No. 576] 



VARIATION IN DROSOPHILA 



755 



had, however, been done to show definitely the nature of 

 the mutation involved. It is clear that the perfect notched 

 wings owed their appearance to a dominant sex-linked 

 gene, lethal for males. This accounts for the fact that 

 the males are only half as numerous as the females, and 

 none of them notched, while notched and normal females 

 occur in nearly equal numbers. It also accounts for the 

 fact that the normal females of these generations gave no 

 notched offspring. 



Other sex-linked lethal genes have appeared from time 

 to time in the crosses of Beaded flies with others, but 

 none of them were dominant, and therefore they made 

 themselves evident only by preventing the development 

 of one half of fhe males. I have not worked out the 

 inheritance of these cases. 



C. Spread Wings 

 Comment has already been made on the extreme num- 

 ber of wing types that appeared both in the F 1? F 2 , and 

 back-cross generations of the cross between Beaded and 

 Vestigial flies. Most of these forms gave results too com- 

 plex to be analyzed at present. However, among the off- 

 spring of a considerable number of the F, females there 

 were flies with wings perfectly normal in appearance save 

 that they were held at right angles to the long axis of the 

 body. In all, 60 flies with Spread wings appeared. One 

 of the 60 had wings very slightly Beaded. Some of them 

 were mated together and produced only spread-winged 

 offspring with no sign of Beadedness. Spread-winged 

 males were mated to Pink Black females in order to test 

 the linkage of Spread. (Pink is in the third chromosome 

 group, and Black in the second. ) The F, generation gave 

 onlv flies with red eyes, gray bodies and normal wings 

 (neither Spread nor Beaded). In the F 2 generation were 

 Black flies, Gray flies, and Bed-eyed flies with normal 

 and with Spread wings, but none of the Pink-eyed flies 

 had Spread wings, though a large number of F, Pink 

 normal flies appeared. The Pink-eyed flies were also 

 mated inter se, but no Spread-winged flies appeared in 

 the F 3 generation. This definitely places the gene for 



