148 



MUTATION. 



Witkuiven in Holland, Mr. Smits, there exists such a case of 

 mutual repulsion in this fowl. Blue females, mated to black 

 males give as many black as blue chicks, but the blues are all 

 females and the blacks are all males. This can be explained 

 only on the assumption that blue is dominant over black, in 

 other words, that the blue colour here is due to the presence of 

 something in addition to the set of genes of the black animals, 

 something which is derived from the white parent. (Fig. 18). 



Fig. 18. 

 Sex-limited colour-inheritance in Witkuiven (Polish). 



We do not think that in the light of the result of further 

 breeding-work with Andalusians, especially of crossing-experi- 

 ments of Andalusians with other breeds, the hypothesis that 

 the three colours are due to homozygosis, heterozygosis and 

 absence of one single gene can be upheld. The dominance of 

 blue over black, which is evident from the sex-linked colour-in- 

 heritance in Witkuiven further proves, that we are dealing 

 with two opposing factors. 



There are cases on record it is true, where heterozygotes 

 could be distinguished from homozygotes. Nilsson Ehle's 



