yo SEX-LINKED INHERITANCE IN DROSOPHILA. 



5,352; wild-type cf, 4,181; club 6^,236. The wild-type males include, 

 of course, those club males that have expanded wings (potential clubs).' 



Club females by wild males gave in the F2 generation (mass cultures) : 

 wild-type 9, 1,131; wild-type cf", 897; club 9, 57; club cf, 131. 



It is noticeable that there were fewer club females than club males, 

 equality being expected, which might appear to indicate that the club 

 condition is more often realized by the male than by the female, but 

 later crosses show that the difference here is not a constant feature of 

 the cross. 



Long-winged males from club stock (potential clubs) bred to wild 

 females gave in F2 the following: wild-type 9, 521; wild-type (and 

 potential club) 0^,403; club 0^,82. 



Club females by club males of club stock gave in Fa : potential club 9 , 

 126; potential club c?, 78; clUb 9, 95; club cT, 81. These results are 

 from 8 pairs. The high proportion of club is noticeable. 



Potential club females and males from pure club stock {i. e., stock 

 derived originally from a pair of club) gave in Fg the following: potential 

 club 9, 1,049; potential club cT, 666; club 9,450; club cf, 453. 



GENOTYPIC CLUB. 



Accurate work with the club character was made possible by the 

 discovery of a character that is a constant index of the presence of 

 homozygous club. This character is the absence of the two large 

 bristles (text-fig. hc) that are present on each side of the thorax of 

 the wild fly as shown in figure nb. All club flies are now classified by 

 this character and no attention is paid to whether the wings remain 

 as pads or become expanded. 



LINKAGE OF CLUB AND VERMILION. 



The linkage of club and vermilion is shown by the cultures listed in 

 table 51, which were obtained as controls in working with lethal III. 

 The cross-over value is shown in the male classes by the cross-over 



fraction — ^ or 19 per cent. 



LINKAGE OF YELLOW, CLUB, AND VERMILION. 



The data just given in table 50 show that club is 19 units from 

 vermilion, but in order to determine in which direction from vermilion 

 it lies, the crossing-over of club to one other gen must be tested. 

 For this test we used yellow, which lies at the extreme left of the chro- 

 mosome series. At the same time we included vermilion, so that a 

 three-point experiment was made. 



Females that were (gray) club vermilion were bred to yellow (not- 

 club red) and gave wild-type daughters and club vermilion sons. 

 These inbred gave the results of table 52. 



The data from the males show that the locus of club is about midway 

 between yellow and vermilion. This conclusion is based on the evi- 



