176 



GENETICS 



characterized by a mottled plumage, are bred together, 

 they produce three kinds of offspring in the ratio of 

 1:2:1. Twenty-five per cent are clear black, 50 per 

 cent are blue Andalusian, and 25 per cent are white 

 "splashed" with black. Both the black and the 

 splashed white fowls from this cross prove, upon 

 further breeding, to be homozygous, while the blue 

 Andalusian itself is heterozygous and can, therefore, 



Andalusian 



Andalusian 



r ~r 



Black Andalusian 



flndalusian Sptoshed White 



r r \ 



flndalusian Spi. While SpLWHiU 



Andalusian 



FIG. 51. The heredity of the blue Andalusian fowl, an illustration of 

 "imperfect dominance." 



never be made to breed true. In order to produce 

 100 per cent of blue Andalusian chicks, it is necessary 

 simply to cross a splashed white with a black Anda- 

 lusian. 



There is nothing in this case to indicate whether the 

 black or the splashed white should be regarded as 

 the homozygous dominant, since dominance is im- 

 perfect. In either case the heterozygous blue Anda- 

 lusian is at once evident in the first filial generation 

 without further crossing. 



A similar case of imperfect dominance is furnished 

 by the roan color of cattle which results when red 

 and white are crossed. If two roans are mated, they 



