Coat Color Inheritance of the Roof Rat in Hawaii

This paper reviews color polymorphism and nomenclature of roof rats of European ancestral stock in Hawaii. These rats are generally referable to Rattus rattus rattus (L.) and exhibit three pelage phenotypes controlled by a series of alleles at each of two gene loci. The standard wild-type rat has an agouti dorsum and white venter; one mutant has a gray venter in place of the white. There are two phenotypically indistinguishable mutant black forms, as was first disclosed in 1865 and explained genetically in 1926. One black results from a recessive gene pair (aa) at one locus, and the other is from a dominant gene (E′) at a second locus. Breeding tests with roof rats from Hawaii affirm that the geneticists' findings apply without deviation to this population. Agouti series alleles Aw+Aw+, AdAd, aa, and the black extension series, E+E+, E′ E′, were found in random combination among more than 100 rats tested. Apparent intergrades between standard-type rats and gray-bellied mutants resulted from soiling of the pelage, but all such rats could be accurately classed to phenotype.