MOLECULAR-BASIS FOR THE DOMINANT WHITE PHENOTYPE IN THE DOMESTIC PIG

The change of phenotypic traits in domestic animals and crops as a res ponse to selective breeding mimics the much slower evolutionary change in natural populations. Here, we describe that the dominant white phe notype in domestic pigs is caused by two mutations in the KIT gene enc oding the mast/stem cell growth factor receptor (MGF), one gene duplic ation associated with a partially dominant phenotype and a splice muta tion in one of the copies leading to the fully dominant allele. The sp lice mutation is a G to A substitution in the first nucleotide of intr on 17 and leads to skipping of exon 17. The duplication is most likely a regulatory mutation affecting KIT expression, whereas the splice mu tation is expected to cause a receptor with impaired or absent tyrosin e kinase activity. Immunocytochemistry showed that this variant form i s expressed in 17- to 19-day-old pig embryos. Hundreds of millions of white pigs around the world are assumed to be heterozygous or homozygo us for the two mutations.