EELATING TO SECONDARY SEXUAL CHARACTERS 



15 



ing been retained in the oviduct of the female during her isolation 

 period. In the second edition published a few months later the mis- 

 take, having been found out, was corrected. 



If one dominant suffices to produce hen-feathering, the Fj ratio 

 would be 3 hen-feathered to 1 cock-feathered bird. The numbers 

 found were 31 to 28. This realized ratio departs too far from a 3: 1 

 ratio to make it probable that the results are due to a single factor. 



The Fa expectation for two dominants, both necessarily present to 

 produce hen-feathering, is 9 hen-feathered to 7 cock-feathered birds. 

 If the dominant factors are represented by H and H' and their wild- 

 tjrpe (recessive) allelomorphs by h and h', the expected F2 recombina- 

 tions are given in the following table: 



There are 9 classes containing both H and H', 6 containing one or 

 the other, and one containing neither H nor H'. The realized numbers, 

 31 to 28, are in close approximation to 9: 7. 



In classifying the F2 hen-feathered males, an attempt was naade to 

 divide them into two classes, viz, type 1, hen-feathered to the same 

 extent as the Sebright, and type 2, intermediate between hen and cock 

 feathering. The line between intermediate and cock-feathering is 

 sharp, all the intermediates belonging distinctly to the hen-feathered 

 group, but the Une between the two subdivisions of hen-feathered 

 birds is not sharp, and occasionally a bird is found that is difficult to 

 place. These statements hold also for the Fi birds, whose skins I now 

 have. Five of these are classified as intermediates and one as com- 

 pletely hen-feathered. The difference between these two classes, then, 

 is environmental or due to other modifying genetic factors, for which 

 either the Sebright or the game is not pure. Under these circumstances 

 it would not be profitable to attempt to find out (without additional 

 evidence) what genetic differences, if any, he behind the hen-feath- 

 ered and intermediate-feathered birds in the F2 classes. 



Concerning the back-cross (Fj by game) the expectation, for one 

 dominant factor-difference, is 1 hen-feathered to 1 cock-feathered 

 male. There were obtained 2 hen-feathered (intermediates) to 7 cock- 



