HEREDITY AND VARIATION 



are produced by crossing a type of black fowl with a certain kind of white 

 fowl. They are, therefore, hybrids and, as would be anticipated, do not breed 

 true. Blue Andalusian parents yield 25 per cent black chicks, 50 per cent 

 blue chicks, and 25 per cent white chicks. The black and the white offspring 

 breed true, but the blue ofTspring, like all other Blue Andalusians, will always 

 yield 25 per cent black, 50 per cent blue, and 25 per cent white individuals. 

 The course of inheritance for characteristics that do not exhibit dominance is 

 in no way different, therefore, from that for characteristics in which domi- 

 nance occurs. In inheritance without dominance, the hybrid individuals, or 

 those that will not breed true, can be distinguished .superficially from those 

 that will give rise to offspring like themselves. Dominance is not an essential 



Black fowl 



Splashed- white fowl 



A'^T^v: 



Blue 



Andalusian 



fowls 



Intercrossed 



1 black fowl 



2 blue Andalusian fowls 



1 splashed -white fowl 



Fig. 6.5. Results of monohybridization of fowls which differ in color of feathers. This is 

 an example of inheritance without dominance, since black and white parents yield blue hybrids. 

 In the F2 generation three visibly distinct types are produced in a 1 : 2 : 1 ratio. 



179 



