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There are many coat colors in the laboratory mouse, Mus musculus. On the basis of traditional genetics, there are four loci, A-D, related to coat color expressions. As shown by previous studies, Japanese wild mice have gray backs and white bellies and are assumed to carry the A(w) allele at the A (agouti) locus, which is dominant over any other alleles. However, we collected Japanese wild mice from central Honshu with black coats. To understand this black coat expression, we performed cross experiments concerning the four loci using wild-caught mice and DBA/2 laboratory mice from the standpoint of traditional genetics. The offspring of the current crosses showed the wild type, the blackish type, and the intermediate type from some combinations of parents. Considering the coat colors of the offspring, we did not obtain any evidence that the Japanese wild mice always carry the A(w) allele at the A locus. Furthermore, we were not able to explain the current coat color expressions using the traditional logic with regard to the A-D loci and concluded that it is possible for another locus (loci) to be related to the coat color expressions. On the other hand, skull characteristics and external body measurements of the captured wild mice were fundamentally different from those of DBA/2 and offspring from captured wild mice and DBA/2 combinations. Thus, we concluded that the Japanese wild mice had original criteria from a morphological viewpoint.

We examined pelage color variation in wild populations of black rats (the Rattus rattus species complex) in the Yambaru forest area, northern Okinawa Island, Ryukyu Archipelago, Japan. Our field study revealed that 8.7% (38/438) and 0.2% (4/2500) of rats exhibited two types of coat color: white spotting and melanism, respectively. Using 34 representative animals, the phylogeography of the population was inferred using a nuclear gene marker, i.e., sequences (954 bp) of the melanocortin-1 receptor (Mc1r) gene responsible for the melanistic form in black rats. Four sequences from Okinawa were characterized as R. tanezumi, the Asian strain of black rat. Notably, neither of the phenotypic characters of white spotting or melanism was associated with the Mc1r haplotypes. Analysis of mitochondrial cytochrome b (Cytb) sequences (1140 bp) revealed that four haplotypes recovered from Okinawa clustered with the clade of R. tanezumi and differed by one or more bases from haplotypes at other localities in Japan and Asian countries. Thus, both variants may have arisen in the native rat population of Okinawa without interaction with the lineage of R. rattus, which exhibits a worldwide distribution and displays such coat color variants. The Yambaru population of black rats has thus experienced its own evolutionary history in allopatry for a substantial period of time (e.g., 10,000 years), which has preserved valuable genetic polymorphisms and will be useful for assessing the ecological consequences of genetic variation in natural populations.

In order to develop a genotyping method that can be used in the registration procedure for Thoroughbreds, we developed a method for simultaneously genotyping multiple coat colour genes on the basis of single nucleotide polymorphism typing by using the SNaPshot(TM) technique. This method enabled precise and reasonable detection of causal mutations; it was effective for genotyping of MC1R, ASIP, and SLC45A2 at the Extension (E), Agouti (A), Cream dilution (C) loci, and the possibility of identification of rare variants of MC1R, EDNRB and KIT at the E, Overo (O) and Sabino 1 (SB1) loci, respectively, was also indicated. It was considered that this genotyping method would provide information not only for the registration of Thoroughbreds but also for the preservation of phenotypic characters, such as coat colour, of endangered Misaki native horses in Japan. Therefore, genetic variations at the five coat colour loci were investigated in 1111 Thoroughbred and 99 Misaki native horses. Allele frequencies at the polymorphic E and A loci were estimated, and the proportions of basic coat colours that could be expected in the Thoroughbred population were bay, 0.662; black, 0.070; chestnut, 0.268. In the Misaki population, they were bay, 0.792; black, 0.129; chestnut, 0.080. The data presented were the first of its kind on genetic coat colour variation, and will be important with regard to the registration of Thoroughbreds and the management of Misaki horses.

A new inbred strain JF1 (Japanese Fancy Mouse 1) was established from a strain of fancy mouse. Morphological and genetical analysis indicated that the mouse originated from the Japanese wild mouse, Mus musculus molossinus. JF1 has characteristic coat color, black spots on the white coat, with black eyes. The mutation appeared to be linked to an old mutation piebald (s). Characterization of the causative gene for piebald, endothelin receptor type B (ednrb), demonstrated that the allele in JF1 is same as that of classic piebald allele, suggesting an identical origin of these two mutants. Possibly, classic piebald mutation was introduced from the Japanese tame mouse, which was already reported at the end of the 1700s. We showed that JF1 is a useful strain for mapping of mutant genes on laboratory strains owing to a high level of polymorphisms in microsatellite markers between JF1 and laboratory strains. The clarified genotypes of JF1 for coat color are "aa BB CC DD ss".