SEX-LINKED INHERITANCE IN DROSOPHILA 87 



both sexes count in the ratio. This gives 9 to 1477 or 1 to 164. 

 These cases are all in one direction. The missing counter-crosses 

 should be Red-yellows. 



The remaining cross involves the same combinations as one of 

 the preceding, but the R and B factors are present in the gray 

 fly. Therefore no crossing-over would be visible. Six large 

 classes are expected: 



LWB o^ by LRN 9 



Fi LRN (intermediate) 9 and cf = 1085 



LRN 9 = 2714 



LRN cf = 1541 



LWN cf = 1033 



' LRB 9 = 793 



LRB d" = 330 



LWB cf = 305 



The analysis follows: 



RBYX - RBYX Red gray 9 

 WByX - VVby White black cf 



Fi 



RBYXWByX Red gray 9 

 RBYXWby Red gray d' 



Gametes of Fi 



RByX - RBYX - WByX - WBYX 

 RByX - RBYX - Wby - WbY 



In the last case no evidence of crossing-over in the eye factors 

 is expected; for, the normal and black flies are alike in that they 

 carry the sex-linked factor for black. The yellow factor, it is 

 true, is absent from Black and present in Normal, but it shows 

 no linkage with White or with Red, which is in accord with the 

 hypothesis here followed. 



