Chapter 8

X-Linked Determinants

III. Yellow Mottling ( Ym) and Pewter ( Pew)

The only other X-linked coat-color determinants are yellow mottling ( Ym) and pewter ( Pew). Ym arose in an experiment at Oak Ridge in which (101 x C3H)F₁ males received a partial body exposure of 500 R acute X-ray and, 24 hours later, an additional 100 R. These males were mated to females homozygous for seven recessives and scored for mutations. An F₁ male from this cross produced a single Ym/+ daughter out of a large number of progeny. Hence it appears that the mutation was spontaneous (Hunsicker, personal communication).

Ym/+ females differ from females of the Mo-series in that their mottling is yellowish. Moreover, the vibrissae are not curly ( Hunsicker, 1968). Ym/Y is lethal. The locus is closely linked to blotchy ( Mo^blo) but how close remains to be determined (Hunsicker, personal communication).

Pewter (provisional symbol Pew), which appeared in the CBA/J strain, has only recently been described ( Fox and Eicher, 1978). Affected males are light grey and affected females are slightly mottled. Both sexes are fertile. Its relationship to Mo and Ym is currently under investigation.