In the crosses between white and bifid there were 1,127 cross-overs in a total of 20,800 available individuals, which gives a cross-over value of 5.3. In the crosses between yellow and bifid there were 182 cross-overs in a total of 3,175 available individuals, which gives a cross-over value of 5.8. In crosses between bifid and vermilion there were 806 cross-overs in a total of 2,509, which gives a cross-over value of 32.1. On the basis of all the data summarized in table 65, bifid is located at 6.3 to the right of yellow.
LINKAGE OF CHERRY, BIFID, AND VERMILION.
In a small experiment of our own, three factors were involved—cherry, bifid, and vermilion. A cherry vermilion female was crossed to a bifid male. Two daughters were back-crossed singly to white bifid males. The female offspring will then give data for the linkage of cherry white with bifid, while the sons will show the linkage of the three gens, cherry, bifid, and vermilion. The results are shown in table 3.
Table 3.—P1 cherry vermilion ♀ ♀ × bifid ♂ ♂. B. C.[[2]] F1 wild-type ♀ × white bifid ♂ ♂.
| Refer- ence. | F2 females. | F2 males. | ||||||||||
| Non-cross- overs. | Cross-overs. |
|
|
|
| |||||||
| White- cherry | Bifid. | White- cherry bifid. | Wild- type. | Cherry ver- milion. | Bifid. | Cherry bifid. | Ver- milion. | Cherry. | Bifid ver- milion. | Cherry bifid vermilion. | Wild- type. | |
| 262 | 40 | 46 | 1 | 2 | 45 | 38 | 3 | 2 | 11 | 13 | .. | .. |
| 263 | 47 | 45 | 3 | 3 | 30 | 50 | 1 | 3 | 8 | 10 | 1 | .. |
| Total. | 87 | 91 | 4 | 5 | 75 | 88 | 4 | 5 | 19 | 23 | 1 | 0 |
Both males and females give a cross-over value of 5 units for cherry bifid, which is the value determined by Chambers. The order of the factors, viz, cherry, bifid, vermilion, is established by taking advantage of the double cross-over classes in the males. The male classes give a cross-over value of 20 for bifid vermilion and 24 for cherry vermilion, which are low compared with values given by other experiments. The locus of bifid at 6.3 is convenient for many linkage problems, but this advantage is largely offset by the liability of the bifid flies to become stuck in the food and against the sides of the bottle. Bifid flies can be separated from the normal with certainty and with great ease.
REDUPLICATED LEGS.
In November 1912 Miss Mildred Hoge found that a certain stock was giving some males whose legs were reduplicated, either completely or only with respect to the terminal segments (described and figured, Hoge, 1915). Subsequent work by Miss Hoge showed that the condition was due to a sex-linked gen, but that at room temperature not all the flies that were genetically reduplicated showed reduplication. However, if the flies were raised through the pupa stage in the ice-box at a temperature of about 10° to 12° a majority of the flies which were expected to show reduplication did so. The most extremely reduplicated individual showed parts of 14 legs.
In studying the cross-over values of reduplicated, only those flies that have abnormal legs are to be used in calculation, as in the case of abnormal abdomen where the phenotypically normal individuals are partly genetically abnormal. Table 4 gives a summary of the data secured by Miss Hoge.