208 Bulletin No. 155. — 1913. 



added to the barred pattern possessed as a eryptomere by the W. P. R. 

 breed, the barring appears, we are forced to the conclusion that this 

 breed does not normally carry this factor for black pigmentation but 

 that the character lies dormant in the W. L. stock reappearing when 

 it is freed from its inhibitor 7. The fact that no black individuals, 

 o^c^ or 99, but only barred (and white) birds arose fromi this 

 cross in F2 is additional proof of the homozygous condition of the 

 W. L. d^ with respect to the factor for barred plumage pattern. 



There may be, however, one other possible explanation of the 

 appearance of black-pigmented feathers in Fi birds and a certain 

 proportion (6 in 32) of barred individuals in Fo. It is conceivable 

 that the W. L. d^ and the W. P. R. 9 each contain one of the factors 

 whose fusion is necessary for the full manifestation of black pig- 

 mentation. Bateson and Punnett {op. cit.) have described a case in 

 which the mating together of two R-whites produced progem- all of 

 which were dark colored. These factors may be designated .Y and Y 

 and it may be assumed that, while neither alone can determine black 

 pigmentation, X and Y working together {i. e., XY) are able to bring 

 it about. In case the W. L. cf was homozygous for the factor X, 

 and the W. P. R. 9 homozygous for the factor Y, all the offspring 

 would be AT, — compatible with black pigmentation. But upon the 

 assumption that the W. L. d^ is h, this pigment would not be mani- 

 fested in the Fi individuals. Making use of this hypothesis the 

 W. L. cf would be 82/212X21/2 forming gametes 



BflXij • DflXij 

 while the W. P. R. 99, having the zygotic constitution BbFfu^XiY^j 

 would form gametes 



BfixY ' hFixY 

 The mating would then be expressed: 



d^ BfIXy • BilXy X 

 9 BfixY ' hFixY — 



d^ & B2f2liXxYy, white 

 99 BhFfliXxYy, white 

 All of the Fi individuals are heterozygous for /, X and Y. The 



