Chapter V: Part II: New Data (2)

Only three dot individuals appeared in F_2, but since these were males the result indicates that the dot character is due to a sex-linked gen. These three males had also vermilion eyes, indicating linkage of dot and vermilion. The males show no deficiency in numbers, therefore the non-appearance of the dot can not be due to its being semi-lethal. It appears, therefore, that the expression of the character must depend on the presence of an intensifying factor in one of the autosomes, or more probably, like club, it appears only in a small percentage of flies that are genetically pure for the character.

The reciprocal cross (dot female with vermilion eyes by wild male) was made (table 20). The daughters were wild type and the sons vermilion. Not one of the 272 sons showed dot. If the gen is sex-linked the non-appearance of dot in the F_1 males can be explained on the ground that males that are genetically dot show dot very rarely, or that its appearance is dependent upon the intensification by an autosomal factor of the effect produced by the sex-linked factor for dot.

TABLE 20.--_P_1 vermilion dot [female] x wild [male]._

A = Wild-type [female].
B = Vermilion [male].
C = Wild-type [male].
D = Wild-type [female].
E = Vermilion [male].
F = Vermilion [female].
G = Vermilion dot [male].
H = Vermilion dot [female].
I = Dot [male].
J = Dot [female].

+--------------------++-----------------------------------------------+
| First generation. || Second generation. |
+----------+----+----++----------+----+----+----+----+----+---+---+---+
|Reference.| A | B ||Reference.| C | D | E | F | G | H | I | J |
+--------------------++----------+----+----+----+----+----+---+---+---+
| 137 C. | 44 | 45 || 19 |211 |198 |228 |206 | 20 | 3 | 0 | 0 |
| 138 C. | 77 | 62 || 22 |266 |220 |227 |227 | 16 | 0 | 0 | 0 |
| |124 |124 || 28 |143 |149 |125 |124 | 14 | 1 | 0 | 0 |
| | 57 | 41 || +----+----+----+----+----+---+---+---+
| |----|----|| Total.|620 |567 |570 |557 | 50 | 4 | 0 | 0 |
| Total.|291 |272 || | | | | | | | | |
+--------------------++----------+----+----+----+----+----+---+---+---+

The F_2 generation is given in table 20. The dot reappeared in F_2 both in females and in males, but instead of appearing in 50 per cent of both sexes, as expected if it is simply sex-linked, it appeared in 4.0 per cent in the females and in only 0.4 per cent in the males. The failure of the character to be fully realized is again apparent, but here, where it is possible for it to be realized equally in males and females, we find that there are 50 females with dot to only 4 dot males. This would indicate that the character is partially "_sex-limited_" (Morgan, 1914_d_) in its realization. The dot appeared only in flies with vermilion eyes, indicating extremely strong linkage between vermilion and dot.

The evidence from the history of the stock, together with these experiments, shows that the character resembles club (wing) in that it is not expressed somatically in all the flies which are homozygous for it. In the case of club we were fortunate enough to find a constant feature {46} which we could use as an index, but, so far as we have been able to see, there is no such constant accessory character in the case of the dot. Unlike club, dot is markedly sex-limited in its effect; that is, there is a difference of expression of the gen in the male and female. This difference recalls the sexual dimorphism of the eosin eye.

BOW.

In an F_2 generation from rudimentary males by wild females there appeared, August 15, 1912, a single male whose wings instead of being flat were turned down over the abdomen (fig. c). The curvature was uniform throughout the length of the wing. A previous mutation, arc, of this same type had been found to be a recessive character in the second group. The new mutation, bow, is less extreme than arc and is more variable in the amount of curvature. When the bow male was mated to wild females the offspring had straight wings.

TABLE 21.--_P_1 bow [male][male] x wild [female][female]._

+------------------------------------------+
| First generation. |
+----------+-----------------+-------------+
|Reference.| Wild-type | Wild-type ~
| |[female][female].|[male][male].~
+----------+-----------------+-------------+
| 169 C. | 17 | 17 |
+----------+-----------------+-------------+

+--------------------------------------------------------+
| Second generation. |
+----------+-----------------+-------------+-------------+
~Reference.| Wild-type | Wild-type | Bow |
~ |[female][female].|[male][male].|[male][male].|
+----------+-----------------+-------------+-------------+
| 18 I. | 193 | 145 | 67 |
| 21 I | 182 | 100 | 49 |
| +-----------------+-------------+-------------+
| Total.| 375 | 245 | 116 |
+----------+-----------------+-------------+-------------+

{47}

The F_2 ratio in table 21 is evidently the 2:1:1 ratio typical of sex-linkage, but with the bow males running behind expectation. This deficiency is due in part to viability but more to a failure to recognize all the bow-winged individuals, so that some of them were classified among the not-bow or straight wings. In favor of the view that the classification was not strict is the fact that the sum of the two male classes about equals the number of the females.

BOW BY ARC.

When this mutant first appeared its similarity to arc led us to suspect that it might be arc itself or an allelomorph of arc. It was bred, therefore, to arc. The bow male by arc females gave straight (normal) winged males and females. The appearance of straight wings shows that bow is not arc nor allelomorphic to arc. When made later, the reciprocal cross of bow female by arc male gave in F_1 straight-winged females but bow males. This result is in accordance with the interpretation that bow is a sex-linked recessive. Further details of these last two experiments may now be given. The F_1 (wild-type) flies from bow male by arc female were inbred. The data are given in table 22.

TABLE 22.--_P_1 bow [male] x arc [female]._

+--------------------------------------------+
| First generation. |
+----------+------------------+--------------+
|Reference.| Wild-type | Wild-type ~
| |[female] [female].|[male] [male].~
+----------+------------------+--------------+
| 71 C. | 48 | 43 |
| 75 C. | 28 | 27 |
| +------------------+--------------+
| Total.| 76 | 70 |
+----------+------------------+--------------+

+------------------------------+
| Second generation. |
+----------+---------+---------+
~Reference.|Straight.| Not- |
~ | |straight.|
+----------+---------+---------+
| 71 C. | 179 | 133 |
+----------+---------+---------+

Bow and arc are so much alike that they give a single rather variable phenotypic class in F_2. Therefore the F_2 generation is made up of only two separable classes--flies with straight wings and flies with not-straight wings. The ratio of the two should be theoretically 9:7, which is approximately realized in 179:133.

If the distribution of the characters according to sex is ignored, the case is similar to the case of the two white races of sweet peas, which bred together gave wild-type or purple peas in F_1 and in F_2 gave 9 colored to 7 white. If sex is taken into account, the theoretical expectation for the F_2 females is 6 straight to 2 arc, and for the F_2 males 3 straight to 1 arc to 3 bow to 1 bow-arc.

The F_1 from bow females by arc male and their F_2 offspring are given in table 23. {48}

TABLE 23.--_P_1 bow [female] x arc [male]._

+--------------------------------------------+
| First generation. |
|----------+------------------+--------------+
|Reference.| Wild-type | Bow |
| |[female] [female].|[male] [male].|
|----------+------------------+--------------+
| 72 C. | 22 | 19 ~
| 73 C. | 12 | 10 ~
| 5 I. | 22 | 21 |
| 74 C. | 56 | 52 |
| |------------------+--------------+
| Total.| 112 | 102 |
+----------+------------------+--------------+

+------------------------------+
| Second generation. |
+----------+---------+---------+
|Reference.|Straight.| Not- |
| | |straight.|
+----------+---------+---------+
~ 3 I. | 56 | 69 |
~ 3.1 I. | 46 | 62 |
| 5 I. | 56 | 68 |
| 5.1 I. | 90 | 108 |
+----------+---------+---------+
| Total.| 248 | 307 |
+----------+---------+---------+

In this case the F_2 expectation is 6 straight to 10 not-straight. Since the sex-linked gen bow entered from the female, half the F_2 males and females are bow. The half that are not-bow consist of 3 straight to 1 arc, so that both in the female classes and in the male classes there are 3 straight to 5 not-straight or in all 6 straight to 10 not-straight. The realized result, 248 straight to 307 not-straight, is more nearly a 3:4 ratio, due probably to a wrong classification of some of the bow as straight.

LEMON BODY-COLOR.

(Plate I, figure 3.)

A few males of a new mutant with a lemon-colored body and wings appeared in August 1912. The lemon flies (Plate II, fig. 3) resemble quite closely the yellow flies (Plate II, fig. 4). They are paler and the bristles, instead of being brown, are black. These flies are so weak that despite most careful attention they get stuck to the food, so that they die before mating. The stock was at first maintained in mass from those cultures that gave the greatest percentage of lemon flies. In a few cases lemon males mated with their gray sisters left offspring, but the stock obtained in this way had still to be maintained by breeding heterozygotes, as stated above. But from the gray sisters heterozygous for lemon (bred to lemon males) some lemon females were also produced.

LINKAGE OF CHERRY, LEMON, AND VERMILION.

In order to study the linkage of lemon, the following experiment was carried out. Since it was impracticable to breed directly from the lemon flies, virgin females were taken from stock throwing lemon, and were mated singly to cherry vermilion males. Only a few of the females showed themselves heterozygous for lemon by producing lemon as well as gray sons. Half the daughters of such a pair are expected to be heterozygous for lemon and also for cherry and vermilion, which went in from the father. These daughters were mated singly to cherry vermilion males, and those that gave some lemon sons were continued, {49} and are recorded in table 24. The four classes of females were not separated from each other, but the total of females is given in the table.

TABLE 24.--_P_1 lemon (het.) [female] x cherry vermilion [male] [male]. F_1 wild-type [female] x cherry vermilion [male] [male]._

+-------+--------------+-------------+-------------+-------------+------+
| | W^c V | W^c l_m | W^c | W^c l_m V | |
| | ---------- | ---+------ | ------+--- | ---+----+---| |
| | l_m | V | l_m V | | |
|Females+-------+------+------+------+------+------+-------+-----+ Total|
| |Cherry | |Cherry| Ver- |Cherry|Lemon |Cherry |Wild |[male]|
| | ver- |Lemon.|lemon.|milion| | ver- |lemon |type.|[male]|
| |milion.| | | | |milion| ver- | | |
| | | | | | | |milion.| | |
+-------+-------+------+------+------+------+------+-------+-----+------+
| 71 | 42 | 19 | 2 | 6 | 3 | 6 | 0 | 0 | 78 |
| 88 | 26 | 19 | 2 | 8 | 8 | 4 | 0 | 0 | 67 |
| 36 | 28 | 7 | 0 | 2 | 1 | 0 | 0 | 0 | 38 |
| 51 | 12 | 22 | 0 | 4 | 4 | 4 | 0 | 0 | 46 |
| 98 | 29 | 35 | 0 | 8 | 5 | 1 | 0 | 0 | 78 |
| 47 | 17 | 11 | 0 | 1 | 3 | 2 | 0 | 0 | 34 |
| 46 | 23 | 20 | 1 | 6 | 5 | 2 | 0 | 0 | 57 |
+-------+-------+------+------+------+------+------+-------+-----+------+
| 437 | 177 | 133 | 5 | 35 | 29 | 19 | 0 | 0 | 398 |
+-------+-------+------+------+------+------+------+-------+-----+------+

There are three loci involved in this cross, namely, cherry, lemon, and vermilion. Of these loci two were known, cherry and vermilion. The data are consistent with the assumption that the lemon locus is between cherry and vermilion, for the double cross-over classes (the smallest classes) are cherry lemon vermilion and wild type. The number of single cross-overs between cherry and lemon and between lemon and vermilion are also consistent with this assumption. Since lemon flies fail to emerge successfully, depending in part upon the condition of the bottle, the classes involving lemon are worthless in calculating crossing-over and are here ignored. In other words, lemon may be treated as though it did not appear at all, _i. e._, as a lethal. The not-lemon classes--cherry, vermilion, cherry vermilion, and wild type--give the following approximate cross-over values for the three loci involved: Cherry lemon, 15; lemon vermilion, 12; cherry vermilion, 27. The locus of lemon, calculated by interpolation, is at about 17.5.

LETHAL 2.

In September 1912 a certain wild female produced 78 daughters and only 16 sons (Morgan, 1914_b_); 63 of these daughters were tested and 31 of them gave 2 females to 1 male, while 32 of them gave 1:1 sex-ratios. This shows that the mother of the original high sex-ratio was heterozygous for a recessive sex-linked lethal. In order to determine the position of this lethal, a lethal-bearing female was bred to an eosin (or white) miniature male, and those daughters that were heterozygous for eosin, lethal, and miniature were then back-crossed to {50} eosin miniature males. The daughters that result from such a cross give only the amount of crossing-over between eosin and miniature (as 29.7), but the males give the cross-over values for eosin lethal (9.9), lethal miniature (15.4), and eosin miniature (25.1). The data for this cross are given in table 25.

TABLE 25.--_Total data upon linkage of eosin, lethal 2, and miniature, from Morgan, 1914b._

+------------------------------------+
| Females. |
+--------+--------------+------------+
| | | |
| Total. | Cross-overs. | Cross-over |
| | | value. ~
| | | ~
+--------+--------------+------------+
| 15,904 | 4,736 | 29.7 |
+--------+--------------+------------+

+-----------------------------------------------------------------------+
| Males. |
+--------+--------+--------+---------+----------------------------------+
|w^e m|w^e l_2 |w^e |w^e l_2 m| Cross-over values. |
|--------|---+----|------+-|---+---+-+----------+-----------+-----------+
~ l_2 | m| l_2 m| | Eosin | Lethal 2 | Eosin |
~ | | | | lethal 2.| miniature.| miniature.|
+--------+--------+--------+---------+----------+-----------+-----------+
| 5,045 | 653 | 1,040 | 14 | 9.9 | 15.4 | 25.1 |
+--------+--------+--------+---------+----------+-----------+-----------+

A similar experiment, in which eosin and vermilion were used instead of eosin and miniature, is summarized in table 26.

TABLE 26.--_Total data upon the linkage of eosin, lethal 2, and vermilion, from Morgan, 1914b._

+------------------------------------+
| Females. |
+--------+--------------+------------+
| | | |
| Total. | Cross-overs. | Cross-over |
| | | value. ~
| | | ~
+--------+--------------+------------+
| 2,656 | 729 | 27.5 |
+--------+--------------+------------+

+-----------------------------------------------------------------------+
| Males. |
+--------+--------+--------+---------+----------------------------------+
|w^e v|w^e l_2 |w^e |w^e l_2 v| Cross-over values. |
|--------|---+----|------+-|---+---+-+----------+-----------+-----------+
~ l_2 | v| l_2 v| | Eosin | Lethal 2 | Eosin |
~ | | | | lethal 2.| vermilion.| vermilion.|
+--------+--------+--------+---------+----------+-----------+-----------+
| 902 | 124 | 227 | 6 | 10.3 | 18.5 | 27.9 |
+--------+--------+--------+---------+----------+-----------+-----------+

Considerable data in which lethal was not involved were also obtained in the course of these experiments and are included in the summary of the total data given in table 27.

TABLE 27.--_Summary of all data upon lethal 2, from Morgan, 1914b._

+--------------------+--------+--------------+------------+
| Gens. | Total. | Cross-overs. | Cross-over |
| | | | values. |
+--------------------+--------+--------------+------------+
| White lethal 2 | 8,011 | 767 | 9.6 |
| White vermilion | 6,023 | 1,612 | 26.8 |
| White miniature | 36,021 | 11,048 | 30.7 |
| Lethal 2 vermilion | 1,400 | 248 | 17.7 |
| Lethal 2 miniature | 6,752 | 1,054 | 15.4 |
+--------------------+--------+--------------+------------+

The amount of crossing-over between eosin and lethal is about 10 per cent and the amount of crossing-over between lethal and miniature is about 18 per cent. Since the amount of crossing-over between eosin {51} and miniature is over 30 per cent, the lethal factor must lie between eosin and miniature, somewhat nearer to eosin. It is impossible at present to locate lethal 2 accurately because of a real discrepancy in the data, which makes it appear that lethal 2 extends for a distance of about 5 units along the chromosome from about 10 to about 15. Work is being done which it is hoped will make clear the reason for this. For the present we may locate lethal 2 at the midpoint of its range, or at 12.5.

CHERRY.

(Plate II, figure 9.)

The origin of the eye-color cherry has been given by Safir (Biol. Bull., 1913).

Cherry appeared (October 1912) in an experiment involving vermilion eye-color and miniature wings. This is the only time the mutant has ever come up, and although several of this mutant (males) appeared in Safir's experiment, they may have all come from the same mother. It is probable that the mutation occurred in the vermilion stock only a generation or so before the experiment was made, for otherwise cherry would be expected to be found also in the vermilion stock from which the mothers were taken; however, it was not found.

A SYSTEM OF QUADRUPLE ALLELOMORPHS.

Safir has described crosses between this eye-color and red, white, eosin, and vermilion. We conclude for reasons similar to those given by Morgan and Bridges (Jour. Exp. Zool., 1913) for the case of white and eosin, that cherry is an allelomorph of white and of eosin. This is not the interpretation followed in Safir's paper, where cherry is treated as though absolutely linked to white or to eosin. Both interpretations give, however, the same numerical result for each cross considered by itself. Safir's data and those which appear in this paper show that white, eosin, cherry, and a normal (red) allelomorph form a system of quadruple allelomorphs. If this interpretation is correct, then the linkage relations of cherry should be identical with those of white or of eosin.

LINKAGE OF CHERRY AND VERMILION.

The cross-over value for white (eosin) and vermilion, based on a very large amount of data, is about 31 units. An experiment of our own in which cherry was used with vermilion gave a cross-over value of 31 units, which is a close approximation to the cross-over value of white and vermilion. The cross which gave this data was that of a cherry vermilion (double recessive) male by wild females. The F_{1} wild-type flies inbred gave a single class of females (wild-type) and the males in four classes which show by the deviation from a 1:1:1:1 ratio the amount of crossing-over involved. {52}

In one of the F_{2} male classes of table 28 the simple eye-color cherry appeared for the first time (since the original mutant was vermilion as well as cherry). Safir has recorded a similar cross with like results.

TABLE 28.--_P_{1} cherry vermilion [male] [male] x wild [female] [female]. F_{1} wild-type [female] [female] x F_{1} wild-type [male] [male]._

+----------+---------+----------------+---------------+-------+------+
| | | Non-cross-over | Cross-over | | |
| | | [male]. | [male]. | | |
| |Wild-type+----------+-----+-------+-------+Total |Cross-|
|Reference.|[female] | Cherry |Wild-|Cherry.| Ver- |[male] |over |
| |[female].|vermilion.|type.| |milion.|[male].|value.|
+----------+---------+----------+-----+-------+-------+-------+------+
| 160 C | 188 | 57 | 61 | 32 | 34 | 184 | 36 |
| 161 C | 256 | 85 | 93 | 40 | 52 | 270 | 34 |
| 162 C | 251 | 78 | 78 | 20 | 37 | 213 | 26 |
| 163 C | 229 | 76 | 95 | 34 | 33 | 238 | 28 |
+----------+---------+----------+-----+-------+-------+-------+------+
| Total | 924 | 296 | 327 | 126 | 156 | 905 | 31 |
+----------+---------+----------+-----+-------+-------+-------+------+

Some cherry males were bred to wild females. The F_{1} wild-type males and females inbred gave the results shown in table 29. Some of the cherry males thus produced were bred to their sisters. Cherry females as well as males resulted; and it was seen that the eye-color is the same in the males and females, in contradistinction to the allelomorph eosin, where there is a marked bicolorism (figs. 7, 8, Plate II). The cherry eye-color is almost identical with that of the eosin female, but is perhaps slightly more translucent and brighter.

TABLE 29.--_P_{1} cherry [male] [male] x wild [female] [female]. F_{1} wild-type [female] [female] x F_{1} wild-type [male] [male]._

+------------+---------------------+-------------------+----------------+
| Reference. | Wild-type [female]. | Wild-type [male]. | Cherry [male]. |
+------------+---------------------+-------------------+----------------+
| 15 I | 266 | 120 | 100 |
+------------+---------------------+-------------------+----------------+

+------------+-------------------------------------+
| | First generation. |
| Reference. +--------------------+----------------+
| | White-cherry | |
| | compound [female]. | Cherry [male]. |
+------------+--------------------+----------------+
| 9 M | 321 | 302 |
+------------+--------------------+----------------+

Eosin-cherry compound was also made. An eosin female was mated to a cherry male. The eosin-cherry daughters were darker than their eosin brothers. Inbred they gave the results shown in table 31.

TABLE 31.--_P_1 eosin [female] x cherry [male]._

+------------------------------------------+
| First generation. |
+------------+-------------------+---------+
| | Eosin-cherry | Eosin |
| Reference. | compound | [male] |
| | [female][female]. | [male]. ~
| | | ~
+------------+-------------------+---------+
| 43C | 71 | 58 |
+------------+-------------------+---------+

+----------------------------------------------------+
| Second generation. |
+------------+-------------------+---------+---------+
| | Eosin and | | |
| Reference. | eosin-cherry | Cherry | Eosin |
~ | compound | [male]. | [male]. |
~ | [female][female]. | | |
+------------+-------------------+---------+---------+
| 1I | 154 | 99 | 62 |
| 2I | 174 | 74 | 77 |
| +-------------------+---------+---------+
| | 328 | 173 | 139 |
+------------+-------------------+---------+---------+

Although in the F_2 results there are two genotypic classes of females, namely, pure eosin and eosin-cherry compound, the eye-colors are so nearly the same that they can not be separated. The two classes of males can be readily distinguished; of these, one class, cherry, has the same color as the females, while the other class, eosin, is much lighter. Such an F_2 group will perpetuate itself, giving one type of female (of three possible genotypic compositions, but somatically practically homogeneous) and two types of males, only one of which is like the females.

FUSED.

In a cross between purple-eyed[6] males and black females there appeared in F_2 (Nov. 4, 1912) a male having the veins of the wing arranged as shown in text-figure D b. It will be seen that the third and the fourth longitudinal veins are fused from the base to and beyond the {53} point at which in normal flies the anterior cross-vein lies. The cross-vein and the cell normally cut off by it are absent. There are a number of other features (see fig. D _c_) characteristic of this mutation: the wings are held out at a wide angle from the body, the ocelli are very much reduced in size or entirely absent, the bristles around the ocelli are usually small. The females are absolutely sterile, not only with their own, but with any males.

Fused males by wild females gave wild-type males and females. Inbred these gave the results shown in table 32. The fused character reappeared only in the F_2 males, showing that it is a recessive sex-linked character.

TABLE 32.--_P_1 fused [male] x wild [female][female]._

+-------------------------------------------------+
| First generation. |
+------------+-------------------+----------------+
| Reference. | Wild-type | Wild-type ~
| | [female][female]. | [male][male]. ~
+------------+-------------------+----------------+
| 4I | 66 | 43 |
| | | |
+------------+-------------------+----------------+

+------------------------------------------------------------------+
| Second generation. |
+------------+-------------------+----------------+----------------+
~ Reference. | Wild-type | Wild-type | Fused |
~ | [female][female]. | [male][male]. | [male][male]. |
+------------+-------------------+----------------+----------------+
| 190C | 258 | 96 | 115 |
| 14I | 239 | 105 | 90 |
| +-------------------+----------------+----------------+
| Total | 497 | 201 | 205 |
+------------+-------------------+----------------+----------------+

The reciprocal cross was tried many times, but is impossible, owing to the sterility of the females. Since the fused females are sterile to fused males, the stock is kept up by breeding heterozygous females to fused males.

By means of the following experiments the position of fused in the X chromosome was determined. A preliminary test was made by mating with eosin, whose factor lies near the left end of the X chromosome series.

LINKAGE OF EOSIN AND FUSED.

Fused (red-eyed) males mated to eosin (not-fused) females gave wild-type daughters and eosin sons, which inbred gave the classes shown in table 33.

TABLE 33.--_P_1 eosin [female][female] x fused [male][male]. F_1 wild-type [female][female] x F_1 eosin [male][male]._

+----------+--------+-----------------+----------------+-------+--------+
| | | Non-cross-over | Cross-over | | |
| | | [male][male]. | [male][male]. | Total | Cross- |
|Reference.|Females.+--------+--------+--------+-------+ males.| over |
| | | Eosin. | Fused. | Eosin | Wild- | | value. |
| | | | | fused. | type. | | |
+----------+--------+--------+--------+--------+-------+-------+--------+
| 56I | 496 | 131 | 113 | 82 | 104 | 430 | 43 |
+----------+--------+--------+--------+--------+-------+-------+--------+

{54}

The data give 43 per cent of crossing-over, which places fused far to the right or to the left of eosin. The latter position is improbable, since eosin already lies very near the extreme left end of the known series. Therefore, since 43 per cent would place the factor nearly at the right end of the series, the next step was to test its relation to a factor like bar that lies at the right end of the chromosome. By mating to bar alone we could only get the linkage to bar without discovering on which side of bar the new factor lies, but by mating to a fly that carries still another sex-linked factor, known to lie to the left of bar, the information gained should show the relative order of the factors involved. Furthermore, since, by making a back-cross, both males and females give the same kind of data (and need not be separated), the experiment was made in this way. In order to have material for such an experiment double mutant stocks of vermilion fused and also of bar fused were made up.

{55}

LINKAGE OF VERMILION, BAR, AND FUSED.

Males from the stock of (red) bar fused were mated to vermilion (not-bar, not-fused) females, and produced bar females and vermilion males. The bar F_1 daughters were back-crossed to vermilion fused males and produced the classes of offspring shown in table 34.

TABLE 34.--P_1 _vermilion_ [female] [female] x _bar fused_ [male] [male]. _B. C. F_1 bar_ [female] x _vermilion fused_ [male] [male].

+----------+-------------------+---------------------+------------------+
| | v | v B' f_u | v f_u |
| | ----------------- | ----+-------------- | -----------+---- |
| | B' f_u | | B' |
|Reference.+----------+--------+----------+----------+-----------+------+
| | | | Vermilion| | | |
| |Vermilion.| Bar | bar |Wild-type.| Vermilion | Bar. |
| | | fused. | fused. | | fused. | |
+----------+----------+--------+----------+----------+-----------+------+
|140 I | 137 | 130 | 35 | 40 | 5 | 8 ~
|141 I | 144 | 137 | 38 | 41 | 4 | 2 ~
|142 I | 153 | 120 | 43 | 58 | 6 | 7 |
|143 I | 153 | 92 | 44 | 41 | 3 | 7 |
|145 I | 69 | 62 | 29 | 19 | 1 | .. |
|146 I | 96 | 103 | 30 | 34 | 7 | 3 |
|156 I | 62 | 45 | 25 | 27 | 1 | 4 |
|157 I | 93 | 57 | 11 | 31 | 2 | 2 |
| +----------+--------+----------+----------+-----------+------+
| Total. | 907 | 746 | 255 | 291 | 29 | 33 |
+----------+----------+--------+----------+----------+-----------+------+

+--------------------+--------+--------------------------------+
| v B' | | |
| ----+--------+---- | | Cross-over values. |
| f_u | | |
+-----------+--------+ +-----------+--------+-----------+
| | | Total. | | | |
| Vermilion | Fused. | | Vermilion | Bar | Vermilion |
| bar. | | | bar. | fused. | fused. |
+-----------+--------+--------+-----------+--------+-----------+
~ .. | .. | 355 | 21 | 4 | 25 |
~ .. | .. | 366 | 22 | 2 | 23 |
| 1 | .. | 388 | 26 | 4 | 29 |
| 3 | 1 | 344 | 26 | 4 | 28 |
| 1 | .. | 181 | 27 | 1 | 27 |
| .. | .. | 273 | 23 | 4 | 26 |
| .. | .. | 164 | 32 | 3 | 35 |
| .. | 2 | 198 | 22 | 3 | 23 |
+-----------+--------+--------+-----------+--------+-----------+
| 5 | 3 | 2,269 | 24 | 3 | 27 |
+-----------+--------+--------+-----------+--------+-----------+

The data show that the factor for fused lies about 3 units to the right of bar. This is the furthest point yet obtained to the right. The reasons for locating fused to the right of bar are that, if it occupies such a position, then the double cross-over classes (which are expected to be the smallest classes) should be vermilion bar and fused, and these are, in fact, the smallest classes. The order of factors is, then, vermilion, bar, fused. This order is confirmed by the result that the number of cross-overs between fused and vermilion is greater than that between bar and vermilion.

In order to obtain data to balance viability effects, the following experiment was made:

Vermilion (not-bar) fused males were bred to (red) bar (not-fused) females. The daughters and sons were bar. The daughters were back-crossed, singly, to vermilion fused males and gave the results shown in table 35. Each female was also transferred to a second culture bottle, so that for each female there are two broods given consecutively (82, 82', etc.) in table 35.

The results given by the two broods of the same female are similar. The values are very near to those given in the last experiment, and confirm the conclusions there drawn. The combined data give the results shown in table 36. {56}

TABLE 35.--_P_1 bar [female] [female] x vermilion fused [male] [male]. B. C. F_1 bar [female] x vermilion fused [male] [male]._

A - Vermilion fused.
B - Bar.
C - Vermilion bar.
D - Fused.
E - Vermilion.
F - Bar fused.
G - Vermilion bar fused.
H - Wild type.

-------------------------------------------------------------------------
| v f_u | v B' |v |v B' f_u| | Cross-
| -------- |----+----|----+----|-+---+---| | over
| B' | f_u | B' f_u | |Total.| values.
Reference +-------------+---------+---------+---------+ +-----------
| A | B | C | D | E | F | G | H | | C | F | A
----------+------+------+----+----+----+----+----+----+------+---+---+---
| | | | | | | | | | | |
82 | 165 | 165 | 63 | 57 | 8 | 7 | 1 | .. | 466 | 26|3 | 29
82' | 104 | 87 | 26 | 24 | .. | 4 | .. | .. | 245 | 20|2 | 22
83 | 128 | 164 | 51 | 39 | 6 | 4 | .. | .. | 392 | 23|3 | 26
83' | 100 | 94 | 28 | 30 | 4 | 4 | .. | .. | 260 | 22|3 | 25
89 | 85 | 105 | 23 | 24 | 5 | 2 | .. | .. | 244 | 19|3 | 22
89' | 78 | 91 | 21 | 27 | 1 | 2 | .. | 1 | 221 | 22|2 | 23
90 | 86 | 85 | 30 | 28 | 5 | .. | .. | .. | 234 | 25|2 | 27
90' | 33 | 38 | 22 | 14 | 4 | 1 | .. | 1 | 113 | 33|5 | 36
91 | 125 | 107 | 41 | 31 | 1 | 1 | .. | .. | 306 | 24|1 | 24
91' | 91 | 95 | 31 | 25 | 5 | 1 | .. | 2 | 250 | 23|3 | 25
92 | 109 | 136 | 41 | 24 | 4 | 2 | .. | .. | 316 | 21|2 | 23
92' | 100 | 105 | 29 | 29 | .. | 1 | .. | 1 | 265 | 22|1 | 22
93 | 75 | 67 | 19 | 20 | .. | 1 | .. | .. | 182 | 21|1 | 22
93' | 68 | 94 | 31 | 17 | 1 | 1 | .. | .. | 212 | 23|1 | 24
94 | 84 | 96 | 31 | 35 | 8 | 1 | .. | .. | 255 | 26|4 | 29
94' | 61 | 73 | 20 | 22 | 5 | 4 | .. | .. | 185 | 23|5 | 28
95 | 84 | 102 | 27 | 26 | 3 | 3 | .. | .. | 245 | 22|2 | 24
96 | 144 | 148 | 43 | 34 | 1 | 2 | .. | 1 | 373 | 21|1 | 21
97 | 81 | 96 | 25 | 20 | 5 | 3 | .. | .. | 230 | 20|4 | 23
98 | 107 | 112 | 39 | 33 | 1 | 2 | .. | .. | 294 | 25|1 | 26
Firsts |1,273 |1,383 |433 |371 | 47 | 28 | 1 | 1 |3,537 | 23|2 | 25
Seconds | 635 | 677 |208 |188 | 20 | 18 | .. | 5 |1,751 | 23|3 | 25
----------+------+------+----+----+----+----+----+----+------+---+---+---
Total.|1,908 |2,060 |641 |559 | 67 | 46 | 1 | 6 |5,288 | 23|2.3| 25
----------+------+------+----+----+----+----+----+----+------+---+---+---

TABLE 36.--_Linkage of vermilion, bar, and fused with balanced viability._

+------------+----------+-----------+-----------+-----------+--------+
| | v B' f_u | v | v B' | v f_u | |
| | -------- | --+------ | -----+--- | -+---+--- | Total. |
| | | B' f_u | f_u | B' | |
+------------+----------+-----------+-----------+-----------+--------+
| | | | | | |
| | 5,621 | 1,756 | 175 | 15 | 7,567 |
| Percentage | 74.3 | 23.19 | 2.31 | 0.2 | |
| | | | | | |
+------------+----------+-----------+-----------+-----------+--------+

Some additional data bearing on the linkage of vermilion and fused were obtained. Males of (red) fused stock were bred to vermilion (not-fused) females, and gave wild-type females and vermilion males, which inbred gave the results shown in table 37.

The percentage of cross-overs between vermilion and fused is here 27, which is in agreement with the 26 per cent of the preceding experiment.

The converse experiment, namely, red (not-fused) females by vermilion fused males also gave, when the wild-type daughters were {57} back-crossed to vermilion fused males, a linkage value of 27 units. Two 10-day broods were reared from each female. The data given in table 38 show that the percentage of crossing-over does not change as the flies get older. The locus of fused on the basis of all of the data is at 59.5.

TABLE 37.--P_1 vermilion [female] [female] x fused [male] [male]. F_1 wild-type [female] [female] x F_1 vermilion [male] [male].

KEY:
A: Non-cross-over [male] [male].
B: Cross-over [male] [male].
C: Females.
D: Vermilion.
E: Fused.
F: Vermilion fused.
G: Wild-type.
H: Total [male] [male].
I: Cross-over values.

+------------+-----+-----------+----------+-----+----+
| | | A | B | | |
| | +-----+-----+----+-----+ | |
| Reference. | C | D | E | F | G | H | I |
+------------+-----+-----+-----+----+-----+-----+----+
| 79 I | 299 | 93 | 96 | 37 | 36 | 262 | 28 |
| 80 I | 245 | 93 | 60 | 28 | 27 | 208 | 26 |
| 81 I | 263 | 101 | 63 | 22 | 40 | 226 | 27 |
| +-----+-----+-----+----+-----+-----+----+
| Total. | 807 | 287 | 219 | 87 | 103 | 696 | 27 |
+------------+-----+-----+-----+----+-----+-----+----+

TABLE 38.--P_1 wild [female] [female] x vermilion fused [male] [male]. F_1 wild-type [female] x F_1 wild-type [male] [male].

KEY:
A: Wild-type [female] [female].
B: Non-Cross-over [male].
C: Cross-over [male].
D: Vermilion fused.
E: Wild-type.
F: Vermilion.
G: Fused.
H: Total [male] [male].
I: Cross-over values.

+------------+-------+------------+-----------+-----+----+
| | | B | C | | |
| | +-----+------+-----+-----+ | |
| Reference. | A | D | E | F | G | H | I |
+------------+-------+-----+------+-----+-----+-----+----+
| 52 | 96 | 25 | 30 | 16 | 11 | 82 | 33 |
| 52' | 176 | 59 | 64 | 24 | 19 | 166 | 26 |
| 53 | 60 | 20 | 22 | 9 | 6 | 57 | 26 |
| 53' | 76 | 21 | 27 | 11 | 10 | 69 | 31 |
| 54 | 88 | 35 | 38 | 14 | 16 | 103 | 29 |
| 54' | 60 | 22 | 20 | 8 | 9 | 59 | 29 |
| 57 | 61 | 22 | 20 | 7 | 11 | 60 | 30 |
| 57' | 170 | 47 | 54 | 24 | 19 | 144 | 30 |
| 58 | 128 | 37 | 55 | 14 | 10 | 116 | 21 |
| 58' | 144 | 38 | 64 | 16 | 15 | 133 | 23 |
| Firsts | 433 | 139 | 165 | 60 | 54 | 418 | 27 |
| Seconds | 626 | 187 | 229 | 83 | 72 | 571 | 27 |
| +-------+-----+------+-----+-----+-----+----+
| Total | 1,059 | 326 | 394 | 143 | 126 | 989 | 27 |
+------------+-------+-----+------+-----+-----+-----+----+

FORKED.

On November 19, 1912 there appeared in a stock of a double recessive eye-color, vermilion maroon, a few males which showed a novel form of the large bristles (macrochaetae) upon the head and thorax. In this mutation (text-fig. E) the first of several which affect the shape and distribution of the bristles, the macrochaetae, instead of {58} being long, slender, and tapered (see Plate 1, fig. I), are greatly shortened and crinkled as though scorched. The ends are forked or branched, bent sharply, or merely thickened. The bristles which are most distorted are those upon the scutellum, where they are sometimes curled together into balls.

LINKAGE OF VERMILION AND FORKED.

Since forked arose in vermilion stock, the double recessive for these two sex-linked factors could be used in testing the linkage relations of the mutation. Vermilion forked males were crossed to wild females and gave wild-type males and females, which inbred gave in F_2 the results shown in table 39. Forked reappeared only in the males in the following proportion: not-forked [female], 742; not-forked [male], 346; forked [male], 301. The result shows that the character is a sex-linked recessive.

TABLE 39.--_P_1 wild_ [female] [female] x _vermilion-forked_ [male] [male]. _F_1 wild-type_ [female] [female] x _F_1 wild-type_ [male] [male].

+----------+----------+----------------+---------------+--------+-------+
| | | Non-cross-over | Cross-over | | |
| |Wild-type | [male] [male]. | [male] [male].| Total |Cross- |
|Reference.|[female] +--------+-------+-------+-------+ [male] | over |
| |[female]. | Ver- |Wild- | Ver- |Forked.| [male].|values.|
| | | milion |type. |milion.| | | |
| | | forked.| | | | | |
+----------+----------+--------+-------+-------+-------+--------+-------+
| 9 I | 366 | 113 | 123 | 49 | 41 | 326 | 28 |
| 11 I | 376 | 116 | 150 | 42 | 31 | 339 | 22 |
| +----------+--------+-------+-------+-------+--------+-------+
| Total.| 742 | 229 | 273 | 91 | 72 | 665 | 25 |
+----------+----------+--------+-------+-------+-------+--------+-------+

In table 39 vermilion forked and wild-type are non-cross-overs, and vermilion and forked are cross-overs, giving a cross-over value of 25 units. The locus, therefore, is 25 units to the right or to the left of vermilion, that is, either about 58 or 8 units from the yellow locus.

LINKAGE OF CHERRY AND FORKED.

Forked males were crossed to cherry females (cherry has the same locus as white, which is about 1 unit from yellow) and gave wild-type females and cherry males. These gave in F_2 the results shown in table 40. The non-cross-overs (cherry and forked) plus the cross-overs (cherry forked and wild type) divided into the cross-overs give a cross-over value of 46 units, which shows that the locus lies to the right of vermilion, because if it had been to the left, the value would have been 8 (_i. e._, 33-25) instead of 33+25=58. The difference between 58 {59} and 46 is due to the expected amount of double crossing-over. In fact, for a distance as long as 58 an almost independent behavior of linked gens is to be expected.

TABLE 40.--_P_{1} cherry_ [female] [female] x _forked_ [male] [male]. _F_{1} wild-type_ [female] [female] x _F_{1} cherry_ [male] [male].

+----------+--------------+---------------+-------------+-------+-------+
|Reference.| Females. | Non-cross-over| Cross-over | | |
| | | [male] [male].|[male] [male]| Total |Cross- |
| +-------+------+-------+-------+-------+-----+[male] | over |
| |Cherry.| Wild-|Cherry.|Forked.|Cherry |Wild-|[male].|values.|
| | | type.| | |forked.|type.| | |
+----------+-------+------+-------+-------+-------+-----+-------+-------+
| 25 | 129 | 145 | 73 | 70 | 65 | 68 | 276 | 48 |
| 25' | 167 | 148 | 74 | 82 | 66 | 88 | 310 | 50 |
| 36 | 96 | 88 | 52 | 52 | 35 | 51 | 190 | 45 |
| 36' | 57 | 76 | 41 | 32 | 24 | 30 | 127 | 43 |
| 84 | 76 | 86 | 40 | 34 | 38 | 26 | 138 | 46 |
| 84' | 62 | 71 | 24 | 39 | 25 | 28 | 116 | 46 |
| 85 | 114 | 86 | 43 | 78 | 41 | 53 | 215 | 44 |
| 85' | 98 | 95 | 48 | 63 | 52 | 46 | 209 | 47 |
| 86 | 307 | 323 | 152 | 144 | 118 | 165 | 579 | 49 |
| 87 | 351 | 341 | 183 | 213 | 160 | 147 | 703 | 45 |
| 88 | 244 | 246 | 142 | 142 | 107 | 104 | 495 | 43 |
+----------+-------+------+-------+-------+-------+-----+-------+-------+
|Total. | 1,701 |1,705 | 872 | 949 | 731 | 806 |3,358 | 46 |
+----------+-------+------+-------+-------+-------+-----+-------+-------+

LINKAGE OF FORKED, BAR, AND FUSED.

This value of 58 gave the furthest locus to the right obtained up to that time, since forked is slightly beyond rudimentary. Later, the locus for bar-eye was found still farther to the right, and the locus for fused even farther to the right than bar. A cross was made involving these three gens. A forked (not-bar) fused male was bred to a (not-forked) bar (not-fused) female and gave bar females and males. The F_1 females were back-crossed singly to forked fused males with the result shown in table 41.

TABLE 41.--_P_1 bar_ [female] [female] x _forked fused_ [male] [male]. _B. C. F_1 bar_ [female] x _forked fused_ [male] [male].

+-------+------------+-------------+--------------+-------------+-------+
| | f f_u | f B' | f | f B' f_u | |
|Refer- | ------ | --+----- | ---+--- | -+--+--- | |
| ence. | B' | f_u | B' f_u | | |
| +------+-----+------+------+-------+------+-------+-----+ Total.|
| |Forked| Bar.|Forked|Fused.|Forked.| Bar |Forked |Wild-| |
| |fused.| | bar. | | |fused.|bar |type.| |
| | | | | | | |fused. | | |
+-------+------+-----+------+------+-------+------+-------+-----+-------+
| 163 | 45 | 55 | .. | 1 | 4 | 2 | .. | .. | 108 |
| 164 | 71 | 90 | .. | .. | 4 | 1 | .. | .. | 166 |
| 165 | 97 | 106 | .. | .. | 2 | 4 | .. | .. | 209 |
| 11 | 21 | 35 | .. | .. | 1 | 2 | .. | .. | 59 |
| 33 | 15 | 23 | .. | .. | .. | 1 | .. | .. | 39 |
| +------+-----+------+------+-------+------+-------+-----+-------+
| Total.| 250 | 309 | .. | 1 | 11 | 10 | .. | .. | 581 |
+-------+------+-----+------+------+-------+------+-------+-----+-------+

{60}

The same three points were combined in a different way, namely, by mating forked females to bar fused males. The bar daughters were back-crossed to forked fused males and gave the results shown in table 42.

TABLE 42.--_P_1 forked_ [female] [female] x _bar fused_ [male] [male]. _B.C. F_1 bar_ [female] x _forked fused_ [male] [male].

+------+--------------+-------------+-------------+--------------+------+
| | f | f B' f_u | f f_u | f B' | |
| | ------ | -+------ | --+--- | -+--+-- | |
|Refer-| B' f | | B' | f_u |Total.|
| ence.+-------+------+------+------+------+------+------+-------+ |
| |Forked.| Fused|Forked| Wild-|Forked| Bar. |Forked| Fused.| |
| | | bar. | bar | type.|fused.| |bar. | | |
| | | |fused.| | | | | | |
+------+-------+------+------+------+------+------+------+-------+------+
|158 | 131 | 124 | 1 | .. | 3 | 3 | .. | .. | 262 |
|159 | 31 | 45 | .. | .. | .. | .. | .. | .. | 76 |
|160 | 29 | 23 | .. | .. | 1 | 2 | .. | .. | 55 |
|161 | 24 | 11 | 1 | .. | .. | .. | .. | .. | 36 |
|162 | 96 | 91 | 2 | .. | 1 | 1 | .. | .. | 191 |
| +-------+------+------+------+------+------+------+-------+------+
|Total.| 311 | 294 | 4 | .. | 5 | 6 | .. | .. | 620 |
+------+-------+------+------+------+------+------+------+-------+------+

By combining the results of tables 41 and 42 data are obtained for cross-over values from which (by balancing the inviable classes, as explained in table 43) the element of inviability is reduced to a minimum.

TABLE 43.

+----------+------------+------------+------------+------------+--------+
| | | | | | |
| | ------ | -+---- | ----+- | -+--+- | Total. |
| | | | | | |
+----------+------------+------------+------------+------------+--------+
| | | | | | |
| | 1,164 | 5 | 32 | 0 | 1,201 |
|Per cent. | 96.9 | 0.42 | 2.7 | 0 | |
+----------+------------+------------+------------+------------+--------+

The linkages involved in these data are very strong. The cross-overs between forked and bar number only 5 in a total of 1,201, which gives less than 0.5 per cent of crossing-over. There are 32 cross-overs or 2.7 per cent between bar and fused. The value for forked fused is the sum of the two other values, or 3.1 per cent.

LINKAGE OF SABLE, RUDIMENTARY, AND FORKED.

Rudimentary, forked, bar, and fused form a rather compact group at the right end of the chromosome, as do yellow, lethal 1, white, abnormal, etc., at the zero end. The following two experiments were made to determine more accurately the interval between rudimentary and the other members of this group. A sable rudimentary forked {61} male mated to a wild female gave wild-type sons and daughters. These inbred give the results shown in table 44.

TABLE 44.--_P_{1} sable rudimentary forked_ [male] x _wild_ [female]. _F_{1} wild-type_ [female] x _F_{1} wild-type_ [male] [male].

+----------+---------+-----------------+-------------------+
| | | s r f | s |
| | | ------ | -+---- |
| | | | r f |
| | +-----------+-----+-------+-----------+
|Reference.|Wild-type| Sable |Wild-| Sable.|Rudimentary|
| |[female] |rudimentary|type.| | forked. |
| |[female].| forked. | | | |
+----------+---------+-----------+-----+-------+-----------+
| 264 | 98 | 28 | 17 | 2 | 5 ~
| 265 | 97 | 29 | 54 | 4 | 9 ~
| 266 | 114 | 42 | 49 | 11 | 11 |
+----------+---------+-----------+-----+-------+-----------+
|Total | 309 | 99 |120 | 17 | 25 |
+----------+---------+-----------+-----+-------+-----------+

+----------+--------------------+--------------------+
| | s r | s f |
| | ---+- | -+--+- |
| | f | r |
| +------------+-------+-------+------------+
|Reference.| Sable |Forked.|Sable |Rudimentary.|
| |rudimentary.| |forked.| |
| | | | | |
+----------+------------+-------+-------+------------+
~ 264 | 1 | 1 | .. | .. |
~ 265 | .. | .. | .. | .. |
| 266 | .. | 2 | .. | .. |
+----------+------------+-------+-------+------------+
|Total | 1 | 3 | .. | .. |
+----------+------------+-------+-------+------------+

There were 265 males, of which 42 were cross-overs between sable and rudimentary and 4 between rudimentary and forked. The values found are: sable rudimentary, 16; rudimentary forked, 1.5; sable forked, 17.

LINKAGE OF RUDIMENTARY, FORKED, AND BAR.

The three gens, rudimentary, forked, and bar, form a very compact group. A rudimentary forked male was crossed to bar females and the daughters (bar) were back-crossed singly to rudimentary forked males, the results being shown in table 45.

TABLE 45.--_P_1 rudimentary forked_ [male] x _bar_ [female]. _B.C. F_1 bar_ [female] x _rudimentary forked_ [male] [male].

+----------+---------------+---------------+-------------+--------------+
| | r f | r B' | r f B' | r |
| | ------ | -+---- | ----+- | -+--+- |
| | B' | f | | f B' |
| +---------+-----+-------+-------+-------+-----+-------+------+
|Reference.| Rudim- | Bar.| Rudim-|Forked.| Rudim-|Wild-| Rudim-|Forked|
| | entary | | entary| | entary|type.| entary| bar. |
| | forked. | | bar. | | forked| | | |
| | | | | | bar. | | | |
+----------+---------+-----+-------+-------+-------+-----+-------+------+
|267 | 56 | 104 | .. | 2 | 1 | 1 | .. | .. |
|268 | 82 | 86 | 1 | 2 | .. | .. | .. | .. |
|269 | 68 | 101 | .. | .. | .. | 1 | .. | .. |
+----------+---------+-----+-------+-------+-------+-----+-------+------+
|Total | 206 | 291 | 1 | 4 | 1 | 2 | .. | .. |
+----------+---------+-----+-------+-------+-------+-----+-------+------+

The cross-over values are: rudimentary forked, 1; forked bar, 0.6; rudimentary bar, 1.6. The order of factors is rudimentary, forked, bar. On the basis of the total data the locus of forked is at 56.5. {62}

SHIFTED.

Shifted appeared (January 1913) in a stock culture of vermilion dot. The chief characteristic of this mutant is that the third longitudinal vein (see text-fig. F) does not reach the margin as it does in the normal fly. The vein is displaced toward the fourth throughout its length, and only very rarely does it extend far enough to join the marginal vein. The cross-vein between the third and the fourth veins is often absent because of the shifting. The flies themselves are smaller than normal. The wings are held out from the body at a wide angle. The two posterior bristles of the scutellum are much reduced in size and stick straight up--a useful landmark by which just-hatched shifted flies may be recognized, even though the wings are not expanded.

LINKAGE OF SHIFTED AND VERMILION.

Since shifted arose in vermilion, the double recessive shifted vermilion was available for the following linkage experiment: shifted vermilion males by wild females gave wild-type males and females which inbred gave the data shown in table 46.

Disregarding the eye-color, the following is a summary of the preceding results: wild-type [female], 1,001; wild-type [male], 437; shifted [male], 328. The result shows that shifted is a sex-linked recessive. The data of table 46 show that the locus of shifted lies about 15 units on one side or the other of vermilion, which from the calculated position of vermilion at 33 would give a position for shifted at either 18 or 48 from yellow.

TABLE 46.--_P_1 shifted vermilion [male] [male] x wild [female] [female]. F_1 wild-type [female] x F_1 wild-type [male] [male]._

Key to columns:

A: Wild-type [female] [female].
B: Non-cross-over [male] [male], Shifted.
C: Non-cross-over [male] [male], Wild-type.
D: Cross-over [male] [male], Shifted.
E: Cross-over [male] [male], Wild-type.
F: Total [male] [male].
G: Cross-over values.

+--------------+---------+------+------+-------+-------+-------+------+
| Reference. | A | B | C | D | E | F | G |
+--------------+---------+------+------+-------+-------+-------+------+
| 13 | 345 | 79 | 115 | 8 | 25 | 227 | 15 |
| 29 | 68 | 20 | 32 | 3 | 4 | 59 | 12 |
| 30 | 191 | 37 | 54 | 5 | 13 | 109 | 17 |
| 31 | 151 | 41 | 65 | 17 | 13 | 136 | 22 |
| 33 | 133 | 49 | 40 | 4 | 6 | 99 | 10 |
| 34 | 113 | 56 | 59 | 9 | 11 | 135 | 15 |
+--------------+---------+------+------+-------+-------+-------+------+
| Total. | 1,001 | 282 | 365 | 46 | 72 | 765 | 15 |
+--------------+---------+------+------+-------+-------+-------+------+

{63}

LINKAGE OF SHIFTED, VERMILION, AND BAR.

In order to determine on which side of vermilion shifted lies, a shifted vermilion (not-bar) female was crossed to a (not-shifted red) bar male. Three factors are involved, of which one, bar, is dominant. The shifted vermilion (not-bar) stock is a triple recessive, and a three-point back-cross was therefore possible. The daughters were bar and the sons were shifted vermilion (the triple recessive). Inbred these gave the results shown in table 46. The smallest classes (double cross-overs) are shifted and vermilion bar, which places shifted to the left of vermilion at approximately 17.8 units from yellow.

TABLE 47.--_P_1 shifted vermilion_ [female] x _bar_ [male] [male]. _F_1 bar_ [female] x _F_1 shifted vermillion_ [male] [male].