Inheritance of Characteristics in Domestic Fowl

by Charles Benedict Davenport

The correspondence is certainly close. The hypothesis of factors thus receives additional support and the variability of the offspring in the second hybrid generation is sufficiently explained.

4. WHITE LEGHORN × BLACK MINORCA.

As we have already seen, the gametic formula of the White Leghorn is CJNWx and that of the Minorca is CJNwx, so that the F₁ generation has the zygotic formula C₂J₂N₂Wwx₂ or, more simply, C₂J₂N₂Ww. These heterozygotes are white because of the graying factor, but, as this factor is diluted, some black shows, particularly in the females. In F₂, on account of there being only 1 heterozygous factor, only 3 kinds of zygotes are formed, C₂J₂N₂W₂, C₂J₂N₂Ww, and C₂J₂N₂w₂, in the proportions 1: 2: 1. Since not only offspring homozygous in W, but also all male heterozygotes, are white and many female heterozygotes are late in revealing any pigment, it is necessary to consider together individuals homozygous and heterozygous in W. Consequently we may expect 75 per cent of the offspring to show white or white-black-speckled plumage, and 25 per cent black or black and white like the young Minorca. Actually, in 154 offspring (pen 633) I obtained 116 white + white-black + blue, and 38 black with more or less white and including 4 barred, of which more later. Expectation is 115.5 and 38.5, respectively.

In another experiment I crossed the F₁ hybrids on a pure White Leghorn and got 41 offspring, all white except 1 that showed some black specks. All results thus accord with hypothesis.

5. WHITE LEGHORN × BUFF COCHIN.
([Plate 9].)

These two races afford the gametic formulæ CJNWx and CjnwX, respectively. The F₁ hybrids consequently have the zygotic formula C₂JjNnWwXx. Such hybrids are heterozygous in all factors except C. Such complex heterozygotism, combined with the well-known sex differences in color of heterozygotes, leads to a very great diversity of the offspring. As a matter of fact I found, as Hurst did, that the young were sometimes quite white, sometimes white and buff, and sometimes showed also a little black. Since there are 4 heterozygous characters, there are 256 possible combinations of them, which reduce to 81 different kinds of combinations. Owing to the ambiguous nature of the soma in many of the heterozygotes and to the relatively small number of offspring, it is useless to compare theoretical and observed distributions of plumage colors in the somas. Suffice it to say that white, buff, black, and Game-colored chicks all appeared in the F₂ generation, as well as some with a mixture of colors, as called for by the hypothesis. White, due to the powerful graying factor, was the commonest color, buff and black were about equally common, and each about one-third as abundant as white, while Games, due to the hypostatic J factor, were about one-third as common as buff. All this, again, is explicable upon our hypothesis and upon none other so far proposed. In mating the F₂ generation with each other or with the White Leghorn the result must vary with the gametic output of the hybrid, which is obviously very different in different cases. A hen, of a light buff color spangled with white spots and having a black tail, presumably formed gametes CJnWX, CJnwX, CJNWX, CJNwX. Mated with the White Leghorn, CJNWx, she produced 8 pure whites, 4 whites with some black and red, 2 buff and white, and 3 black with trace of white. Expectation in 16 offspring would be about 4 pure whites, 4 white mixed with pigment, 4 buffs with white (and black?), and 4 blacks mixed with other colors. This is merely an illustration of the way the confused combinations of colors become intelligible, and even necessary on the factor hypothesis.

6. BLACK COCHIN × BUFF COCHIN.
([Plate 10].)

The factors involved in this cross seem to be CINx for the Black Cochin (in which I stands for the Jungle pattern without any associated color factor) and CjnX for the Buff Cochin, as before. The F₁ generation has the zygotic composition C₂IjNnXx, and the females are all black, except for a variable amount of red on the hackle, and the males are black and red, like Games. The F₂ generation is remarkable. Since 3 factors are heterozygous, there are 64 possible combinations and 27 differing ones. In table 63 is given a list of these different combinations and of the probable associated somatic colors. The prefixed number indicates the frequency of each combination.

Table 63.

1 C2I2N2X2 Black.	2 C2IiN2X2 Black.	1 C2i2N2X2 Black.
2 C2I2N2Xx Black.	4 C2IiN2Xx Black.	2 C2i2N2Xx Black.
1 C2I2N2x2 Black.	2 C2IiN2x2 Black.	1 C2i2N2x2 Black.
2 C2I2NnX2 Black and red.	4 C2IiNnX2 Black and red.	2 C2i2NnX2 Black and red.
4 C2I2NnXx Black.	8 C2IiNnXx Black.	4 C2i2NnXx Black.
2 C2I2Nnx2 Black.	4 C2IiNnx2 Black.	2 C2i2Nnx2 Black.
1 C2I2n2X2 Buff.	2 C2Iin2X2 Buff.	1 C2i2n2X2 Buff.
2 C2I2n2Xx Buff.	4 C2Iin2Xx Buff.	2 C2i2n2Xx Buff.
1 C2I2n2x2 White.	2 C2Iin2x2 White.	1 C2i2n2x2 White.