The morphology and development of ‘ragged’— a mutant affecting the skin and hair of the house mouse I. Adult morphology

Abstract

1. The coats ofRa + mice are sparser than normal;RaRa mice are almost naked. 2. InRa+ mice there is a small proportion of abnormal hairs; mostRaRa hairs are abnormal and not classifiable into the usual types. 3. The proportion of zigzag hairs in the coats ofRa + mice is subnormal, but increases along an antero-posterior gradient. 4. (a) The density of zigzag hairs inRa + mice is subnormal but increases posteriorly, whereas the density of guard hairs and awls tends to be supranormal. (b)Ra+ follicle density is not less than normal, but some follicles do not carry hairs. (c)RaRa follicle density is subnormal: very few follicles carry hairs. 5. (a) Many follicles inRa+ skin and most follicles inRaRa skin are incompletely developed. (b) ManyRa+ andRaRa follicles are curved or abnormally orientated. (c) Adjacent follicles inRa+ skin are often out of phase in their growth cycles. This, and (a), could be the cause of the subnormal increase in skin thickness during follicle growth periods, which, in turn, may produce the abnormalities of follicle shape and orientation. (d)RaRa skin shows periodic hyperplasia of the epidermis, apparently in phases equivalent to normal hair growth cycles. This is interpreted on a theory of competition between skin layers. 6. It is established that most abnormalities in ragged mice, of hair structure and density and of follicle morphology, are more extreme in anterior regions than posteriorly. 7. Observations on the interaction of the Ragged and Naked genes showed that hair cycles occurred inRa+ mice, but were less clearly defined than normal. The assumption that adjacentRa+ follicles were abnormally out of phase was confirmed.