MENDELIAN EXPERIMENTS ON FOWLS. 357 



In the second cross with G. hankiva S the F,, hens with least 

 colour wei^e used, and, as mentioned above, the offspring were all 

 pile, i, e. showed more pronounced coloration to a more uniform 

 degree in the difl'erent individuals. It may be suggested that this 

 was due to mating with a black-red of difierent race, but I think 

 it shows that the F„ white hens had more colour in their heredity 

 than the original White Leghoin hens. On the other hand, the 

 genetics may be more complicated than merely the meeting of a 

 single pair of allelomorphs, dominant white and black-red. 

 Bateson in 1909 concluded from his own breeding experiments 

 that the black-red coloui' was due to two complementary factors 

 X and Y, and that the dominant white of White Leghorn was 

 due to a suppressing factor S for which birds of that breed are 

 homozygous. One or both colour factors may be present in the 

 White Leghorn, but even when both are present, colour is 

 suppressed by the factor S. 



Some dominant white are of the genetic constitution Xx Yy 

 SS : the factors of the Black-red Game may be assumed to be 

 XXYY. My cross will then be :— 



Xx Yy SS X XXYY. 



Gametes YXS, YxS, yXS, yxS x XY. 



F, XYXYS, XYYxS, XYyXS, XYyxS. 



All these combinations contain both factors for colour, i. e. XY, 

 and all contain only one suppressing factor S. This would help 

 to explain why in F^ colour is not entirely suppressed, but it 

 does not explain why the black is suppressed more than the 

 red. It would also help to explain why the degree of coloration 

 is different in the F^ birds, for in one combination both X and Y 

 are double, while in the other three XY together are present only 

 once, with either an additional X. an additional Y, or neither. 

 The birds of constitution XYXYiS then may be the typical piles, 

 and the others the palest cocks and white hens of F^. The 

 difference, however, was not sharply marked. 



Again, one or both of the White Leghorn hens in my first cross 

 may have been XxyyS. In this case the cross could be analysed 

 thus : — ■ 



XxyyS>S X XXYY. 



Gametes XyS, xyS x XY. 



F^ XYXyS, XYxyS. 



There would be only two combinations, and each would have 

 the compound XY only once, or in the simplex condition as in the 

 two last combinations in the former case. There would probably 

 then be no typical or deeply coloured piles. It is more probable, 

 therefore, that in my cross the constitution of the hens was 

 XxYySS. I do not know whether a White Leghorn of consti- 

 tution XYXYSS could occur, and therefore will not consider it 

 here. 



