Molecular analyses of the agouti allele in the Japanese house mouse identify a novel variant of the agouti gene.

It has been thought that the Japanese house mouse carries the A allele at the agouti locus causing light-colored bellies, but they do not always show this coloration. Thus, the presence of the A allele seems to be doubtful in them. To ascertain whether the A allele is present, a two-pronged approach was used. First, we compared lengths of DNA fragments obtained from three PCRs conducted on them to the known fragment sizes generated from mouse strains exhibiting homozygosities of either a/a, A/A, or A/A. PCR I, PCR II, and PCR III amplify only in the A and A alleles, the a and A alleles, and the a allele, respectively, and we detected amplifications in strains with A/A and A/A by PCR I, in those with a/a and the Japanese house mouse by PCR II, and in those with a/a by PCR III. Second, we sequenced the exon 1A region of the agouti gene and obtained sequences corresponding to the above strains and the Japanese house mouse, but their sequences were similar to those of the a allele. We concluded that their agouti allele is not identical to the A allele and seems to be a novel type similar to the a allele.