358 MR. J. T. CUNNINGHAM ON 



We may suppose that the mating of the F„'s may be represented 

 thus : — 



Group A XYXYS x XYXY8. 



Group B XYYxS X XYyXS. 



Group A, gametes... XYS f XY x XYS + XY. 



F3 XYXYSS + XYXYS + XYXY8+XYXY^ 



The first should be pure white dominants, the next two typical 

 piles, and the last recessive black-red, the suppressing factor 

 being absent. 



Group B, gametes. . . XYS + xYS + XY + xY x XYS + XyS + 



XY + Xy. 

 F„ XXYYSS, XXYySS, xX YYSS, xXy Y^SS. 



2XXYYS, 2XXYyS, 2XxY^YS, 2xXyYS. 



XYXY, xYXY, XYXy, xXyY. 



Thus there would be four combinations of Xx and Yy. namely 



XXY^Y, XXYy, XxYY, and xXy Y ; 



and these would be combined with SS, S, or absence of S. There 

 would be, therefore, in 16 individuals four coloured recessives of 

 varying composition, four pure dominants, and eight heterozygotes 

 or piles. This agrees fairly well with my results, if we assume 

 that the different combinations of the colour components affect 

 the degree of visible colour. 



It is evident, however, that the combinations which are 

 recessive for S ought to show no more white than did the 

 original Black red, whereas in my specimens the three lecessive 

 hens show distinct evidence of white : this is more in accordance 

 with the assumption of imperfect segregation. 



In the second cross the hens with most white and least colour 

 were mated with anothei- black-red. If we suppose that the 

 white hens had more of the colour factors than the original 

 Whites and were of constitution XYXYSS, then the cross would 

 be 



XYXYSS X XYXY. 



Gametes XYS and XY. 



Progeny XYXYS. 



Thus all the piles in this case will be homozygous for the 

 combination XY, whereas in the first cross many of the piles were 

 heterozygotes for this combination. 



Lastly we may consider the possible genetic combinations in 

 the fancier's pi-ocess of crossing pile with black-red to improve the 

 colour of the former. The cross might be 



XYXYS X XYXY. 



Gametes XYS + XY x XY, 



Progeny XYXYS + XYXY. 



