A presumed deletion covering the W and Ph loci of the mouse.

A new allele at the >F-locus (W), found in a mutagenesis experiment in which females were irradiated, involves a presumed deletion. The deletion covers the Ph locus (which forms part of a gene complex with the W, Ph and Rw loci), and the locus of a recessive lethal 2 cM distal to W. It does not extend distally to the bl locus; nor does it involve the Rw locus, W/Rw compounds being viable and fertile. Thus, the length of the deletion is 2-7 cM. The non-involvement of Rw shows that, in the gene triplet Rw, W, Ph, Rw must lie proximal to J^and Ph, whose relative position remains unknown. Heterozygotes for W" are not anaemic, show only minimal white spotting and no pigment dilution; they thus resemble heterozygotes for the original W mutant allele and differ from W/Ph trans heterozygotes, which have extensive white spotting. In addition W heterozygotes may be small and runted, many are believed to die prenatally, and some in the nest. Their radiosensitivity is increased. Homozygotes die at the pre-implantation stage.