THE EXPRESSION AND INTERACTION OF HEREDITARY FACTORS AFFECTING HAIR GROWTH IN MICE: EXTERNAL OBSERVATIONS

Abstract

Macroscopic observations on the expression of two mutant alleles ("hairless" and "rhino") in the house mouse, and on their interaction with one another and with a third mutation ("Naked") producing hypotrichosis of a different type, have been described. In hairless mice the juvenile pelage falls out and the skin shows little wrinkling; rhino mice lose their hair in a similar way but subsequently develop an intense wrinkling of the skin. Naked mice lose their hair by a breaking-off rather than a falling out, and show a pattern of alternate depilation and regeneration of the hair coat.Hairless/rhino hybrids lose their hair according to the hairless pattern, but later manifest a characteristic wrinkling like, but not as extreme as, that of the rhino mutant, "rhino" is therefore not completely recessive to "hairless."There are thus three basic grades of wrinkling—hr/hr, hr/hr^rh, hr^rh/hr^rh—determined by the factors present at the Hr locus. The presence of the heterozygous Naked factor in any of these types causes an intensification of its degree of wrinkling. This intensification is even more pronounced when the Naked factor is homozygous. Moreover, the "Naked" characteristics are themselves exaggerated in these compounds, the intensification being proportional to the degree of wrinkling.These results will be interpreted in the light of histological findings to be presented in the following paper.