SEX-LINKED INHERITANCE IN DROSOPHILA 95 



LRBYX - LRByX - SVVYbX - SWybX ^ 



Sperm 



There were seven cases of crossing-over in 1466 males, and 

 three cases in 2282 females. In the males the three crossings in 

 one direction (LWN) are balanced by four crossings in the other 

 direction (LRY, and LRBr). The three cases in the females 

 (LRY) can not be explained by crossing-over in the eggs, since 

 all female-producing sperms carry the factor for black, hence no 

 yellow females are possible, unless one of these sperms should lose 

 the B factor, which would be a mutation. Hence the case is 

 due either to this, or to some error. 



In the wing characters we find LRN d' = 562, while SRN d" 

 = 266; LRB d^ = 163, while SRB cf = 53. On the other hand, 

 SWY cf = 371, while LWY cf =279; SWBr d^ = 184, while 

 LWBr cf = 78. The sum of the 'straight' males is 1280, and the 

 cross-overs 676, a ratio of about 2:1. 



