Mottled Neuherberg (Mo(N)), a new male-lethal coat colour mutation of the house mouse (Mus musculus).

A new semidominant X-chromosomal mutation, Mottled Neuherberg (Mo(N)), which causes coat colour variegation is described. Mo(N) arose in the second postirradiation generation after 2×200 R of X-rays (24 hours apart) to oocytes of X/O mice. Heterozygous Mo(N) females have irregular patches of fully and lightly coloured fur over the whole coat with curly vibrissae. Their viability is reduced, about 3% of the heterozygotes dying prenatally and 6 to 28% dying postnatally before weaning. Survivors are fertile without externally visible abnormalities. Hemizygous Mo(N) males die in utero after implantation. The recombination frequency between Mo(N) and tabby (Ta) was 3.65±3.16% (with 95% -confidence limits). Therefore, it is suggested that Mo(N) is a new allele of the mottled (Mo) locus of the house mouse. Mo(N)-bearing ova seem to have a lower chance of becoming fertilized by wild-type spermatozoa than by Ta-bearing spermatozoa.