Since forked arose in vermilion stock, the double recessive for these two sex-linked factors could be used in testing the linkage relations of the mutation. Vermilion forked males were crossed to wild females and gave wild-type males and females, which inbred gave in F2 the results shown in table 39. Forked reappeared only in the males in the following proportion: not-forked ♀, 742; not-forked ♂, 346; forked ♂, 301. The result shows that the character is a sex-linked recessive.

Table 39.—P1 wild ♀ ♀ × vermilion-forked ♂ ♂. F1 wild-type ♀ ♀ × F1 wild-type ♂ ♂.

Reference. Wild-type
♀♀.		 Non-cross-over ♂ ♂. Cross-over ♂ ♂. Total
♂ ♂.		 Cross-
over
values.
Vermilion
forked.		 Wild-
type.		 Vermilion. Forked.
9 I 366 113 123 49 41 326 28
11 I 376 116 150 42 31 339 22
Total. 742 229 273 91 72 665 25

In table 39 vermilion forked and wild-type are non-cross-overs, and vermilion and forked are cross-overs, giving a cross-over value of 25 units. The locus, therefore, is 25 units to the right or to the left of vermilion, that is, either about 58 or 8 units from the yellow locus.

LINKAGE OF CHERRY AND FORKED.

Forked males were crossed to cherry females (cherry has the same locus as white, which is about 1 unit from yellow) and gave wild-type females and cherry males. These gave in F2 the results shown in table 40. The non-cross-overs (cherry and forked) plus the cross-overs (cherry forked and wild type) divided into the cross-overs give a cross-over value of 46 units, which shows that the locus lies to the right of vermilion, because if it had been to the left, the value would have been 8 (i. e., 33-25) instead of 33+25=58. The difference between 58

and 46 is due to the expected amount of double crossing-over. In fact, for a distance as long as 58 an almost independent behavior of linked gens is to be expected.

Table 40.—P1 cherry ♀ ♀ × forked ♂ ♂. F1 wild-type ♀ ♀ × F1 cherry ♂ ♂.

Reference. Females. Non-cross-over ♂ ♂. Cross-over ♂ ♂. Total
♂ ♂.		 Cross-
over
values.
Cherry. Wild-
type.		 Cherry. Forked. Cherry
forked.		 Wild-
type.
25 129 145 73 70 65 68 276 48
25′ 167 148 74 82 66 88 310 50
36 96 88 52 52 35 51 190 45
36′ 57 76 41 32 24 30 127 43
84 76 86 40 34 38 26 138 46
84′ 62 71 24 39 25 28 116 46
85 114 86 43 78 41 53 215 44
85′ 98 95 48 63 52 46 209 47
86 307 323 152 144 118 165 579 49
87 351 341 183 213 160 147 703 45
88 244 246 142 142 107 104 495 43
Total. 1,701 1,705 872 949 731 806 3,358 46