The F₂ 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-type (recessive) allelomorphs by h and h´, the expected F₂ recombinations are given in the following table: +-----+-----+-----+-----+-----+ | | HH´ | Hh´ | hH´ | hh | +-----+-----+-----+-----+-----+ | HH´ |{HH´ | Hh´ | hH´ | hh | | |{HH´ | HH´ | HH´ | HH´ | | +-----+-----+-----+-----+ | Hh´ |{HH´ | Hh´ | hH´ | hh | | |{Hh´ | Hh´ | Hh´ | Hh´ | | +-----+-----+-----+-----+ | hH´ |{HH´ | Hh´ | hH´ | hh | | |{hH´ | hH´ | hH´ | hH´ | | +-----+-----+-----+-----+ | hh |{HH´ | Hh´ | hH´ | hh | | |{hh | hh | hh | hh | +-----+-----+-----+-----+-----+ 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 made 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 line 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 F₁ birds, whose skins I now have. Five of these are classified as intermediates and one as completely 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, lie behind the hen-feathered and intermediate-feathered birds in the F₂ classes. Concerning the back-cross (F₁ 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-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 F₂ 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 homozygous condition unless an undetected lethal destroys some of the classes.[1]