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]
