Developmental Morphology of the Skin and Hair Follicles in Normal and in “Ragged” Mice

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Abstract
Ragged (Ra) is a semi-dominant mutant gene which was first reported by Carter & Phillips (1954). The adult morphology, the genetics, and the embryology of the mutant mice were described by Slee (1957 a, b). It was found that adult ragged heterozygotes (Ra+) had sparser coats than normal, many of their hair follicles being incompletely developed and non-functional. Ragged homozygotes (RaRa) were almost naked. Most of their pelage hair follicles were either absent, or abnormal and non-functional. Ra+ embryos could be identified from 16 days’ gestation by the retardation of their sinus hair-growth. RaRa embryos were characterized from 13 days’ gestation by the occurrence of a generalized subcutaneous oedema which persisted until birth, and also by retardation in the development of their sinus hairs and follicles. Pelage follicle primordia appeared at the normal time (14 days’ gestation) in Ra+ and RaRa embryos but subsequently developed slowly in RaRa embryos, especially when the oedema was pronounced.