200 



T. H. MORGAN. 



in the male contain both recessive factors and in consequence, 

 even with no crossing over in the male, the realization of a double 

 recessive zygote becomes possible. 



The expected ratio without linkage in the female is 5 : 1 : 1 : 1. 

 Four classes are expected and four appear, but the ratio given 

 above is entirely changed by the linkage of the factors which here, 

 on our assumption, lie in the same chromosome. 



PURPLE EYES AND VESTIGIAL WINGS. 



An eye color called purple also shows linkage with vestigial 

 and is placed, therefore, in the second group of factors. It has 

 likewise been used to test non-crossing over in the male. Purple 

 vestigial flies mated to red-eyed, long-winged flies gave red- 

 eyed, long-winged FI males and females. When these FI males 

 were bred to purple vestigial females only two classes were 

 produced : 



The result is explicable if no crossing over occurs in the male 

 and the analysis is the same in principle as that for the black 

 vestigial case. As explained before, every sperm contains one 

 or the other recessive since they went in separately and have not 

 crossed over in the male. 



\Vhen the FI females (sisters to the males just tested) were 

 mated to purple vestigial males, the following results were 

 obtained : 



Red Long. 

 2,876 



Purple Long. 

 270 



Red Vestigial. 

 270 



Purple Vestigial. 

 2,433 



The result is explicable on the hypothesis of crossing over 

 (about ten per cent.) in the female, as the analysis for the com- 

 parable case for black vestigial shows. 



