SEX-CHARACTERS IN EVOLUTION 117 



chromosome, and use the black rod for the dominant 

 character : 



Heterozygous. 



UNBAftRED C? 



00 



Heterozygous, 



Another case is that of tortoise-shell, 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. 



