ [female] [female]. _B.C. F_1 +wild-type_ [female] × _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] × _vermilion sable_ [female] [female]. _B.C. +F_1 wild-type_ [female] × _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] × _facet_ [male]. _F_1 wild-type_ +[female] × _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 × bifid.| 233 254| 1 2 | 10 6 | .. .. | 506 | + | +========+========+========+========+======+ + | | y | y v B' | y B'| y v | | + | | -------| -+-----| ---+---| -+--+--| | + | | v B'| | v | B'| | + |Yellow × 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 × forked.| 84 77 | 9 6 | 65 59 | 1 5 | 306 | + | +========+========+========+========+======+ + | | v m | v s| v m s| v | | + | | -------| -+-----| ---+---| -+--+--| | + | | s| m | | m s| | + |Vermilion miniature +--------+--------+--------+--------+------+ + |× sable. | 152 111| 4 2 | 5 12 | .. ..| 286 | + | +========+========+========+========+======+ + | | s r | s f| s r f| s | ~ + | | -------| -+-----| ----+--| -+--+--| ~ + | | f| r | | r f| | + |Sable rudimentary × +--------+--------+--------+--------+------+ + |forked. | 143 195| 26 27 | 4 3 | .. ..| 398 | + +---------------------+--------+--------+--------+--------+------+ + | WHITE BIFID × 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 × 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 × RUDIMENTARY. | + +--------------------------------------+ + | Cross-over values. | + +------------+------------+------------+ + | White | Bifid | White | + | bifid. |rudimentary.|rudimentary.| + | | | | + +------------+------------+------------+ + | 3.8 | 42.3 | 44.5 | + +------------+------------+------------+ + | WHITE BIFID × 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 rôle 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] × 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] × 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. 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