Sex-linked Inheritance In Drosophila Part 10

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

TABLE 52.--_P_1 club vermilion_ [female] [female] _yellow_ [male] [male].

_F_1 wild-type_ [female] [female] _F_1 club vermilion_ [male] [male].

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

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

{71}

LINKAGE OF CHERRY, CLUB, AND VERMILION.

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

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

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

Table 53 gives the results.

TABLE 53.--_P_{1} cherry_ [female] [female] _club vermilion_ [male]

[male]. _B. C. F__{1} _wild-type_ [female] _cherry club vermilion_ [male]

[male].

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

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

{72}

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

TABLE 54.--_P_{1} cherry club vermilion_ [male] [male]. [female] [female]

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

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

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

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

GREEN.

In May 1913 there appeared in a culture of flies with gray body-color a few males with a greenish-black tinge to the body and legs. The trident pattern on the thorax, which is almost invisible in many wild flies, was here quite marked. A green male was mated to wild females and gave in F_2 a close approach to a 2:1:1 ratio. The green reappeared only in the F_2 males, but the separation of green from gray was not as easy or complete as desirable.

From subsequent generations a pure stock of green was made. A green female by wild male gave 138 wild-type females and 127 males which were greenish.

This green color varies somewhat in depth, so that some of these F_1 males could not have been separated with certainty from a mixed culture of green and gray males.

The results of these two experiments show that green is a s.e.x-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 s.e.xual 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 s.e.x-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 ma.s.s 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 s.e.x-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 repet.i.tion 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 cla.s.ses (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 s.e.x-ratio, vermilion females were bred to club males. Several such females gave s.e.x-ratios. Their daughters were again mated to vermilion males. Half of these daughters gave high female s.e.x-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 s.e.x-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 cla.s.ses 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] s.e.x-ratios (Morgan, 1914_b_, p. 92). The yellow white cla.s.s, which was a non-cross-over cla.s.s 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 s.p.a.ce 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 s.e.x-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 dest.i.tute 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 s.e.x-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 s.e.x-linked, another, speck, is in the second chromosome, and maroon is in the third chromosome. All eight F_2 cla.s.ses are therefore expected to be equal in size, and each pair of characters should show free a.s.sortment, that is, 50 per cent. The a.s.sortment value for facet speck is 48, for speck maroon 52, and for facet maroon 48, as calculated from the F_2 males of table 58.

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

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

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

LINKAGE OF FACET, VERMILION AND SABLE.