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 marke dly darker. Furthermore, there is a considerable variation in the tone of c olor with a continuous range in F-2 progeny produced from C57BL/6J females and KK-A(y)/a males. The aims of this study are to reveal the phenotypic di fferences between the two A(y) congenic strains and to elucidate the geneti c factors responsible for the sooty yellow pigmentation in the KK backgroun d. 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 sta tistically significant QTL was identified on Chromosome (Chr) 15, responsib le for the AHP content. No significant loci responsible for PTCA were ident ified. On the other hand, on the basis of an optical analysis for color dif ference and overall sootiness, significant evidence of linkage was identifi ed on the proximal part of Chr 15, in the region similar to AHP QTL. The ov erall sootiness is thus controlled solely by the locus on Chr 15 in F-2 pro geny; however, the KK allele at this locus significantly increased the AHP content.