The Tyrp1^b-11R30M mutation was identified in the progeny of a (101/Rl x C3H/Rl)F1 male exposed to a 0.3 Gy dose from a neutron source then bred immediately to a female from T stock, a non-inbred strain that was homozygous for seven recessive alleles, a, Tyrp^b, Tyr^c-ch, Oca2^p, Myo5a^d, Bmp5^se, and Ednrb^s. It is likely that there were several subsequent crosses to (101/Rl x C3H/Rl)F1 during which the new mutation was characterized as causing prenatal lethality in the homozygous state. The Tyrp1^b-11R30M deletion, which includes Whrn, was imported from Oak Ridge National Laboratory into the laboratory of Dr. Jane Barker at The Jackson Laboratory. It was maintained in a 2 generation breeding scheme starting with a cross of Tyrp1^b/Tyrp1^b-11R30M compound heterozgyotes to C3H/HeJ then test crossing the offspring to B6.Cg-Whrn^wi Tyrp1^b/+ +/J to identify mice carrying Tyrp1^b-11R30M, not Tyrp1^b. These were then bred to brown mice (Tyrp1^b/Tyrp1^b) from a population of (C57BL/6J x DBA/2J)F2 mice to again obtain Tyrp1^b/Tyrp1^b-11R30M compound heterozgyotes. Currently the Tyrp1^b allele can be detected by genotyping. Embryos were cryopreserved from Tyrp1^b/Tyrp1^b-11R30M compound heterozygous males bred to C3H/HeJ females and the cryo-recovered pups that do not carry Tyrp1^b are presumed heterozygous for Tyrp1^b-11R30M.