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Bateson's explanation is that the female, according to the Mendelian theory of sex, is heterozygous in sex, the male homozygous and recessive, and that lacticolor is linked with the female sex-character, grossulariata being repelled by that character. Thus we have, the lacticolor character being recessive,
The more important question is whether distinct stages can be caused by mutation. It is true that in heterozygous individuals characters may develop more fully in the adult stage than in the young. But when we find different stages evidently adapted to different modes of life, it is impossible to explain them by mutations affecting different stages of life.
In Mendelian language the male is homozygous, so-called "pure" as regards this character. But the female is heterozygous, "impure" in the sense that her femaleness depends upon the dominance of the factor for femaleness over the factor for maleness, which also is present in her. In the Mendelian terminology, she is an instance of impure dominance.
The plumage is an epidermic structure, and therefore distinct from the connective tissue, but it is difficult to understand why a pigment factor though present in every cell has no effect on epidermic cells. The Mendelians, when the mutations of Oenothera were first described, endeavoured to show that they were merely examples of the segregation of factors from a heterozygous combination.
As mentioned above, he argues from the fact that injury or disease of the ovaries may lead to the development of male characters in the female, that the female is heterozygous for sex, and from the supposed fact that castration of the male leads merely to the non-appearance of male somatic characters, that the female sex-factor is wanting in the male.
That is all offspring normal, but the males again heterozygous. An affected male has the constitution nn, and if he marries a normal woman the descent is as follows: When a normal male is mated with a heterozygous nN female we get that is, half the sons are normal and half colour-blind, while half the females are homozygous and normal, and the other half heterozygous and normal.
One example in the barred character of the feathers in the breed of fowls called Plymouth Rock. In this the female is heterozygous for sex as in Abraxas grossulariata, and the barred character is sex-linked. When a barred hen is crossed with an unbarred cock all the male offspring are barred, all the females plain.
This was supposed to support the view that the male is homozygous in sex, the female heterozygous in Vertebrates: that is to say, the female sex-character and the female secondary sex-characters are entirely wanting in the male.
In the next generation m in the male would be affected, and the male for the sake of simplicity might be supposed to become MMXX. When the female gametes segregated, some would always be mY, and some zygotes therefore MXmY. Others might be MMXY. On this theory, therefore, there would always be some females heterozygous for the male character.
Homozygous. B male B male X b female b male B male b female b male b male Barred female. Barred male. Heterozygous. This case is thus exactly similar to that of Abraxas grossulariata and A. lacticolor.
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