The data from the males show that the locus of club is about midway between yellow and vermilion. This conclusion is based on the
evidence that yellow and club give 18 per cent of crossing-over, club and vermilion 20 per cent, and yellow and vermilion 35 per cent. The double cross-overs on this view are yellow club (3) and vermilion (3). The females furnish additional data for the linkage of club and vermilion. The value calculated from the female classes alone is 20 units, which is the same value as that given by the males.
Table 51.—P1 club ♀ ♀ × vermilion ♂ ♂. F1 wild-type ♀ × F1 club ♂.
| Reference. | Females. | Non-cross-over ♂ ♂. | Cross-over ♂ ♂. | Total ♂ ♂. | Cross- over values. | ||
| Club. | Ver- milion. | Club Vermilion. | Wild- type. | ||||
| 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.—P1 club vermilion ♀ ♀ × yellow ♂ ♂. F1 wild-type ♀ ♀ × F1 club vermilion ♂ ♂.
| Reference. | F2 females. | F2 males. | ||||||||||
| Non-cross- overs. | Cross-overs. |
|
|
|
| |||||||
| Club ver- milion. | Wild- type. | Club. | Ver- milion. | Yellow. | Club ver- milion. | Yellow club ver- milion. | Wild- type. | Yellow ver- milion. | Club. | Yellow Club. | Ver- milion. | |
| 99 | 44 | 52 | 13 | 7 | 35 | 27 | 2 | 9 | 8 | 11 | 0 | 1 |
| 100 | 38 | 58 | 6 | 12 | 43 | 23 | 1 | 15 | 11 | 14 | 0 | 0 |
| 101 | 30 | 32 | 6 | 12 | 19 | 24 | 6 | 5 | 10 | 3 | 1 | 0 |
| 102 | 44 | 55 | 20 | 13 | 48 | 38 | 12 | 14 | 8 | 15 | 1 | 1 |
| 103 | ... | ... | ... | ... | 43 | 32 | 7 | 16 | 13 | 7 | 1 | 1 |
| Total. | 156 | 197 | 45 | 44 | 188 | 144 | 28 | 59 | 50 | 50 | 3 | 3 |
LINKAGE OF CHERRY, CLUB, AND VERMILION.
The need for a readily workable character whose gen should lie in the long space 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.