Genetic characterization of belly spot and splashed white coat color in horses

Abstract: Coat color studies are important because in some breeds only certain colors are permitted; another reason is that some coat colors are associated with diseases. The purpose of this master thesis is to shed some light on the inheritance pattern of the splashed white coat color and belly spot in horses. There is so far no indication that splashed white or belly spot would be associated with a disorder. The Swedish Warmblood (SWB) was chosen for the belly spot phenotype and the Icelandic horse was chosen because they show the splashed white phenotype. One hypothesis is that there is a similar genetic background to these phenotypes.For the study half sib families to six SWB stallions and one Icelandic horse stallion have been used. The samples for the study were collected from the Animal Genetics Laboratory at the Swedish University of Agricultural Science. The material includes 356 horses in total; they have been genotyped for 8 markers close to three candidate genes. Genotypes were determined by PCR amplification of markers and capillary electrophoresis. Pedigree information and phenotypic information have been used to perform an association study and linkage analysis on the results. The phenotypic and pedigree information was retrieved from the SWB Association (ASVH). The inheritance study of the half-sib families included all offspring and mares to each of the SWB stallions. Splashed white, belly spot and white leg markings show a complex inheritance pattern. The Kitligand gene is most likely involved in the splashed white and belly spot phenotypes while the Kit gene is likely to be involved in the white leg markings. White facial markings are most likely controlled by one major gene Kit, blaze seem to be a dominant trait whereas white lower lip seem to be recessive. The extension of white markings is affected by the coat color; chestnuts have more extensive white pattern while black and bay horses have more restricted areas of white.