F₁-A^y mice between RR (aabbCC) and C57BL/6J-A^y (A^yaBBCC) have a much darker yellow coat color than do C57BL/6J-A^y. Quantitative trait locus (QTL) analysis was carried out to identify genes responsible for the darker modification of the yellow coat color (this has been traditionally termed "sable"). A significant sable QTL was identified on chromosome 1 (Dmyaq4, LOD score 15.5 for lightness, and 13.4 for color difference), in a chromosomal position similar to that of Dmyaq2, a sable QTL previously identified in C3H/HeJ. Another significant sable QTL was identified on chromosome 4 (Dmyaq5, LOD score 5.6 for lightness, and 4.3 for color difference) near the tyrosinase-related protein 1 (Tyrp1) locus. The effect of Dmyaq5 was significant only in the presence of the RR allele at Dmyaq4, suggesting that the Dmyaq4 (as well as Dmyaq2) is a novel coat color gene that may act up-stream of Tyrp1 signaling to increase eumelanin production.


(Edited by Masanori OTSUKA, M.J.A.)