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]
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 birds pass through a stage when they produce an internal secretion that disappears later. But it is also possible, and perhaps more probable, that the young birds, not cock-feathered, have remained longer in the juvenile stage than the others, so that they might be said to be falsely hen-feathered.
The results published by the Rev. E. Lewis Jones in 1914, describing crosses between two breeds of Campines, one called Belgian (which has hen-feathered males), the other English (that has cock-feathered males), are summarized in the table on page 16. They show the dominance of hen-feathering with some probability. The table given there is the original, to which the author has kindly added the numbers here prefixed to some of the classes. The numbers are not large enough in all cases to be satisfactory, but the dominance of the hen-feathering is, I think, apparent, as well as its non-sex-linked transmission. The golden female in C must have been English type, or at any rate heterozygous for English-type feathering, for if Belgian her sons would have been Belgian type.
Punnett and Bailey (1914) have published the result of a cross with hen-feathered Silver Sebrights and Hamburgs. The dominance of hen-feathering in the male is shown in the figures that illustrate their paper, but as the paper deals solely with the inheritance of weight the account of inheritance of hen-feathering was deferred to a later paper, that has not yet appeared.
HEREDITY OF COLOR IN THE CROSS BETWEEN SEBRIGHT AND BLACK-BREASTED GAME BANTAM.
The cross between the Sebright and the Black-Breasted Game bantam was undertaken primarily to study the inheritance of hen-feathering. The Sebright was chosen, on the one hand, because this race is pure for hen-feathering, whereas in other races, such as the Campines, both kinds of males are known. The hen-feathered birds of such races are, I believe, frequently not pure for hen-feathering. The game race was chosen because the cock has the typical plumage of the wild bird, Gallus bankiva, and although his feathers are remarkably short, they show the characteristic cock-feathered type.
Only secondarily was the experiment concerned with color inheritance. The two breeds differ so markedly in coloration and pattern that the very complex results that appeared in F₂ were to be expected. In addition to the differences involving hen-feathering versus cock-feathering, and Sebright plumage versus game plumage, the game is strongly dimorphic in the plumage, while in the Sebright the coloration of the two sexes is closely similar. But the castration experiments have shown that this difference is the result of hen-feathering in the Sebright cock, and that the race carries the same potential dimorphism as do other races of poultry.
The game cock is shown in [plate 1], figure 1, and [plate 4], figure 1. The wattles and comb had been removed from the bird. The yellow-red back and saddle are to be noted. The upper tail coverts and sickle feathers are black, as is the tail. These parts are shorter in the game than in other races, being one of the points selected for. The dorso-anterior edge of the wing is black, this color meeting across the middle of the back. Below this black area comes the red wing bow, followed by a double row of blue-black feathers. The exposed portions of the secondaries are brown, of the primaries black with green margin. The breast and entire lower surface is black. The legs are greenish, the bill black and yellow, the iris yellow.