Hypervariable yellow (Ahvy), a new murine agouti mutation: Ahvy displays the largest variation in coat color phenotypes of all known agouti alleles.

A new coat color mutation, which occurred spontaneously in the C3H/HeJ strain, has been identified. The original C3H/HeJ male mouse carrying the mutation was unusual because its coat color appeared mostly yellow, in contrast to the wild-type agouti coat normally exhibited by mice of the C3H/HeJ strain. Genetic crosses showed that the mutant phenotype was inherited as a single autosomal dominant gene. The mutation was backcrossed onto a C57BL/6J background and tested for allelism with the agouti locus. The results showed that the mutation, named hypervariable yellow (Ahvy), is a new allele of the agouti locus. Ahvy is unique because mice carrying the mutation can display a range of coat color from pure yellow to almost pure black. The Ahvy mutation is responsible for the largest range of coat color phenotypes yet identified for any single agouti mutation.