Detection of a quantitative trait locus for ham weight with polar overdominance near the ortholog of the callipyge locus in an experimental pig F2 population

The distal part of SSC7, which contains the ortholog to the ovine region encompassing the callipyge locus, was analyzed in a Pietrain F-2 resource population comprising more than 2,700 offspring. The aim of the study was to map QTL affecting carcass traits comparable with the callipyge phenotype in sheep. We applied an interval mapping approach using 14 microsatellite markers and detected 3 QTL with small effects. The first QTL affects fat thickness on the middle of the back, with no detectable impact on fat sizes at other places on the back, whereas the second QTL affects side fat thickness. The third QTL influences the ham weight and shows a clear parent-of-origin-dependent effect in the form of maternal polar overdominance. It is not located at the position of the imprinting cluster including the callipyge locus, but 7 cM proximal.