Pigs with the dominant white coat color phenotype carry a duplication of the KIT gene encoding the mast/stem cell growth factor receptor

Comparative mapping data suggested that the dominant white coat color in pigs may be due to a mutation in KIT which encodes the mast/stem cell growth factor receptor. We report here that dominant white pigs lack melanocytes in the skin, as would be anticipated for a KIT mutation. We found a complete association between the dominant white mutation and a duplication of the KIT gene, or part of it, in samples of unrelated pigs representing six different breeds. The duplication was revealed by single strand conformation polymorphism (SSCP) analysis and subsequent sequence analysis showing that white pigs transmitted two nonallelic KIT sequences. Quantitative Southern blot and quantitative PCR analysis, as well as fluorescence in situ hybridization (FISH) analysis, confirmed the presence of a gene duplication in white pigs. FISH analyses showed that KIT and the very closely linked gene encoding the platelet-derived growth factor receptor (PDGFRA) are both located on the short arm of Chromosome (Chr) 8 at band 8p12. The result revealed an extremely low rate of recombination in the centromeric region of this chromosome, since the closely linked (0.5 cM) serum albumin (ALB) locus has previously been in situ mapped to the long arm (8q12). Pig Chr 8 shares extensive conserved synteny with human Chr 4, but the gene order is rearranged.