BLENDING INHERITANCE 169 



single dose of the determiner in such a case has plainly, 

 then, less phenotypic effect than a double dose. 



There are many instances of imperfect dominance 

 among flowering plants. Correns* red and white four- 

 o'clocks with pink offspring (p. 106) is a case in hand. 



A classic illustration of imperfect dominance among 

 animals is the "blue Andalusian fowl," the hereditary 

 behavior of which is illustrated below (Fig. 35). It 

 will be seen that when two blue Andalusian fowls, 



Andalusian Andalusian 



j i r i 



Black Andalusian Andalusian Splashed White 



\ 



I: . I II 



Black Andalusian Andalusian Spl. White Spl.White 



Andalusian 



FIG. 35. The heredity of the blue Andalusian fowl, an illustra- 

 tion of "imperfect dominance." 

 I 



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 fur- 

 ther breeding, to be homozygous, while the blue Anda- 

 lusian itself is heterozygous and can, therefore, 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 Andalusian. 

 There is nothing in this case to indicate whether the 



