Studies of Heredity

Abstract

MR. C. C. LITTLE has studied (Journal of Genetics, vol. viii., 1919, pp. 279-90) colour inheritance in cats, with special reference to black, yellow, and tortoiseshell, and gives an explanation- not a very easy one—of the rare occurrence of tortoise-shell males which may be either sterile or fertile. The genetic constitution of the normal colour varieties of cats as regards yellow and black pigmentation appears to be as follows: B = a factor producing black pigmentation, Y = a factor which restricts black from the coat, and y=a factor allelomorphic to Y and hypostatic to it, allowing black pigment to extend to the coat. Mr. Little also discusses (Science, vol. li., 1920, pp. 467-68) a curious case in the Japanese waltzing mouse of hereditary susceptibility to a transplant-able tumour. He concludes provisionally that from three to five factors—probably four—are involved in determining susceptibility to the mouse sarcoma; that for susceptibility the simultaneous presence of these factors is necessary; that none of these factors is carried in the sex (x) chromosome; and that these factors Mendelise independently of one another. In another paper (Amer. Naturalist, vol. liv., 1920, pp. 267-70) the same investigator criticises Dunn's suggestion that there is a linkage between the genes for yellow and for black in mice, and shows that the facts may be explained by assuming that yellow, when present, hampers the action of a lethal factor in much the same sort of way that it hampers the activity of the black-forming factor in the skin and hair. In a note on “Some Factors Influencing the Human Sex-Ratio” (Proc. Soc. Exper. Biol. and Medicine, vol. xvi., 1919, pp. 127-30) Mr. Little concludes: (1) That a significant excess of males is observed in the progeny of human matings involving racial crosses as compared with matings within the race; (2) that racial crosses between the European races studied (Italian and Spanish) will produce in the first hybrid generation a significant excess of males (which will be economically important to the United States); and (3) that there are significantly fewer stillbirths among the progeny of the hybrid matings studied than among the pure matings. In another paper (Amer. Naturalist, vol. liv., 1920, pp. 162-75) Mr. Little deals with exceptional colour-classes in doves and canaries. These have been explained on the hypotheses of “partial sex-linkage” and “non-disjunction,” but the author thinks it is more legitimate to suppose a factorial change from one gene to its allelomorph, perhaps as the effect of “intergenic and intra-cellular environment.” In a note on the origin of piebald spotting in dogs (Journal of Heredity, vol. xi., 1920, pp. 1-4, 3 figs.) Mr. Little deals with two cases in dogs which give direct evidence as to the origin of spotted individuals, and suggests that a spotted race may arise from a self-race, by mutation, without passing through a series of minute gradations directed by selection.