Atp7a^Mo-to, tortoiseshell, semidominant. Arising spontaneously in an obese stock, the tortoiseshell mutation was considered to be a mottled locus allele because of its interaction with other alleles at the locus and because it shows about the same linkage relation with Zic3 (bent tail) as Atp7a^Mo (J:13382). Heterozygous females resemble Atp7a^/+ females in color. The vibrissae are slightly wavy and the coat has a slightly silky texture. The distribution of patches of wild-type and white color is different from the distribution of patches of wild-type and wavy hair, suggesting that Atp7a^Mo-to probably acts independently in melanoblasts and hair follicles (J:15324). Most hemizygous males die before birth (J:24988), but a few are stillborn (J:12963). Using as parent a male presumed to be chimeric for Atp7a^Mo-to/Y and +/Y, Grahn et al. (J:12963) showed that homozygous Atp7a^Mo-to/Atp7a^Mo-to and heterozygous Atp7a^Mo-to/Atp7a^Mo-dp females die in utero, while heterozygous Atp7a^Mo-to/Atp7a^Mo-blo and Atp7a^Mo-to/Atp7a^Mo-br females reach term, but die by 15 days of age. The elastic lamina of the aorta is defective in stillborn hemizygous Atp7a^Mo-to males and in 40 per cent of Atp7a^Mo-to/+ female heterozygotes.