Oca2p-25H/Oca2p-25H mice exhibit significant dilution of coat color with pink eyes, similar in appearance to Oca2p/Oca2p mice. The Oca2p-25H phenotype also includes a slightly jerky gait with some tremor, small body size compared to control littermates, male sterility, female semisterility, and impaired maternal behavior, and the smaller-than-expected proportion of Oca2p-25H homozygous intercross offspring implies reduced prenatal viability (Lyon et al. 1992, Phillips et al. 1977). The Oca2p-25H mutation comprises an inversion of a segment of Chromsome 7 that alters the 5' end of the Oca2p gene so that no detectable ptranscript is produced, accounting for the pigment-dilution phenotype (Gardner et al. 1992). The deletion also disrupts the Herc2/rjs gene proximal to Oca2p so the transcript sequence diverges from wild-type after the first 8772 bp (of 15 kb in wild-type), resulting in a truncated protein and accounting for the non-pigment related aspects of the Oca2p-25H phenotype (Lehman et al. 1998). Mice homozygous for Oca2p-d are born with lightly pigmented eyes, darker than those of Oca2p/Oca2p mice, which darken by weaning and a coat color "considerably darkerthan that of Oca2p/Oca2p mice, somewhat resembling that of brown [Tyrp1b/Tyrp1b] mice"; both sexes are fertile (Gardner et al. 1977, Lyon et al. 1992). A normal-sized Oca2p transcript is present in eyes of Oca2p-d/Oca2p-d mice (Gardner et al. 1992), and Southern blot analysis revealed no gross alteration of the Oca2p gene (Gardner et al. 1992, Lyon et al. 1992); thus, the molecular nature of the defect is unknown. Oca2p-d/Oca2p-25H compound heterozygotes have a color phenotype intermediate between those of the two homozygotes: eyes are "lighter at birth than those of Oca2p-d/Oca2p-d mice (but not as light as those of Oca2p/Oca2p mice) and darken by weaning"; ears and tail are lighter than those of Oca2p-d/Oca2p-d mice, but coat color is indistinguishable. The compound heterozygotes exhibit no behavioral abnormalities and are fertile (Lyon et al. 1992).
