16 



THE GENETIC AND THE OPERATIVE EVIDENCE 



feathered birds. The numbers are too small to be significant, taken by 

 themselves. The expectation for 2 dominants, both essential to hen- 

 feathering, is 1 to 3, and this is in agreement with 2 to 7 as found. 

 It seems, then, more probable from the evidence of the F 2 and of the 

 back-cross combined that there are two dominant factors present in 

 the Sebright that make the male hen-feathered, and since the race 

 breeds true to hen-feathering, both factors must be present in homo- 

 zygous condition unless an undetected lethal destroys some of the 

 classes. 1 



Smith and Haig have reported the following curious case of hen- 

 feathering. Smith had a breed of White Leghorns with cocks of two 

 classes those that assumed cock plumage at 6 months and those 

 that are like the hens for 8 months, after which they slowly assumed 

 the cock-feathering. The difference is hereditary and appears to 

 segregate. Possibly this breed had one factor at least for hen-feathering 

 that is effective for young birds, but not for older ones, or some of the 



1 The expectation for 1 dominant and 1 recessive factor is so nearly the same as for 1 dominant 

 alone that for the numbers obtained no difference between the two cases could be detected. 



