70 HEREDITY [ch. v 



tions of selection breeders have tried without success 

 to eliminate these black and white 'wasters/ but it 

 remained for Bateson and Punnett to show that if 

 a black and a white are paired together, only blues 

 are produced. The two homozygotes are black and 

 white respectively ; when these are paired together 

 the single black factor introduced from one parent 

 is insufficient to cause the crossed chicks to be full 

 black, and a dilute black or 'blue' results. Such 

 incomplete dominance, in which a single factor 

 introduced from one parent is insufficient to bring 

 about the same effect in the heterozygote that is 

 produced by the 'double dose' present in the 

 homozygote, has been observed in a number of cases, 

 some of which must be referred to later. 



