Quantitative trait loci that modify the sootiness of yellow pigmentation in KK-A y /a mice

Compared with C57BL/6J-A y /a, KK-A y /a mice have yellow fur that is markedly darker. Furthermore, there is a considerable variation in the tone of color with a continuous range in F2 progeny produced from C57BL/6J females and KK-A y /a males. The aims of this study are to reveal the phenotypic differences between the two A y congenic strains and to elucidate the genetic factors responsible for the sooty yellow pigmentation in the KK background. On the basis of a chemical analysis, the sootiness in KK-A y /a was the result of increased eumelanin (PTCA) and decreased pheomelanin (AHP). A statistically significant QTL was identified on Chromosome (Chr) 15, responsible for the AHP content. No significant loci responsible for PTCA were identified. On the other hand, on the basis of an optical analysis for color difference and overall sootiness, significant evidence of linkage was identified on the proximal part of Chr 15, in the region similar to AHP QTL. The overall sootiness is thus controlled solely by the locus on Chr 15 in F2 progeny; however, the KK allele at this locus significantly increased the AHP content.