SEX-CHARACTERS IN EVOLUTION 117 



chromosome, and use the black rod for the dominant 

 character : — 



10 



BARRED (5 



Heterozygous. 



UNBARRED Cj 



00 







U A/ BARRED Q 



Homozygous. 



BARRED Q 



Heterozygous. 



Another case is that of tortoise-sliell, i,e, black 

 and yellow cats. The tortoise-shell with very rare 

 exceptions is female, the corresponding male being 

 yellow, without any black colour. Doncaster found 

 that a yellow male mated to a black female produced 

 black male offspring and tortoise-shell females. 



