22 



THE GENETIC AND THE OPERATIVE EVIDENCE 



feathered males, i. e., their class relationship can only be determined 

 for the classes that resemble the F x and the Pi birds. The F 2 hen- 

 feathered males can in part be further identified by means of the 

 evidence that castration of these types affords. 



Two of the F 2 classes of hens can be identified in this back-cross, 

 viz, (a) 4 hens like the Fi birds, (6) 3 hens like the game; (c) there were 

 3 other hens with plain yellow, i. e., not stippled backs. The upper 

 surface was like that of the game female, but much lighter. The first 

 two classes (a), (b) might be again split into two types. There were 

 only two hen-feathered males, one nearly like the Fi male, the other 

 blacker; they probably belong to different classes. 



Of the 7 cock-feathered males, one was like the Fi castrated males; 

 another had a similar back, but a darker and differently marked 

 breast; 2 were game-cock type; 3 were odd birds much like the game 

 cock above except for absence of black, with reddish heads without any 

 black. The males may be approximately classified as follows : 



Four or five types may then be recognized in this rough grouping. 

 None of the groups seem uniform and probably might be split again. 



D. The Number of Color Factors Involved. 



The theoretical expectation for two pairs of factors calls for 4 classes 

 in the back-cross, but this assumes that the parent type used for back- 

 crossing contains all (here 2) recessives. But this simple assumption 

 can not be true in this case, for the F x bird would have been like the 

 Sebright. On the 3-factor assumption the expectation for the back- 

 cross is 8 classes, but this would apply only if the game were the triple- 

 recessive form, which, again, it is not, as shown by the F] cross. But if 

 the dominance of one or more of the Sebright color factors is incomplete, 

 then either a 2 or 3 factor assumption might apply to the back-cross. 



If only 2 pairs of factors are present we should expect to recover the 

 game type once in 16 cases in F 2 . But, as will be shown, only 1 game 

 was recovered out of the 49 F 2 females. This result fits better with a 

 3-factor assumption, for even with the small number in the back-cross 

 the indications are that more than 4 classes are present. 



