Sex-linked Inheritance In Drosophila Part 4

w^e V s --+--------------------------------------------------+--------------+ X X --+--------------------------------------------------+--------------+ W v S

DIAGRAM II.--The upper line represents an X chromosome, the lower line its mate. The cross connecting lines indicate crossing-over between pairs of factors.

w^e s {Eosin sable.

Non-cross-overs -------------------------- { v {Vermilion.

w^e v {Eosin vermilion.

Single cross-overs ------------+------------- { s {Sable.

w {Eosin.

-----------------------+-- { v s {Vermilion sable.

w^e v s {Eosin vermilion sable.

Double cross-overs ------------+----------+-- { {Wild-type.

If we consider the female cla.s.ses of table 11, we get information as to the cross-over value of eosin and sable, namely, 42 units. The male cla.s.ses will be considered in connection with the cross that follows.

The next experiment involves the same three gens which now enter in different relations. A double recessive, eosin vermilion (gray) female {39} was mated to (red red) sable males and gave 202 wild-type[5] females and 184 eosin vermilion males. Two F_1 pairs gave the results shown in table 12 (the four cla.s.ses of females not being separated).

TABLE 12.--_P_1 eosin vermilion F_1 wild-type [female] F_1 eosin vermilion [male] [male]._

+------+--------+-------------------------------------------------------+ F_2 males. +-------------+-------------+-------------+-------------+ w^e v w^e s w^e v s w^e ----------- -----+----- --------+-- ----+---+-- Refer- F_2 s v v s ence. females.+------+------+------+------+------+------+------+------+ Eosin Eosin verm- Wild- Verm- verm- Sable. Eosin Verm- ilion type. Eosin. ilion ilion. [male] sable. ilion. sable. [male] [male] sable. [male] [male] [male] [male] [male] +------+--------+------+------+------+------+------+------+------+------+ 59 C 133 40 33 7 16 5 5 2 1 61 C 101 34 26 8 11 3 7 1 0 +--------+------+------+------+------+------+------+------+------+ Total 234 74 59 15 27 8 12 3 1 +------+--------+------+------+------+------+------+------+------+------+

If we combine the data for males given in table 12 with those of table 11, we get the following cross-over values. Eosin vermilion, 32; vermilion sable, 12; eosin sable, 41.

{40}

LINKAGE OF MINIATURE AND SABLE.

The miniature wing has been described (Morgan, Science, 1911) and the wing figured (Morgan, Jour. Exp. Zool., 1911). The gen for miniature lies about 3 units to the right of vermilion, so that it is still closer to sable than is vermilion. The double recessive, miniature sable, was made up, and males of this stock were bred to wild females (long gray). The wild-type daughters were back-crossed to double recessive males and gave the results (ma.s.s cultures) shown in table 13.

TABLE 13.--_P_1 wild [female] [female] miniature sable [male] [male]. B.

C. F_1 wild-type [female] [female] miniature sable [male] [male]._

+-----------+---------------------+-----------------+-------+-------+ Non-cross-overs. Cross-overs. Cross- Reference.+----------+----------+----------+------+ Total. over value. Miniature Wild-type. Miniature. Sable. sable. +-----------+----------+----------+----------+------+-------+-------+ 38 I 245 283 15 17 560 6 43 I 191 236 13 18 458 7 46 I 232 274 24 21 551 8 +----------+----------+----------+------+-------+-------+ Total 668 793 52 56 1,569 7 +-----------+----------+----------+----------+------+-------+-------+

Since the results for the male and the female cla.s.ses are expected to be the same, the s.e.xes were not separated. The combined data give 7 per cent of crossing-over between miniature and sable.

LINKAGE OF VERMILION, SABLE, AND BAR.

Bar eye has been described by Mrs. S. C. Tice (1914). It is a dominant s.e.x-linked character, whose locus, lying beyond vermilion and sable, is near the right end of the chromosome series, that is, at the end opposite yellow.

In the first cross of a balanced series of experiments for the gens vermilion, sable, and bar, vermilion (gray not-bar) entered from one side ([female]) and (red) sable bar from the other ([male]). The daughters were bar and the sons vermilion. The daughters were back-crossed singly to the triple recessive males vermilion sable (not-bar), and gave the data included in table 14.

In the second cross, vermilion sable (not-bar) went in from one side ([female]) and (red, gray) bar from the other. The daughters were bar and the sons were vermilion sable. Since these sons have the three recessive factors, inbreeding of F_1 is equivalent to a triple back-cross. The results are given by pairs in table 15. {41}

TABLE 14.--_P_1 vermilion [female] [female] sable bar [male] [male]. B.

C. F_1 bar [female] vermilion sable [male] [male]._

+------+------------+-----------+------------+-----------+ v v s B' v B' v s ---------- ---+----- -----+---- --+--+--- s B' s B' +------+-----+-----+-----+-----+------+------+----+ Refer- Verm- ence. Verm- Sable ilion Wild- Verm- Ver- ilion. bar. sable type. ilion Sable. milion Bar. bar. bar. sable. +------+------+-----+-----+-----+-----+------+------+----+ 147 I 81 66 12 15 15 18 ~ 148 I 103 108 4 19 11 11 ~ 149 I 97 88 10 8 17 17 1 1 150 I 95 75 10 11 21 22 1 1 151 I 116 96 11 15 23 26 2 89 89 94 10 19 15 11 1 90 49 50 4 8 15 14 91 104 88 13 15 12 12 +------+-----+-----+-----+-----+------+------+----+ Total. 734 665 74 110 129 131 3 4 +------+------+-----+-----+-----+-----+------+------+----+

+------+------+------------------+ Cross-over values. +------+-----+-----+ Refer- Total. ence. Verm- Verm- ilion Sable ilion sable. bar. bar. +------+------+------+-----+-----+ ~147 I 207 13 16 29 ~148 I 256 9 9 18 149 I 239 8 15 22 150 I 236 10 19 27 151 I 289 10 18 26 89 239 13 11 23 90 140 9 21 29 91 244 11 10 21 +------+------+-----+-----+ Total. 1,850 10 14 24 +------+------+------+-----+-----+

TABLE 15.--_P_1 vermilion sable [female] [female] bar [male] [male]. B.

C. F_1 bar [female] vermilion sable [male] [male]._

+------+----------+------------+-----------+------------+ v s v B' v s B' v -------- ---+------ -----+--- --+---+--- B' s s B' +------+---+-----+------+-----+-----+------+-----+ Refer- Verm- ence. Verm- Verm- ilion Wild- Verm- Sable ilion Bar ilion Sable. sable type. ilion. bar. sable. bar. bar. +------+------+---+-----+------+-----+-----+------+-----+ 105 I 41 75 10 4 5 11 ~ 106 I 59 122 16 13 11 17 ~ 107 I 92 98 8 12 16 10 116 I 111 149 19 16 20 19 1 117 I 92 117 16 14 15 18 126 I 96 160 13 13 17 35 127 I 117 124 13 25 24 30 1 +------+---+-----+------+-----+-----+------+-----+ Total 608 845 95 97 108 140 1 1 +------+------+---+-----+------+-----+-----+------+-----+

+------+------+------------------+ Cross-over values. +------+-----+-----+ Refer- Total. ence. Verm- Verm- ilion. Sable ilion sable. bar. bar. +------+------+------+-----+-----+ ~105 I 146 10 11 21 ~106 I 238 12 12 24 107 I 236 9 11 20 116 I 335 11 12 22 117 I 272 11 12 23 126 I 334 8 15 23 127 I 334 12 16 28 +------+------+-----+-----+ Total 1,895 10 13 23 +------+------+------+-----+-----+

{42}

In the third cross, vermilion (gray) bar entered from one side ([female]) and (red) sable (not-bar) from the other ([male]). The daughters are bar and the sons vermilion bar. The daughters were back-crossed singly to vermilion sable males and gave the data in table 16.

TABLE 16.--_P_1 vermilion bar_ [female] [female] _sable_ [male] [male].

_B. C. F_1 bar_ [female] _vermilion sable_ [male] [male].

+-----------+--------------+------------+-------------+---------------+ v B' v s v v s B' ----- -+------ -----+-- -+---+-- Reference. s B' s B' +-------+------+------+-----+-------+-----+---------+-----+ Ver- Sable. Ver- Bar. Ver- Sable Vermilion Wild- milion milion milion. bar. sable type. bar. sable. bar. +-----------+-------+------+------+-----+-------+-----+---------+-----+ 129 I 132 147 15 15 19 21 1 1 ~ 130 I 194 168 21 17 28 25 .. 1 ~ 131 I 121 89 10 20 26 11 1 1 137 I 139 113 19 12 33 14 .. 1 138 I 131 128 11 11 28 24 1 .. 139 I 83 79 4 12 17 12 .. .. +-------+------+------+-----+-------+-----+---------+-----+ Total. 800 724 80 87 151 107 3 4 +-----------+-------+------+------+-----+-------+-----+---------+-----+

+-----------+-------+-------------------------+ Reference. Total. Cross-over values. +---------+-----+---------+ Vermilion Sable Vermilion sable. bar. bar. +-----------+-------+---------+-----+---------+ ~ 129 I 351 9 12 20 ~ 130 I 454 9 12 20 131 I 279 12 14 24 137 I 331 10 15 24 138 I 334 7 16 22 139 I 207 8 14 22 +-------+---------+-----+---------+ Total. 1,956 9 14 22 +-----------+-------+---------+-----+---------+

In the fourth cross, vermilion sable bar entered from one side, and (red gray not-bar) wild type from the other. The daughters were bar and the sons vermilion sable bar. The daughters were back-crossed singly to vermilion sable males, with the results shown in table 17.

TABLE 17.--_P_1 vermilion sable bar_ [female] [female] _wild_ [male]

[male]. _B. C. F_1 bar_ [female] _vermilion sable_ [male] [male].

+-----------+---------------+--------------+------------+--------------+ v s B' v v s v B' -------- -+----- -----+-- -+-+-- Reference. s B' B' s +---------+-----+--------+-----+-------+----+-------+------+ Vermilion Wild- Ver- Sable Ver- Bar. Ver- Sable. sable type milion. bar. milion milion bar. sable. bar. +-----------+---------+-----+--------+-----+-------+----+-------+------+ 132 I 95 108 10 13 24 22 .. .. ~ 133 I 112 150 18 16 26 16 1 2 ~ 134 I 84 95 14 7 15 16 .. 1 135 I 100 86 16 17 19 22 .. 1 152 I 73 88 12 8 14 18 .. .. 153 I 114 138 12 12 17 17 .. .. 154 I 63 90 10 8 8 15 .. .. Total. 641 755 92 81 123 126 1 4 +-----------+---------+-----+--------+-----+-------+----+-------+------+

+-----------+------+-------------------------+ Reference. Total. Cross-over values. +---------+-----+---------+ Vermilion Sable Vermilion sable. bar. bar. +-----------+------+---------+-----+---------+ ~ 132 I 272 9 17 25 ~ 133 I 341 11 13 22 134 I 232 10 14 22 135 I 261 13 16 28 152 I 213 9 15 24 153 I 310 8 11 19 154 I 194 9 12 21 Total. 1,823 10 14 23 +-----------+------+---------+-----+---------+

{43}

In tables 14 to 17 the calculations for the three cross-over values for vermilion, sable, and bar are given for the separate cultures and for the totals. The latter are here repeated.

+-----------+-----------+---------+-----------+ From-- Vermilion Sable Vermilion sable. bar. bar. +-----------+-----------+---------+-----------+ Table 14 10 14 24 15 10 13 23 16 9 14 22 17 10 14 23 +-----------+-----------+---------+-----------+

The results of the different experiments are remarkably uniform. There can be no doubt that the cross-over value is independent of the way in which the experiment is made, whether any two recessives enter from the same or from opposite sides.

TABLE 18.--_Linkage of vermilion, sable, and bar with balanced viability._

+---------------------+---------+---------+---------+---------+-------+ ------- --+---- ----+-- --+-+-- Total. +---------------------+---------+---------+---------+---------+-------+ Wild-type 755 110 140 4 Vermilion 734 92 151 1 Sable 724 97 131 4 Bar 845 87 126 4 Vermilion sable 608 80 123 3 Vermilion bar 800 95 129 1 Sable bar 665 81 107 1 Vermilion sable bar 641 74 108 3 +---------+---------+---------+---------+-------+ Total 5,772 716 1,015 21 7,524 Percentage 76.7 9.53 13.49 0.28 +---------------------+---------+---------+---------+---------+-------+

In table 18 the data from each of the four separate experiments have been combined in the manner explained, so that viability is canceled to the greatest extent. The amount of each kind of cross-over appears at the bottom of the table. The total amount of crossing-over between vermilion and sable is the sum of the single (9.53) and of the double (0.28) cross-overs, which value is 9.8. Likewise the cross-over value for sable bar is 13.49 + 0.28 (= 14), and for vermilion bar is 9.53 + 13.49 (= 23).

By means of these cross-over values we may calculate the coincidence involved, which is in this case

0.0028 100 --------------------------------- = 20.8 0.0953 + 0.0028 0.1349 + 0.0028

This value shows that there actually occurs only about 21 per cent of the double cross-overs which from the values of the single cross-overs are expected to occur in this section of the chromosome. This is the result which is to be antic.i.p.ated upon the chromosome view, for if crossing-over is connected with loops of the chromosomes, and if these loops have an average length, then if the chromosomes cross over at one {44} point it is unlikely they will cross over again at another point nearer than the average length of the loop.