Sex-linked Inheritance In Drosophila Part 8

LINKAGE OF FORKED, BAR, AND FUSED.

This value of 58 gave the furthest locus to the right obtained up to that time, since forked is slightly beyond rudimentary. Later, the locus for bar-eye was found still farther to the right, and the locus for fused even farther to the right than bar. A cross was made involving these three gens.

A forked (not-bar) fused male was bred to a (not-forked) bar (not-fused) female and gave bar females and males. The F_1 females were back-crossed singly to forked fused males with the result shown in table 41.

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

C. F_1 bar_ [female] _forked fused_ [male] [male].

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

{60}

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

TABLE 42.--_P_1 forked_ [female] [female] _bar fused_ [male] [male].

_B.C. F_1 bar_ [female] _forked fused_ [male] [male].

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

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

TABLE 43.

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

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

LINKAGE OF SABLE, RUDIMENTARY, AND FORKED.

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

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

_F_{1} wild-type_ [female] _F_{1} wild-type_ [male] [male].

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

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

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

LINKAGE OF RUDIMENTARY, FORKED, AND BAR.

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

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

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

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

SHIFTED.

Shifted appeared (January 1913) in a stock culture of vermilion dot. The chief characteristic of this mutant is that the third longitudinal vein (see text-fig. F) does not reach the margin as it does in the normal fly.

The vein is displaced toward the fourth throughout its length, and only very rarely does it extend far enough to join the marginal vein. The cross-vein between the third and the fourth veins is often absent because of the shifting. The flies themselves are smaller than normal. The wings are held out from the body at a wide angle. The two posterior bristles of the scutellum are much reduced in size and stick straight up--a useful landmark by which just-hatched shifted flies may be recognized, even though the wings are not expanded.

LINKAGE OF SHIFTED AND VERMILION.

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

[Ill.u.s.tration: FIG. F.--Shifted venation. The third longitudinal vein is shifted toward the fourth and fails to reach the margin. Cross-vein between third and fourth longitudinal veins is lacking.]

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

TABLE 46.--_P_1 shifted vermilion [male] [male] wild [female] [female].

F_1 wild-type [female] F_1 wild-type [male] [male]._

Key to columns:

A: Wild-type [female] [female].

B: Non-cross-over [male] [male], Shifted.

C: Non-cross-over [male] [male], Wild-type.

D: Cross-over [male] [male], Shifted.

E: Cross-over [male] [male], Wild-type.

F: Total [male] [male].

G: Cross-over values.

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

{63}

LINKAGE OF SHIFTED, VERMILION, AND BAR.

In order to determine on which side of vermilion shifted lies, a shifted vermilion (not-bar) female was crossed to a (not-shifted red) bar male.

Three factors are involved, of which one, bar, is dominant. The shifted vermilion (not-bar) stock is a triple recessive, and a three-point back-cross was therefore possible. The daughters were bar and the sons were shifted vermilion (the triple recessive). Inbred these gave the results shown in table 46. The smallest cla.s.ses (double cross-overs) are shifted and vermilion bar, which places shifted to the left of vermilion at approximately 17.8 units from yellow.

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

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

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

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

LETHALS SA AND SB.

The first lethal found by Miss Rawls was in a stock that had been bred for about 3 years. While there was no _a priori_ reason that could be given to support the view that lethal mutations would occur more frequently among flies inbred in confinement, nevertheless a hundred females from each of several newly caught and from each of several confined stocks were examined for lethals (Stark, 1915). No lethals were found among the wild stocks, but 4 were found among the confined stocks. Whether this difference is significant is perhaps open to question. The first lethal was found in January 1913, in a stock that had been caught at Falmouth, Ma.s.sachusetts, 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]