‘Bare’, a new hairless mutant in the mouse—genetics and histology

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Abstract
1. A new hereditary defect affecting the hair coat of Swiss albino mice is described. The defect was found to be inherited as a recessive character and is designated as bare (ba).2. The gene affected the vibrissae as well as pelage hairs. The lack of vibrissae and other sensory hairs at birth, helped to differentiate them easily from the normal animals. The first hairs on the body appeared at 13–14 days of age. The hairs were thin and tiny and remained there till about the thirtieth day. The hairs in the second hair cycle appeared at about 45 days, and again disappeared within 10 days. The animals were entirely naked when they were 6 months old.3. Gross as well as microscopic examination of hairs in the first hair cycle did not show the four different normal types of hairs. The hairs were comparatively very small, thin, and the internal structure did not show any regularity in the arrangement of the air cells.4. No difference was found in the number of hair follicles in the bare and the normal Swiss mice.5. Histology revealed the presence of keratinized globular masses instead of straight hair. This abnormality persisted in all the hair cycles.6. The bare mice were compared with the other mutants and placed in the Alopecia-Naked group where the abnormality was in the keratinization of the hair.