468 



GENETICS 



the pink always give three kinds of offspring in the typical 1:2:1 

 ratio. Another case of inheritance without dominance is that of 

 the blue Andalusian fowl (Fig. 246). Blue Andalusian fowls are 

 produced by crossing a type of black fowl with a type of white fowl. 

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

 breed true. Blue Andalusian parents yield 25 per cent black 



BLACK -HAIRED, SMOOTH - 

 COATED GUINEA PIG 



WHITE-HAIRED, ROUGH- 

 COATED GUINEA PIG 



BLACK -HAIRED, ROUGH - 

 COATED GUINEA PIGS 



INTERCROSSED 



/■ 



y^ 



-X 



9 BLACK -HAIRED, 

 ROUGH -COATED 



3 WHITE HAIRED, 3 BLACK -HAIRED, 1 WHITE HAIRED 

 ROUGH -COATED SMOOTH -COATED SMOOTH -COATED 



Fig. 247.— Results of di-hybridization in guinea pigs which differ with respect 



to color of hair and quality of coat. Black hair is dominant to white hair, and 



rough coat is dominant to smooth coat {cf. Fig. 256). 



Rearrangement of figures from Castle, "Genetics and Eugenics," copyright, 1916, by 

 Harvard University Press, printed by permission.) 



chicks, 50 per cent blue chicks, and 25 per cent white chicks. The 

 black and white offspring breed true, but the blue offspring, 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 is, therefore, in no way different for characteristics that 

 do not exhibit dominance and recessiveness than it is for those in 

 which dominance occurs. In inheritance without dominance, 



