SEX-CH'EOMOSOMES xVND INHERITANCE 173 



character of his single Z-chromosome, and there are four 

 kinds of these chromosomes in his mother on account of 

 crossing over in the female. The other sex-chromosome, 

 the r, has no dominating influence. 



Fig. 72. — The fa results from the reeiprccal cross of that shown in Fig. 71. 



Sex-linked Inheritance oe the Abeaxas Type 

 In certain moths and birds it has been shown by the 

 genetic evidence that the female is heterozygous for sex- 

 linked factors. The cytological evidence, as far as it goes, 

 supports this evidence, but for birds the material is so 



