190 



EVOLUTION AND GENETICS 



namely, that the differences are due to other modi- 

 fying genes that affect the extent to which the 

 character develops. 



mo 



1 i 1 i L, 



oAii 



« 



DtO ChO 



i^i 



aioinii 



t^ 



Fig. 71. — Two pedigrees for color- 

 blindness. {After Lenz.) 



Blue eyes in man behaves as a recessive to brown 

 eyes. Two blue-eyed parents have only blue-eyed 

 children {fig. 72). Pure brown-eyed individuals 



