Hormones and heredity; a discussion of the evolution of adaptations and the evolution of species; . Barred Barred This case is thus exactly similar to that of Abraxasgrossulariata and A, lacticolor. The barred character,like grossulariata, is dominant, the unbarred recessive,and to explain the results it is necessary to assumethat the female is not only heterozygous for thebarred character, but also for sex, with the femalesex-factor dominant. The recessive character inthis case is linked to the female sex-chromosome,or, as Bateson described it, the domi
Hormones and heredity; a discussion of the evolution of adaptations and the evolution of species; . Barred Barred This case is thus exactly similar to that of Abraxasgrossulariata and A, lacticolor. The barred character,like grossulariata, is dominant, the unbarred recessive,and to explain the results it is necessary to assumethat the female is not only heterozygous for thebarred character, but also for sex, with the femalesex-factor dominant. The recessive character inthis case is linked to the female sex-chromosome,or, as Bateson described it, the dominant character isrepelled by the female sex-factor. We may make adiagram of the kind given by Morgan if we use arod of different shape for the female-producing sex- SEX-CHARACTERS IN EVOLUTION 117 chromosome, and use the black rod for the dominantcharacter:— 10 BARRED (5 Heterozygous. UNBARRED Cj 00. 0 UA/BARRED Q Homozygous. BARRED Q Heterozygous. Another case is that of tortoise-sliell, i,e, blackand yellow cats. The tortoise-shell with very rareexceptions is female, the corresponding male beingyellow, without any black colour. Doncaster foundthat a yellow male mated to a black female producedblack male offspring and tortoise-shell females. 118 ORIGIN OF SOMATIC When a black male is mated to a yellow female, thefemale kittens are tortoise-shell as before, but themales yellow. The Mendelian hypothesis whichexplains these results is that the male is alwa^^sheterozygous, or has only one colour factor whetheryellow or black, and transmits these colours onlyto his daughters, while the female has twocolour factors, either BB, YY, or BY, Thus thecrosses are:— yocS
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