ABSTRACT
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.
Subject(s)
Chromosome Mapping , Chromosomes, Human, Pair 4 , Hair Color/genetics , Proto-Oncogene Proteins c-kit/genetics , Swine/genetics , Animals , Base Sequence , DNA Primers , Exons , Genes, Dominant , Genetic Linkage , Genetic Markers , Humans , In Situ Hybridization, Fluorescence , Molecular Sequence Data , Phenotype , Polymerase Chain Reaction , Polymorphism, Single-Stranded Conformational , Recombination, Genetic , Sequence Homology, Nucleic AcidABSTRACT
A comprehensive linkage map, including 236 linked markers with a total sex-average map length of about 2300 cM, covering nearly all parts of the pig genome has been established. Linkage groups were assigned to approximately all 18 autosomes, the X chromosome and the X/Y pseudoautosomal region. Several new gene assignments were made including the assignment of linkage group U1 (EAK-HPX) to chromosome 9. The linkage map includes 77 types I loci informative for comparative mapping and 72 in situ mapped markers physically anchoring the linkage groups on chromosomes. A highly significant heterogeneity in recombination rates between sexes was observed with a general tendency towards an excess of female recombination. The average ratio of female to male recombination was estimated at 1.4:1 but this parameter varied between chromosomes as well as between regions within chromosomes. An intriguing finding was that blood group loci were overrepresented at the distal ends of linkage groups.
