Melanophore Control of the Sexual Dimorphism of Feather Pigmentation Pattern in the Barred Plymouth Rock Fowl *

In two earlier papers21 23 it was reported that when melanoblasts of the Barred Plymouth Rock embryo were grafted into an embryo of a non-barred breed such as the N. H. Red, Black Minorca, and White Leghorn, two definite types of black and white barred patterns were produced in the host contour feathers. The black bands were wider and darker in one type than in the other. These pigmentation differences appeared to be similar to sex-linked differences in barred pattern exhibited in control Barred Rock chicks of the same age. The suggestion was therefore made that the two patterns produced could be accounted for on the basis of sex-linked inheritance of the barring factor, the melanophores from the female donor which has only one gene for barring producing a darker and wider black band in host feather than one from a male donor which has two genes for barring. These preliminary results furnished the basis for the present study on the effects of the sex-linked barring gene upon the melanophores in their control of barred pattern. By introducing melanoblasts from Barred Rocks of known sex by a variety of grafting methods into feathers of the same or of different breeds it has been possible to demonstrate sex-linked differences in the barred pattern produced. The differences in pattern produced by a melanophore with two barring genes and one with a single barring gene may be contrasted and analyzed. When the melanophores of a male genotype and of a female genotype are introduced into either female or male feather germs conditions are provided for distinguishing between the effects of sex hormones and of sex-linked genes in the formation of a sexual dimorphism in feather pigmentation. Another important feature of this study has been a comparison of the barred