Dominant Spot (S)
ALLELES:, S (mutant), S+ (wild-type).
INHERITANCE: Dominant. Variable expression.
PHENOTYPE: Deer mice carrying this mutation typically have a white spot on the center of the forehead. The distal portion of the tail is unpigmented, and extensive areas of all-white hair occur on the ventrum. Hairs in the spotted areas lack pigment entirely. This trait is variably expressed and spotting may include the face, neck and chest. White spotting centers on the midline, but asymmetry occurs in many individuals. The dorso-ventral color discontinuity is more irregular than in the wild type.
SOURCE: About 1928. Two wild P.m. bairdii trapped from near Morrison IL, showed the trait. Mutant progeny were subsequently maintained at the University of Michigan.
REFERENCE: Feldman (1936), Maddock (1966).