Uereditv and Sex 



75 



f^m alp I't^ tVip hpternzyg-Qiis sex . The same is_true 

 limited inh eritance in canary birds and in the ninth, Ahnixa sj 

 according to Bateson and Doncaster. But these relations are I < 

 exacClj^reversed m the pomace fly, Drosophila anipelophila V 

 according to Morgan. 



In Drosophjla the^fgni ale is app arently ho mozygous as 

 regards some cell structure, .Y, which in t he male jsjie\^er 

 representedjnore than 



\ 



Female 



Male 



once. Accordingly, 

 the formula of the 

 female is in such cases 

 XA'; that of the male, 

 A' — . NoAv the sex- 

 limited characters in 

 Drosophila seem to be 

 bound up with the X 

 structure, not repelled 

 by it, as is barring in 

 fowls. Accordingly, a 

 sex -limited character 

 may be represented 

 twice in the female 

 Drosophila, but only 

 once in the male; or in other words, the female may be 

 homozygous as regards a sex-limited character, but the 

 male can only be heterozygous (P^ig. 38). 



Drosophila normally has red eyes, but the redness of 

 the eye is a distinct unit-character, sex limited in heredity. 

 Further, males are regularly heterozygous in this character, 

 while females are homozygous. For Morgan has obtained 

 a race in which the eyes are white, owing to the loss of the 

 red character; and reciprocal crosses of this race with 



Fig. 3S. — Diagram of sex-limited inheritance 

 when the female is a homozygote, as in the red- 

 eyed Drosophila. X, sex determiner; R, red 



eyes. 



