Coat color genetics of Peromyscus: IV. Variable white, a new dominant mutation in the deer mouse.

The variable white mutation arose spontaneously in 1983 within a laboratory stock of wild-type deer mice (Peromyscus maniculatus). The original mutant animal was born to a wild-type pair that had previously produced several entirely wild-type litters. Other variable white animals were bred from the initial individual. Variable white deer mice exhibit extensive areas of white on the head, sides, and tail. Usually a portion of pigmented pelage occurs dorsally and on the shoulders, but the extent of white varies from nearly all white to patches of white on the muzzle, tip of tail, and sides. The pattern is irregular, but not entirely asymmetrical. Eyes are pigmented, but histologically reveal a decrease in thickness and pigmentation of the choroid layer. Many variable white animals do not respond to auditory stimuli, an effect that is particularly evident in animals in which the head is entirely white. Ataxic behavior is also prevalent. Pigment distribution, together with auditory and retinal deficiencies, suggests a neural crest cell migration defect. Breeding data are consistent with an autosomal semidominant, lethal mode of inheritance. The trait differs from two somewhat similar variants in Peromyscus: from dominant spot (S) in extent and pattern of pigmentation and from whiteside (ws), an autosomal recessive trait, in the mode of inheritance and viability. Evidence for possible homology with the Va (varitint-waddler) locus in house mouse (Mus) is presented. The symbol Vw is tentatively assigned for the variable white locus in Peromyscus.