Chapter VI: Part II: New Data (3)

+-------+---------------+---------------+---------------+---------------+
| | s_h v | s_h B' | s_h v B' | s_h |
| Refer-| ------ | --+---- | -----+- | --+-+-- |
| ence. | B' | v | | v B' |
| +----------+----+--------+------+---------+-----+--------+------+
| |Shifted |Bar.|Shifted |Verm- |Shifted |Wild-|Shifted.| Verm-~
| |vermilion.| | bar. |ilion.|vermilion|type.| | ilion~
| | | | | |bar. | | | bar. |
+-------+----------+----+--------+------+---------+-----+--------+------+
| 65 | 56 |108 | 15 | 20 | 8 | 33 | 1 | 1 |
+-------+----------+----+--------+------+---------+-----+--------+------+

+----------+------+----------------------------+
| | | |
|Reference.|Total.| Cross-over values. |
| | | |
| | +----------+---------+-------+
~ | |Shifted |Vermilion|Shifted|
~ | |vermilion.|bar. |bar. |
| | | | | |
+----------+------+----------+---------+-------+
| 65 | 242 | 15 | 18 | 31 |
+----------+------+----------+---------+-------+

The stock of shifted has been thrown away, since too great difficulty was encountered in maintaining it, because, apparently, of sterility in the females.

LETHALS SA AND SB.

The first lethal found by Miss Rawls was in a stock that had been bred for about 3 years. While there was no _a priori_ reason that could be given to support the view that lethal mutations would occur more frequently among flies inbred in confinement, nevertheless a hundred females from each of several newly caught and from each of several confined stocks were examined for lethals (Stark, 1915). No lethals were found among the wild stocks, but 4 were found among the confined stocks. Whether this difference is significant is perhaps open to question. The first lethal was found in January 1913, in a stock that had been caught at Falmouth, Massachusetts, in 1911, and had been inbred for 18 months, _i.e._, for about 50 generations. This lethal, lethal _sa_, was recessive and behaved like the former lethals, being transmitted by half the females and causing the death of half the sons. The position of this lethal to the X chromosome was found as follows, by means of the cross-over value white lethal _sa_. Lethal-bearing females were mated to white males and the lethal-bearing daughters were again mated to white males. The white sons (894) were non-cross-overs and the red sons (256) were cross-overs. The percentage of crossing-over {64} is 22.2. A correction of 0.4 unit should be added for double crossing-over, indicating that the locus is 22.6 units from white, or at 23.7.

When the work on lethal _sa_ had been continued for 3 months, the second lethal, lethal _sb_, was found (April 1913) to be present in a female which was already heterozygous for lethal _sa_. It is probable that this second lethal arose as a mutation in the father, and that a sperm whose X carried lethal _sb_ fertilized an egg whose X carried lethal _sa_. As in the cases of lethals 1 and 1_a_ and lethals 3 and 3_a_, this lethal, lethal _sb_, was discovered from the fact that only a very few sons were produced, there being 82 daughters and only 3 sons. If, as in the other cases, the number of daughters is taken as the number of non-cross-overs and twice the number of sons as the cross-overs, it is found that the two lethals are about 7 units apart. Since the two lethals were in different X chromosomes, all the daughters should receive one or the other lethal, except in those few cases in which crossing over had taken place. Of the daughters 19 were tested and every one was found to carry a lethal. Again, if the cross-over values of the lethals with some other character, such as white eyes, be found and plotted, the curve should show two modes corresponding to the two lethals. This test was applied, but the curve failed to show two modes clearly,[7] the two lethals being too close together to be differentiated by the small number of determinations that were made. It seems probable that lethal _sa_ and lethal _sb_ are about 5 units apart.

The position of lethal _sb_ was accurately found by continuing the determinations with a white lethal cross-over. A white female was found which had only one of the two lethals and the linkage of this lethal with eosin and miniature was found as follows: A female carrying white and lethal in one chromosome and no mutant factor in the homologous chromosome was bred to an eosin miniature male. The white eosin daughters carried lethal, and their sons show the amount of crossing-over between white and lethal (15.6), between lethal and miniature (19.9), and between white and miniature (32.9). The data on which these calculations are based are given in table 48.

TABLE 48.--_Data on the linkage of white, lethal sb, and miniature, from Stark, 1915_.

+-----------+------------+------------+--------------+
| w^e m | w^e l_{sb} | w^e | w^e l_{sb} m |
| --------- | ---+------ | -------+-- | ---+-----+-- |
| w l_{sb} | w m | w l_{sb} m | w |
| | | | |
+-----------+------------+------------+--------------+
| Eosin | White | Eosin. | White. ~
| miniature | miniature. | | ~
| | | | |
+-----------+------------+------------+--------------+
| 2,421 | 524 | 685 | 48 |
+-----------+------------+------------+--------------+

+--------+--------------------------------+
| | |
| | Cross-over values. |
| | |
| | |
| Total. +----------+----------+----------+
~ |White |Lethal |White |
~ |lethal |_sb_ |miniature.|
| |_sb_. |miniature.| |
+--------+----------+----------+----------+
| 3,678 | 15.6 | 19.9 | 32.9 |
+--------+----------+----------+----------+

{65}

The locus of this lethal is at 16.7; the locus of lethal _sa_ was found to be at 23.7, so that the lethal at 16.7 is evidently the second lethal or lethal _sb_ whose advent gave rise to the high sex-ratio. This interpretation is in accord with the curve which Miss Stark published, for although the mode which corresponds to lethal _sa_ is weak, the mode at 15-16 is well marked.

The two other lethals, lethals _sc_ and _sd_, which came up in the course of these experiments by Miss Stark, are treated in other sections of this paper.

BAR.

(Plate II, figures 12 and 13.)

The dominant sex-linked mutant called bar-eye (formerly called barred) appeared in February 1913 in an experiment involving rudimentary and long-winged flies (Tice, 1914). A female that is heterozygous for bar has an eye that is intermediate between the rounded eye of the wild fly and the narrow band of the bar stock. This heterozygous bar female is always readily distinguishable from the normal, but can not always be separated from the pure bar. Bar is therefore nearly always used as a dominant and back-crosses are made with normal males.

Bar is the most useful sex-linked character so far discovered, on account of its dominance, the certainty of its classification, and its position near the right end of the X chromosome. The locus of bar at 57 was determined on the basis of the data of table 65.

NOTCH.

A sex-linked dominant factor that brings about a notch at the ends of the wings appeared in March 1913, and has been described and figured by Dexter (1914, p. 753, and fig. 13, p. 730). The factor acts as a lethal for the male. Consequently a female heterozygous for notch bred to a wild male gives a 2:1 sex-ratio; half of her daughters are notch and half normal; the sons are only normal. The actual figures obtained by Dexter were 235 notch females, 270 normal females, and 235 normal males.

The location of notch in the X chromosome was not determined by Dexter, but the mutant has appeared anew three or four times and the position has been found by Bridges to be approximately at 2.6. {66}

DEPRESSED.

Several mutations have appeared in which the wings are not flat. Of these the first that appeared was curved (second chromosome), in which the wings are curved downward throughout their length, but are elevated and held out sidewise from the body; the texture is thinner than normal. The second of these wing mutants to appear was jaunty (second chromosome), in which the wings turn up sharply at the tip; they lie in the normal position. The third mutant, arc (second chromosome), has, as its name implies, its wings curved like the arc of a circle. The fourth mutant, bow (first chromosome, fig. C), is like arc, but the amount of curvature is slightly less. The fifth mutant, depressed (first chromosome, fig. G), has the tip of its wings turned down instead of up, as in jaunty, but, as in jaunty, the wing is straight, except near the tip, where it bends suddenly. These stocks have been kept separate since their origin, and flies from them have seldom been crossed to each other, because in the succeeding generations it would be almost impossible to make a satisfactory classification of the various types. But that they are genetically different mutations is at once shown on crossing any two, when wild-type offspring are produced. For instance, bow and arc are the two most nearly alike. Mated together (bow [male] by arc [female]), they give in F_1 straight-winged flies which inbred give in F_2 9 straight to 7 not-straight (_i.e._, bow, arc, and bow arc together).

Depressed wings first appeared (April 1913) among the males of a culture of black flies. They were mated to their sisters and from subsequent generations both males and females with depressed wings were obtained which gave a pure stock. This new character proved to be another sex-linked recessive.

LINKAGE OF DEPRESSED AND BAR.

Depressed (not-bar) males mated to (not-depressed) bar females gave bar daughters. Two of these were back-crossed singly to depressed males and gave the results shown in table 49. Males and females were not separated, since they should give the same result.

TABLE 49.--_P_1 depressed_ [female] [female] x _bar_ [female] [female]. _B.C. F_1 bar_ [female] x _depressed_ [male] [male].

+----------+--------------------+-------------------+-------+-----------+
| | Non-cross-overs. | Cross-overs. | | |
+----------+-------------+------+-----------+-------+ | |
|Reference.| Depressed. | Bar. | Depressed | Wild- | Total.| Cross-over|
| | | | bar. | type. | | values. |
+----------+-------------+------+-----------+-------+-------+-----------+
| 66 I | 48 | 51 | 21 | 41 | 161 | 39 |
| 67 I | 85 | 104 | 44 | 70 | 303 | 38 |
+----------+-------------+------+-----------+-------+-------+-----------+
| Total.| 133 | 155 | 65 | 111 | 464 | 38 |
+----------+-------------+------+-----------+-------+-------+-----------+

{67}

LINKAGE OF CHERRY, DEPRESSED, AND VERMILION.

The linkage value 38 (see table 49) indicates that depressed is somewhere near the opposite end of the series of sex-linked factors from bar. The locus could be more accurately determined by finding the linkage relations of depressed with gens at its end of the chromosome. Accordingly, depressed females were crossed to cherry vermilion males. F_1 gave wild-type females and depressed males. The daughters bred again to cherry vermilion males gave the results shown in table 50. The data only suffice to show that the locus of depressed is about midway between cherry and vermilion, or at about 15 units from yellow.

The F_1 males in the last experiment did not have their wings as much depressed as is the condition in stock males, and in F_2 most of the depressed winged males were of the F_1 type, although a few were like those of stock. This result suggests that the stock is a double recessive, _i. e._, one that contains, in addition to the sex-linked depressed, an autosomal factor that intensifies the effect of the primary sex-linked factor.

TABLE 50.--_P_1 depressed [female] x cherry vermilion [male] [male]._

+-------------------++---------------------------------------+
| || Second generation. |
| First |+----------+--------+-------------------+
| generation. || | | w^c v |
+---------|---------+| | | ------- |
| | || | | d_p |
| Wild- |Depressed|| | +---------+---------+
| type | [male] ||Reference.| | | ~
|[female] | [male]. || |[female]|Cherry | ~
|[female].| || |[female]|vermilion|Depressed|
| | || | | | |
| | || | | [male]. | [male]. |
+---------+---------++----------+--------+---------+---------+
| 21 | 31 || 19 I | 59 | 23 | 24 |
+---------+---------++----------+--------+---------+---------+

+---------------------------------------------------------+
| Second generation. |
+-------------------+-------------------------------------+
| w^c d_p | w^c | w^c d_p v |
| --+----- | -----+-- | --+----+--- |
| v | d_p v | |
+---------+---------+--------+---------+---------+--------|
~ | | | | | |
~ Cherry | | Cherry |Depressed|Cherry | Wild- |
|depressed|Vermilion| |vermilion|depressed| type |
| | | | |vermilion| |
| [male]. |[male]. |[male]. | [male]. | [male]. | [male].|
+---------+---------+--------+---------+---------+--------+
| 6 | 6 | 5 | 5 | 0 | 0 |
+---------+---------+--------+---------+---------+--------+

{68}

CLUB.

In May 1913 there were observed in a certain stock some flies which, although mature, did not unfold their wings (text-fig. H_a_). This condition was at first found only in males and suspicion was aroused that the character might be sex-linked. When these males were bred to wild females the club-shaped wings reappeared only in the F_2 males, but in smaller number than expected for a recessive sex-linked character. The result led to the further suspicion that not all those individuals that are genetically club show club somatically. These points are best illustrated and proven by the following history of the stock:

Club females were obtained by breeding F_2 club males to their F_2 long-winged sisters, half of which should be heterozygous for club. {69} 5,352; wild-type [male], 4,181; club [male], 236. The wild-type males include, of course, those club males that have expanded wings (potential clubs).

Club females by wild males gave in the F_2 generation (mass cultures): wild-type [female], 1,131; wild-type [male], 897; club [female], 57; club [male], 131.

It is noticeable that there were fewer club females than club males, equality being expected, which might appear to indicate that the club condition is more often realized by the male than by the female, but later crosses show that the difference here is not a constant feature of the cross.

Long-winged males from club stock (potential clubs) bred to wild females gave in F_2 the following: wild-type [female], 521; wild-type (and potential club) [male], 403; club [male], 82.

Club females by club males of club stock gave in F_2: potential club [female], 126; potential club [male], 78; club [female], 95; club [male], 81. These results are from 8 pairs. The high proportion of club is noticeable.

Potential club females and males from pure club stock (_i. e._, stock derived originally from a pair of club) gave in F_2 the following: potential club [female], 1,049; potential club [male], 666; club [female], 450; club [male], 453.

GENOTYPIC CLUB.

Accurate work with the club character was made possible by the discovery of a character that is a constant index of the presence of homozygous club. This character is the absence of the two large bristles (text-fig. H_c_) that are present on each side of the thorax of the wild fly as shown in figure Hb. All club flies are now classified by this character and no attention is paid to whether the wings remain as pads or become expanded.

LINKAGE OF CLUB AND VERMILION.

The linkage of club and vermilion is shown by the cultures listed in table 51, which were obtained as controls in working with lethal III. The cross-over value is shown in the male classes by the cross-over fraction 276/1463 or 19 per cent.

LINKAGE OF YELLOW, CLUB, AND VERMILION.

The data just given in table 51 show that club is 19 units from vermilion, but in order to determine in which direction from vermilion it lies, the crossing-over of club to one other gen must be tested. For this test we used yellow, which lies at the extreme left of the chromosome series. At the same time we included vermilion, so that a three-point experiment was made.

Females that were (gray) club vermilion were bred to yellow (not-club red) and gave wild-type daughters and club vermilion sons. These inbred gave the results of table 52.

The data from the males show that the locus of club is about midway between yellow and vermilion. This conclusion is based on the {70} evidence that yellow and club give 18 per cent of crossing-over, club and vermilion 20 per cent, and yellow and vermilion 35 per cent. The double cross-overs on this view are yellow club (3) and vermilion (3). The females furnish additional data for the linkage of club and vermilion. The value calculated from the female classes alone is 20 units, which is the same value as that given by the males.

TABLE 51.--_P_1 club_ [female] [female] x _vermilion_ [male] [male]. _F_1 wild-type_ [female] x _F_1 club_ [male].

+----------+--------+-----------------+-----------------+-------+-------+
| | | Non-cross-over | Cross-over | | |
| | | [male] [male]. | [male] [male]. | | |
| | +------+----------+----------+------+ Total |Cross- |
|Reference.|Females.| Club.|Vermilion.|Club |Wild- |[male] | over |
| | | | |Vermilion.|type. |[male].|values.|
| | | | | | | | |
+----------+--------+------+----------+----------+------+-------+-------+
| 137 | 75 | 17 | 39 | 6 | 11 | 73 | 23 |
| 138 | 64 | 24 | 32 | 6 | 8 | 70 | 20 |
| 139 | 56 | 10 | 31 | 4 | 3 | 48 | 15 |
| 140 | 74 | 13 | 39 | 3 | 5 | 60 | 13 |
| 144 | 97 | 30 | 40 | 10 | 13 | 93 | 25 |
| 145 | 63 | 15 | 29 | 4 | 6 | 54 | 19 |
| 146 | 126 | 44 | 46 | 9 | 9 | 108 | 15 |
| 106 | 92 | 33 | 34 | 6 | 10 | 83 | 19 |
| 107 | 55 | 31 | 25 | 7 | 3 | 66 | 15 |
| 108 | 86 | 29 | 32 | 7 | 10 | 78 | 22 |
| 109 | 103 | 25 | 36 | 4 | 9 | 74 | 18 |
| | 83 | 30 | 34 | 6 | 9 | 79 | 19 |
| | 77 | 18 | 26 | 7 | 8 | 59 | 25 |
| | 67 | 20 | 21 | 6 | 7 | 54 | 24 |
| | 126 | 32 | 60 | 15 | 13 | 120 | 23 |
| | 63 | 21 | 28 | 7 | 10 | 66 | 26 |
| | 114 | 45 | 71 | 9 | 7 | 132 | 12 |
| | 46 | 18 | 18 | 3 | 3 | 42 | 14 |
| | 111 | 35 | 56 | 6 | 7 | 104 | 13 |
| +--------+------+----------+----------+------+-------+-------+
| Total.| 1,578 | 490 | 697 | 125 | 151 | 1,463 | 19 |
+----------+--------+------+----------+----------+------+-------+-------+

TABLE 52.--_P_1 club vermilion_ [female] [female] x _yellow_ [male] [male]. _F_1 wild-type_ [female] [female] x _F_1 club vermilion_ [male] [male].

+------------+-----------------------------------+
| | F_2 females. |
| +-----------------+-----------------+
| | Non-cross-overs.| Cross-overs. |
| | | |
| | | |
|Reference. +-----------+-----+------+----------+
| | Club |Wild-| Club.|Vermilion.~
| | vermilion.|type.| | ~
+------------+-----------+-----+------+----------+
| 99 | 44 | 52 | 13 | 7 |
| 100 | 38 | 58 | 6 | 12 |
| 101 | 30 | 32 | 6 | 12 |
| 102 | 44 | 55 | 20 | 13 |
| 103 | ... |... | ... | ... |
| +-----------+-----+------+----------+
| Total. | 156 |197 | 45 | 44 |
+------------+-----------+-----+------+----------+

+-----------------------------------------------------------------------+
| F_2 males. |
+------------------+-----------------+----------------+-----------------+
| y | y c_l v | y v | y c_l |
| ------ | -+----- | ---+- | -+--+- |
| c_l v | | c_l | v |
+-------+----------+-----------+-----+----------+-----+------+----------+
~Yellow.|Club |Yellow club|Wild-|Yellow |Club.|Yellow|Vermilion.|
~ |vermilion.|vermilion. |type.|vermilion.| |club. | |
+-------+----------+-----------+-----+----------+-----+------+----------+
| 35 | 27 | 2 | 9 | 8 | 11 | 0 | 1 |
| 43 | 23 | 1 | 15 | 11 | 14 | 0 | 0 |
| 19 | 24 | 6 | 5 | 10 | 3 | 1 | 0 |
| 48 | 38 | 12 | 14 | 8 | 15 | 1 | 1 |
| 43 | 32 | 7 | 16 | 13 | 7 | 1 | 1 |
+-------+----------+-----------+-----+----------+-----+------+----------+
| 188 | 144 | 28 | 59 | 50 | 50 | 3 | 3 |
+-------+----------+-----------+-----+----------+-----+------+----------+

{71}

LINKAGE OF CHERRY, CLUB, AND VERMILION.

The need for a readily workable character whose gen should lie in the long space between cherry and vermilion has long been felt. Cherry and vermilion are so far apart that there must be considerable double crossing-over between them. But with no favorably placed character which is at the same time viable and clearly and rapidly distinguishable, we were unable to find the exact amount of double crossing-over, and hence could not make a proper correction in plotting the chromosome. Club occupies just this favorable position nearly midway between cherry and vermilion. The distances from cherry to club and from club to vermilion are short enough so that no error would be introduced if we ignored the small amount of double crossing-over within each of these distances.

It thus becomes important to know very exactly the cross-over values for cherry club and club vermilion. The experiment has the form of the yellow club vermilion cross of table 52, except that cherry is used instead of yellow. Cherry is better than yellow because it is slightly nearer club than is yellow and because the bristles of yellow flies are very inconspicuous. In yellow flies the bristles on the side of the thorax are yellowish brown against a yellow background, while in gray-bodied flies the bristles are very black against a light yellowish-gray background.

For the time being we are able to present only incomplete results upon this cross. In the first experiment cherry females were crossed to club vermilion males and the wild-type daughters were back-crossed to cherry club vermilion, which triple recessive had been secured for this purpose. Table 53 gives the results.

TABLE 53.--_P_{1} cherry_ [female] [female] x _club vermilion_ [male] [male]. _B. C. F__{1} _wild-type_ [female] x _cherry club vermilion_ [male] [male].

+--------+-------------------+-------------------+-------------------+
| | w^c | w^c c_l v | w^c v |
| | --------------- | ----+---------- | -----------+--- |
| Refer- | c_l v | | c_l |
| ence. +-------------------+---------+---------+-------------------+
| | | | | | | |
| | | Club | Cherry | | Cherry | |
| | Cherry. | ver- | club | Wild- | ver- | Club. |
| | | milion. | ver- | type. | milion. | |
| | | | milion. | | | |
+--------+---------+---------+---------+---------+---------+---------+
| | | | | | | ~
| 163 | 68 | 68 | 4 | 10 | 21 | 13 ~
| 164 | 99 | 67 | 13 | 21 | 21 | 12 |
| 165 | 23 | 37 | 9 | 7 | 15 | 2 |
| 166 | 107 | 86 | 14 | 28 | 31 | 43 |
| 167 | 42 | 49 | 7 | 11 | 12 | 11 |
| 168 | 40 | 30 | 6 | 15 | 16 | 8 |
| +---------+---------+---------+---------+---------+---------+
| Total. | 379 | 337 | 53 | 92 | 116 | 89 |
+--------+---------+---------+---------+---------+---------+---------+

+-------------------+---------+----------------------------+
| w^c c_l | | |
| ----+------+--- | | Cross-over values. |
| v | | |
+---------+---------+ +----------------------------+
| | | | | | |
| | | Total. | | Club. | Cherry |
| Cherry | Ver- | | Cherry | ver- | ver- |
| club. | milion. | | club. | milion. | milion. |
| | | | | | |
+---------+---------+---------+--------+---------+---------+
~ | | | | | |
~ 1 | 0 | 185 | 8 | 19 | 26 |
| 1 | 0 | 234 | 15 | 15 | 29 |
| 0 | 2 | 95 | 19 | 25 | 35 |
| 3 | 3 | 315 | 15 | 25 | 37 |
| 2 | 2 | 136 | 16 | 20 | 30 |
| 0 | 0 | 115 | 18 | 21 | 39 |
+---------+---------+---------+--------+---------+---------+
| 7 | 7 | 1,080 | 15 | 20 | 32 |
+---------+---------+---------+--------+---------+---------+

{72}

A complementary experiment was made by crossing cherry club vermilion females to wild males and inbreeding the F_1 in pairs. Table 54 gives the results of this cross.

TABLE 54.--_P_{1} cherry club vermilion_ [male] [male]. [female] [female] x _wild_ [male] [male]. _F_{1} wild-type_ [female] x _F_{1} cherry club vermilion_ [male] [male].

+----------+-----------------+------------------+-----------------+
| | w^c c_l v | w^c | w^c c_l |
| | ------------- | ----+-------- | ---------+--- |
| | | c_l v | v |
| +-----------+-----+-------+----------+------+----------+
|Reference.|Cherry club|Wild-|Cherry.| Club |Cherry|Vermilion.|
| |vermilion. |type.| |vermilion.| club.| |
+----------+-----------+-----+-------+----------+------+----------+
| 188 | 60 | 76 | 12 | 8 | 12 | 29 ~
| 189 | 228 | 314 | 48 | 44 | 50 | 60 ~
| 197 | 68 | 81 | 23 | 13 | 9 | 22 |
+----------+-----------+-----+-------+----------+------+----------+
|Total. | 356 | 471 | 83 | 65 | 71 | 111 |
+----------+-----------+-----+-------+----------+------+----------+

+----------------+------+----------------------------+
| w^c v | | |
| ----+----+--- | | Cross-over values. |
| c_l | | |
+----------+-----+Total.+------+----------+----------+
| Cherry |Club.| |Cherry|Club |Cherry |
|vermilion.| | |club. |vermilion.|vermilion.|
+----------+-----+------+------+----------+----------+
~ 2 | 1 | 200 | 11 | 22 | 30 |
~ 1 | 8 | 753 | 13 | 16 | 27 |
| 2 | 0 | 218 | 17 | 15 | 31 |
+----------+-----+------+------+----------+----------+
| 5 | 9 |1,171 | 14 | 17 | 28 |
+----------+-----+------+------+----------+----------+

The combined data of tables 53 and 54 give 14.2 as the value for cherry club. All the data thus far presented upon club vermilion (886 cross-overs in a total of 4,681), give 19.2 as the value for club vermilion. The locus of club on the basis of the total data available is at 14.6.

GREEN.

In May 1913 there appeared in a culture of flies with gray body-color a few males with a greenish-black tinge to the body and legs. The trident pattern on the thorax, which is almost invisible in many wild flies, was here quite marked. A green male was mated to wild females and gave in F_2 a close approach to a 2:1:1 ratio. The green reappeared only in the F_2 males, but the separation of green from gray was not as easy or complete as desirable. From subsequent generations a pure stock of green was made. A green female by wild male gave 138 wild-type females and 127 males which were greenish. This green color varies somewhat in depth, so that some of these F_1 males could not have been separated with certainty from a mixed culture of green and gray males.

The results of these two experiments show that green is a sex-linked melanistic character like sable, but the somatic difference produced is much less than in the case of sable, so that the new mutation, although genetically definite, is of little practical value. We have found several eye-colors which differed from the red color of the wild fly by very small differences. With some of these we have worked successfully by using another eye-color as a developer. For example, the double recessive vermilion "clear" is far more easily distinguished from vermilion than is clear from red. But it is no small task to make up the stocks {73} necessary for such a special study. In the case of green we might perhaps have employed a similar method, performing all experiments with a common difference from the gray in all flies used.

CHROME.

In a stock of forked fused there appeared, September 15, 1913, three males of a brownish-yellow body-color. They were uniform in color, without any of the abdominal banding so striking in other body-colors. Even the tip of the abdomen lacked the heavy pigmentation which is a marked secondary sexual character of the male. About 20 or more of these males appeared in the same culture. This appearance of many males showing a mutant character and the non-appearance of corresponding females is usual for sex-linked characters. In such cases females appear in the next generation, as they did in this case when the chrome males were mated to their sisters in mass cultures. Since both females and males of chrome were on hand, it should have been an easy matter to continue the stock, but many matings failed, and it was necessary to resort to breeding in heterozygous form. The chrome, however, gradually disappeared from the stock. Such a difficult sex-linked mutation as this could be successfully handled (like a lethal) if it could be mated to a double recessive whose members lie one on each side of the mutant, but in the case of chrome this was not attempted soon enough to save the stock.

LETHAL 3.

In the repetition of a cross between a white miniature male and a vermilion pink male (December 1913), the F_2 ratios among the males were seen to be very much distorted because of the partial absence of certain classes (Morgan 1914_c_). While it was suspected that the disturbance was due to a lethal, the data were useless for determining the position of such a lethal, from the fact that more than one mother had been used in each culture. From an F_2 culture that gave practically a 2:1 sex-ratio, vermilion females were bred to club males. Several such females gave sex-ratios. Their daughters were again mated to vermilion males. Half of these daughters gave high female sex-ratios and showed the linkage relations given in table 55.

TABLE 55.--_Linkage data on club, lethal 3, and vermilion, from Morgan, 1914c_.

+----------+-----------------------------------------------------------+
| | Males. |
| +-----------+--------------+------------------+-------------+
| | c_1 | c_1 l_3 v | c_1 v | c_1 l_3 |
| Females. | ------- | --+------ | ----+- | --+--+-- |
| | l_3 v | | l_3 | v |
| +-----------+--------------+------------------+-------------+
| | Club. | Wild-type. | Club vermilion. | Vermilion. |
+----------+-----------+--------------+------------------+-------------+
| 588 | 182 | 28 | 11 | 1 |
+----------+-----------+--------------+------------------+-------------+

{74}

Lethal 3 proved to lie between club and vermilion, 13 units from club and 5 from vermilion. The same locus was indicated by the data from the cross of vermilion lethal-bearing females by eosin miniature males. The complete data bearing on the position of lethal 3 is summarized in table 56. On the basis of this data lethal 3 is located at 26.5.

TABLE 56.--_Summary of linkage data on lethal 3, from Morgan, 1914c_.

+---------------------+--------+--------+------------+
| Gens. | Total. | Cross- | Cross-over |
| | | overs. | values. |
+---------------------+--------+--------+------------+
| Eosin lethal 3 | 1,327 | 268 | 20.2 |
| Eosin vermilion | 1,327 | 357 | 27.0 |
| Eosin miniature | 3,374 | 967 | 29.0 |
| Club lethal 3 | 222 | 29 | 13.0 |
| Club vermilion | 877 | 161 | 18.4 |
| Lethal 3 vermilion | 1,549 | 105 | 6.8 |
| Lethal 3 miniature | 1,481 | 138 | 9.3 |
| Vermilion miniature | 1,327 | 31 | 2.3 |
+---------------------+--------+--------+------------+

LETHAL 3a.

In January 1914 a vermilion female from a lethal 3 culture when bred to a vermilion male gave 71 daughters and only 3 sons; 34 of these daughters were tested, and every one of them gave a 2:1 sex-ratio. The explanation advanced (Morgan 1914_c_) was that the mother of the high ratio was heterozygous for lethal 3, and also for another lethal that had arisen by mutation in the X chromosome brought in by the sperm. On this interpretation the few males that survived were those that had arisen through crossing-over. The rarity of the sons shows that the two lethals were in loci near together, although here of course in different chromosomes, except when one of them crossed over to the other. As explained in the section on lethal 1 and 1_a_ the distance between the two lethals can be found by taking twice the number of the surviving males (2+3) as the cross-overs and the number of the females as the non-cross-overs. But the 34 daughters tested were also non-cross-overs, since none of them failed to carry a lethal. The fractions (6+0)/(71+34) = 6/105 give 5.7 as the distance between the lethals in question. In the case of lethals 3 and 3_a_ another test was applied which showed graphically that two lethals were present. Each of the daughters tested showed, by the classes of her sons, the amount of crossing-over between white and that lethal of the two that she carried. These cross-over values were plotted and gave a bimodal curve with modes 7 units apart. It had already been shown that the locus of one of the two lethals was at 26.5, and since the higher of the two modes was at about 23, it corresponds to lethal 3. The data and the curve show that the lethals 3 and 3_a_ are about 7 units apart, _i. e._, lethal 3_a_ lies at about 19.5. {75}

LETHAL 1b.

A cross between yellow white males and abnormal abdomen females gave (February 1914) regular results in 10 F_2 cultures, but three cultures gave 2 [female] : 1 [male] sex-ratios (Morgan, 1914_b_, p. 92). The yellow white class, which was a non-cross-over class in these 10 cultures, had disappeared in the 3 cultures. Subsequent work gave the data summarized in table 57. At the time when the results of table 57 were obtained it did not seem possible that two different lethals could be present in the space of about 1 unit between yellow and white, and this lethal was thought to be a reappearance of lethal 1 (Morgan, 1912_b_, p. 92). Since then a large number of lethals have arisen, one of them less than 0.1 unit from yellow, and at least one other mutation has taken place between yellow and white, so that the supposition is now rather that the lethal in question was not lethal 1. Indeed, the linkage data show that this lethal, which may be called lethal 1_b_, lies extraordinarily close to white, for the distance from yellow was 0.8 unit and of white from yellow on the basis of the same data 0.8. There was also a total absence of cross-overs between lethal 1_b_ and white in the total of 846 flies which could have shown such crossing-over. On the basis of this linkage data alone we should be obliged to locate lethal 1_b_ at the point at which white itself is situated, namely, 1.1, but on _a priori_ grounds it seems improbable that a lethal mutation has occurred at the same locus as the factor for white eye-color. Farther evidence against this supposition is that females that have one X chromosome with both yellow and white and the other X chromosome with yellow, lethal, and white are exactly like regular stock yellow white flies. The lethal must have appeared in a chromosome which was already carrying white and yet did not affect the character of the white. We prefer, therefore, to locate lethal 1_b_ at 1.1-.

TABLE 57.--_Summary of all linkage data upon lethal 1b, from Morgan, 1914b_.

+-------------------------+---------+--------+---------------+
| Gens. | Total. | Cross- | Cross-over |
| | | overs. | values. |
+-------------------------+---------+--------+---------------+
| Yellow lethal 1_b_ | 744 | 6 | 0.81 |
| Yellow white | 2,787 | 23 | 0.82 |
| Lethal 1_b_ white | 846 | 0 | 0.0 |
+-------------------------+---------+--------+---------------+

FACET.

Several autosomal mutations had been found in which the facets of the compound eye are disarranged. One that was sex-linked appeared in February 1914. Under the low power of the binocular microscope the facets are seen to be irregular in arrangement, instead of being arranged in a strictly regular pattern. The ommatidia are more nearly circular than hexagonal in outline, and are variable in size, some being considerably larger than normal. The large ones are also darker than {76} the smaller, giving a blotched appearance to the eye. The short hairs between the facets point in all directions instead of radially, as in the normal eye. The irregular reflection breaks up the dark fleck which is characteristic of the normal eye. The shape of the eye differs somewhat from the normal; it is more convex, smaller, and is encircled by a narrow rim destitute of ommatidia.

Facet arose in a back-cross to test the independence of speck (second chromosome) and maroon (third chromosome). One of the cultures produced, among the first males to hatch, some males which showed the facet disarrangement. None of the females showed this character. The complete output was that typical of a female heterozygous for a recessive sex-linked character: not-facet [female] [female] (2), 112; not-facet [male] [male] (1), 57; facet [male] [male] (1), 51.

Of the three characters which were shown by the F_2 males, one, facet, is sex-linked, another, speck, is in the second chromosome, and maroon is in the third chromosome. All eight F_2 classes are therefore expected to be equal in size, and each pair of characters should show free assortment, that is, 50 per cent. The assortment value for facet speck is 48, for speck maroon 52, and for facet maroon 48, as calculated from the F_2 males of table 58.

TABLE 58.--_P_1 speck maroon_ [male] x _wild_ [female] [female]. _B.C. F_1 wild-type_ [female] x _speck maroon_ [male].

+----------+----------------------------+
| | F_2 females. |
|Reference.+-------+-----+------+-------+
| |Speck |Wild-|Speck.|Maroon.|
| |maroon.|type.| | ~
| | | | | ~
+----------+-------+-----+------+-------+
| 66 | 31 | 30 | 26 | 25 |
+----------+-------+-----+------+-------+

+----------------------------------------------------------+
| F_2 males. |
+------+-------+-------+-----+-------+------+------+-------+
|Facet.|Speck |Facet |Wild-|Facet |Speck.|Facet |Maroon.|
~ |maroon.|speck |type.|maroon.| |speck.| |
~ | |maroon.| | | | | |
+------+-------+-------+-----+-------+------+------+-------+
| 14 | 14 | 14 | 10 | 11 | 17 | 12 | 17 |
+------+-------+-------+-----+-------+------+------+-------+

LINKAGE OF FACET, VERMILION AND SABLE.

In order to determine the location of facet in the first chromosome, one of the facet males which appeared in culture 66 was crossed out to vermilion sable females. Three of the wild-type daughters were back-crossed to vermilion sable males. The females of the next generation should give data upon the linkage of vermilion and sable, while the males should show the linkage of all three gens, facet, vermilion, and sable. The offspring of these three females are classified in table 59.

The cross-over fraction for vermilion sable as calculated from the females is 19/194. The cross-over value corresponding to this fraction is 10 units, which was the value found in the more extensive experiments given in the section on sable.

It will be noticed that the results in the males of culture 150 are markedly different from those of the other two pairs. While the sable males are fully represented, their opposite classes, the gray males, are {77} entirely absent. This result is due to a lethal factor, lethal 5, which appeared in this culture for the first time.

The males of the two cultures 149 and 151 give the order of gens as facet, vermilion, sable; that is, facet lies to the left of vermilion and toward yellow. The cross-over values are: facet vermilion 40; vermilion sable 12; facet sable 42. Since yellow and vermilion usually give but 34 per cent of crossing-over, this large value of 40 for facet vermilion shows that facet must lie very near to yellow.

TABLE 59.--_P_1 facet_ [male] x _vermilion sable_ [female] [female]. _B.C. F_1 wild-type_ [female] x _vermilion sable_ [male] [male].

+----------+----------------------------------+
| | F_2 females. |
| +----------------+-----------------+
| | | |
| |Non-cross-overs.| Cross-overs. |
| | | |
|Reference.+---------+------+----------+------+
| |Vermilion|Wild- |Vermilion.|Sable.|
| |sable. |type. | | ~
| | | | | ~
+----------+---------+------+----------+------+
| 149 | 16 | 29 | 3 | 3 |
| 150 | 13 | 17 | 2 | 2 |
| 151 | 37 | 63 | 7 | 2 |
| +---------+------+----------+------+
| Total. | 66 | 109 | 12 | 8 |
+----------+---------+------+----------+------+

+--------------------------------------------------------------------+
| F_2 males. |
+----------------+---------------+-----------------+-----------------+
| f_a | f_a v s | f_a s | f_a v |
| ------ | --+---- | ----+- | --+--+-- |
| v s | | v | s |
+------+---------+---------+-----+------+----------+----------+------+
|Facet.|Vermilion|Facet |Wild-|Facet |Vermilion.|Facet |Sable.|
~ |sable. |vermilion|type.|sable.| |vermilion.| |
~ | |sable. | | | | | |
+------+---------+---------+-----+------+----------+----------+------+
| 17 | 10 | 8 | 12 | 2 | .. | 2 | 1 |
| .. | 10 | 9 | .. | 1 | .. | .. | .. |
| 38 | 23 | 12 | 26 | 2 | 8 | 4 | 1 |
+------+---------+---------+-----+------+----------+----------+------+
| 55 | 43 | 29 | 38 | 5 | 8 | 6 | 2 |
+------+---------+---------+-----+------+----------+----------+------+

LINKAGE OF EOSIN, FACET, AND VERMILION.

In order to obtain more accurate information on the location of facet, a facet male was mated to an eosin vermilion female. The F_1 females were mated singly to wild males and they gave the results shown in table 60. The F_2 females were not counted, since they do not furnish any information. The evidence of table 60 places facet at 1.1 units to the right of eosin, or at 2.2.

TABLE 60.--_P_1 eosin vermilion_ [female] x _facet_ [male]. _F_1 wild-type_ [female] x _wild_ [male].

+----------+-----------------+-----------------+-----------------+
| | w^c v | w^c f_a | w^c |
| | ------- | --+---- | ----+- |
| | f_a | v | f_a v |
|Reference.+----------+------+------+----------+------+----------+
| |Eosin |Facet.|Eosin |Vermilion.|Eosin.|Facet |
| |vermilion.| |facet.| | |vermilion.|
| | | | | | | |
+----------+----------+------+------+----------+------+----------+
| 512 | 43 | 43 | .. | 1 | 13 | 16 ~
| 513 | 28 | 35 | .. | 2 | 19 | 5 ~
| 514 | 18 | 31 | 1 | .. | 17 | 11 |
| 515 | 18 | 60 | .. | .. | 20 | 15 |
| 516 | 10 | 31 | .. | .. | 7 | 12 |
| 517 | 24 | 34 | .. | .. | 10 | 12 |
| 518 | 44 | 38 | 1 | 1 | 23 | 22 |
+----------+----------+------+------+----------+------+----------+
| Total.| 185 | 272 | 2 | 4 | 109 | 93 |
+----------+----------+------+------+----------+------+----------+

+----------------+------+----------------------------+
| w^c f_a v | | |
| --+---+-- | | Cross-over values. |
| | | |
+----------+-----+Total.+------+----------+----------+
|Eosin |Wild-| |Eosin |Facet |Eosin |
|facet |type.| |facet.|vermilion.|vermilion.|
|vermilion.| | | | | |
+----------+-----+------+------+----------+----------+
~ .. | .. | 116 | .... | .... | .... |
~ .. | .. | 89 | .... | .... | .... |
| .. | .. | 78 | .... | .... | .... |
| .. | .. | 113 | .... | .... | .... |
| .. | .. | 60 | .... | .... | .... |
| .. | .. | 80 | .... | .... | .... |
| .. | 1 | 130 | .... | .... | .... |
+----------+-----+------+------+----------+----------+
| .. | 1 | 666 | 1.05 | 30.5 | 31.3 |
+----------+-----+------+------+----------+----------+

{78}

LETHAL SC.

The third of the lethals which Miss Stark found (Stark, 1915) while she was testing the relative frequency of occurrence of lethals in fresh and inbred wild stocks arose in April 1914 in stock caught in 1910. Females heterozygous for this lethal, lethal _sc_, were mated to white males and the daughters were back-crossed to white males. Half of the daughters gave lethal sex-ratio, and these gave 1,405 cross-overs in a total of 3,053 males, from which the amount of crossing-over between white and lethal _sc_ has been calculated as 46 per cent.

By reference to table 65 it is seen that white and bar normally give only about 44 per cent of crossing-over in a two-locus experiment; lethal _sc_ then is expected to be situated at least as far to the right as bar. Females heterozygous for lethal _sc_ were therefore crossed to bar males, and their daughters were tested. The lethal-bearing daughters gave 144 cross-overs in a total of 1,734 males, that is, bar and lethal _sc_ gave 8.3 per cent of crossing-over. Lethal _sc_ therefore lies 8.3 units beyond bar or at about 66.5. The cross-over value sable lethal _sc_ was found to be 23.5 (387 cross-overs in a total of 1,641 males) which places the lethal at 43+23.5, or at 66.5. We know from other data that there is enough double crossing-over in the distance which gives an experimental value of 23.5 per cent, so that the true distance is a half unit longer or the locus at 67.0 is indicated by the 1,641 males of the sable lethal experiment. In a distance so short that the experimental value is only 8.3 per cent there is, as far as we have been able to determine, no double crossing-over at all, or at most an amount that is entirely negligible, so that a locus at 57+8.3 or 65.3 is indicated by the 1,734 males of the bar lethal experiment. To get the value indicated by the total data the cases may be weighted, that is, the value 65.3 may be multiplied by 1,734, and 67.0 may be multiplied by 1,641. The sum of these two numbers divided by the sum of 1,734 and 1,641 gives 66.2 as the locus indicated by all the data available. This method has been used in every case where more than one experiment furnishes data upon the location of a factor. In constructing the map given in diagram I rather complex balancings were necessary.

LETHAL SD.

The fourth lethal which Miss Stark found (May 1914) in the inbred stocks of _Drosophila_ has not been located by means of linkage experiments. It is interesting in that the males which receive the lethal factor sometimes live long enough to hatch. These males are extremely feeble and never live more than two days. There is, as far as can be seen, no anatomical defect to which their extreme feebleness and early death can be attributed. {79}

FURROWED.

In studying the effect of hybridization upon the production of mutations in _Drosophila_, F. N. Duncan found a sex-linked mutation which he called "furrowed eye" (Duncan 1915). The furrowed flies are characterized by a foreshortening of the head, which causes the surface of the eye to be thrown into irregular folds with furrows between. The spines of the scutellum are stumpy, a character which is of importance in classification, since quite often flies occur which have no noticeable disturbance of the eyes.

The locus of furrowed was determined to be at 38.0 on the basis of the data given in table 61.

TABLE 61.--_Data on the linkage of furrowed, from Duncan, 1915_.

+------------+-------------------------------------------+------+
| Gens. | F_2 males. | |
+------------+---------+---------+-----------+-----------+ +
| | w^e m | w^e f_w | w^e m f_w | w^e |Total.|
| | ------- | --+---- | -----+--- | --+--+-- | |
| | f_w | m | | m f_w | |
| +---------+---------+-----------+-----------+------+
|Eosin, | | | | | |
| miniature,| | | | | |
| furrowed | 142 | 59 | 4 | 3 | 208 |
| +=========+=========+===========+===========+======+
| | f_w | f_w s f | f_w f | f_w s | |
| | ------- | --+---- | ----+- | --+--+-- | |
| | s f | | s | f | |
| |---------+---------+-----------+-----------+------+
|Furrowed, | | | | | ~
| sable, | | | | | ~
| forked | 166 | 9 | 31 | 3 | 209 |
| +=========+=========+===========+===========+======+
| | v B' | v f_w | v | v f_w B' | |
| | ------- | -+----- | ----+-- | -+---+-- | |
| | f_w | B' | f_w B' | | |
| +---------+---------+-----------+-----------+------+
|Vermilion, | | | | | |
| furrowed, | | | | | |
| bar | 188 | 9 | 43 | 0 | 240 |
+------------+---------+---------+-----------+-----------+------+

+------------------------------+
| Cross-over values. |
+----------+---------+---------+
|Eosin |Miniature|Eosin |
|miniature.|furrowed.|furrowed.|
| | | |
+----------+---------+---------+
| | | |
| | | |
| 29.8 | 30.4 | 30.3 |
+==========+=========+=========+
|Furrowed |Sable |Furrowed |
|sable. |forked. |forked. |
| | | |
+----------+---------+---------+
~ | | |
~ | | |
| 5.7 | 16.3 | 19.1 |
+==========+=========+=========+
|Vermilion |Furrowed |Vermilion|
|furrowed. |bar. |bar. |
| | | |
+----------+---------+---------+
| | | |
| | | |
| 3.8 | 21.6 | 17.9 |
+----------+---------+---------+

ADDITIONAL DATA FOR YELLOW, WHITE, VERMILION, AND MINIATURE.

Considerable new work has been done by various students upon the linkage of the older mutant characters, namely, yellow, white, vermilion, and miniature. We have summarized these new data, and they give values very close to those already published. We have included in the white miniature data those published by P. W. Whiting (Whiting 1913). {80}

TABLE 62.--_Data upon the linkage of yellow, white, vermilion, and miniature_ (_contributed by students_).

+--------------------+-----------------+-------------+-------+----------+
| Gens. | Non-cross-overs.| Cross-overs.| | |
+--------------------+-----------------+-------------+ | |
| | w m | w |Total. |Cross-over|
| | ------------- | -----+----- | |values. |
| | | m | | |
| +-----------------+-------------+-------+----------+
|White miniature. | 6,219[8] 7,378 | 3,754 3,337 |20,688 | 34.2 |
| +=================+=============+=======+==========+
| | w | w m | | |
| | ------------- | -----+----- | | |
| | m | | | |
| +-----------------+-------------+-------+----------+
| | 1,651 1,116 | 671 1,047 | 4,485 | 38.3 |
| +=================+=============+=======+==========+
| | y | y m | | |
| | ------------- | -----+----- | | |
| | m | | | |
| +-----------------+-------------+-------+----------+
|Yellow miniature. | 761 923 | 421 653 | 2,758 | 39 |
| +=================+=============+=======+==========+
| | v | v m | | |
| | ------------- | -----+----- | | |
| | m | | | |
| +-----------------+-------------+-------+----------+
|Vermilion miniature.| 1,685 1,460 | 32 36 | 3,213 | 2.1 |
| +=================+=============+=======+==========+
| | y w | y | | |
| | ------------- | -----+----- | | |
| | | w | | |
| +-----------------+-------------+-------+----------+
|Yellow white. | 1,600 1,807 | 10 7 | 3,424 | 0.5 |
| +=================+=============+=======+==========+
| | y v | y | | |
| | ------------- | -----+----- | | |
| | | v | | |
| +-----------------+-------------+-------+----------+
|Yellow vermilion. | 509 587 | 328 284 | 1,708 | 35.8 |
| +=================+=============+=======+==========+
| | w B' | w | | |
| | ------------- | -----+----- | | |
| | | B' | | |
| +-----------------+-------------+-------+----------+
|White bar. | 198 272 | 168 166 | 804 | 42 |
| +=================+=============+=======+==========+
| | b_1 | b_1 r | | |
| | ------------- | -----+----- | | |
| | r | | | |
| +-----------------+-------------+-------+----------+
|Bifid rudimentary. | 142 15 | 12 116 | 285 | 45 |
| +=================+=============+=======+==========+
| | r | r f | | |
| | ------------- | -----+----- | | |
| | f | | | |
| +-----------------+-------------+-------+----------+
|Rudimentary forked. | 73 211 | ... 4 | 288 | 1.4 |
+--------------------+-----------------+-------------+-------+----------+

{81}

NEW DATA CONTRIBUTED BY A. H. STURTEVANT AND H. J. MULLER.

Data from several experiments upon sex-linked characters described in this paper have been contributed by Dr. A. H. Sturtevant and Mr. H. J. Muller, and are given in table 63.

TABLE 63.--_Data contributed by A. H. Sturtevant and H. J. Muller._