372 



LINKAGE PHENOMENA 



double recessive (i.e., a black vestigial), male, all four 

 phenotypes occur in the second hybrid generation, but 

 they do not occur in the 1:1:1:1 ratio to be expected in 

 the case of free assortment. If a female hybrid of type 

 (2) (i.e., offspring of gray vestigial by black long) is 

 mated to the double recessive (i.e., black vestigial) male, 



Parent I 



Gray 



vestigial 



Gl Gl 



m\ (Only one of 

 four chromo- 

 some pairs 

 shown) 



Parent II 



black 



Long 



gL gL 



A gray vestigial 

 sperm of 

 Parent I 



Si 



A black long 

 sperm of 

 Parent II 



The gray long hybrid 

 (male) 

 Gl gL 



Sperms of the 

 hybrid 



Gray vestigial 

 Gl 



black long 

 gL 



B 



Fro. 107. — (6) Showing the segregation of linked genes in gray 

 long hybrid of type Gl gL. 



the same four phenotypes occur but the ratios are again 

 different. In the first case there are about five times as 

 many Gray Long and black vestigial flies (i.e., grand- 

 parental combinations) as there are Gray vestigial and 

 black Long or recombination classes. In the second case 

 there are also about five times as many grandparental 

 types (i.e., this time Gray vestigial and black Long) as 



