' Matted ' , a New Hair - mutant in the House - mouse : Genetics and Morphology

T H R E E types of hereditary hairlessness are known in the house-mouse. With Naked (Fraser, 1946) and Alopecia (Dickie, 1955), baldness results from the breaking of hairs; with hairless and its allele rhino, from the shedding of entire hairs (Fraser, 1946). The crinkled (Falconer, Fraser, & King, 1951) and ragged (Carter & Phillips, 1954) genes, however, lead to a complete absence of certain hair-types, due to delayed or imperfect follicle development (agenesis). In rough (Falconer & Snell, 1952) the fur is greasy and looks unkempt but no baldness occurs. Matted, the new mutant to be described in this paper, belongs to the first of these three categories. The degree of baldness varies greatly; there may be no signs of any hair loss, or a complete absence of fur over the back and flanks. The head and belly are not affected as a rule. The more extreme manifestation is associated particularly with the later stages of each coat generation. Whatever coat is present it looks and feels rough, in sharp contrast to the sleekness of the normal mouse. Instead of lying down flat against the body, the mutant's hairs tend to stand up as if inflexible and stick together at the tips so as to form matted clumps; a very characteristic feature (Plate, figs. A, B. C). In agouti mice this erection of the hair causes a darkening of coat colour, for the black basal part of each agouti hair becomes visible. The present paper deals with the genetics of the new mutant and explains its effect in terms of the underlying abnormalities of hair structure. A paper by Jarrett & Spearman (1957) deals with finer structure and the results of chemical and physical studies.