Homozygosity indicators in canine MHC region of the Standard Poodle and Leonberger populations

Dog breeds are the leading examples of artificial selection, with sometimes extreme changes between the wolf-like phenotypes and current breeds. This increased selection pressure manifest in increased homozygosity throughout the genome, including the major histocompatibility complex (MHC) with large influence on the immune system. The MHC region in 98 Leonberger and 37 Standard Poodle dogs was examined using single nucleotide polymorphism (SNP) data. The overall homozygosity levels and via the runs of homozygosity (ROH) were calculated as indicators to assess the MHC regions, compared to other random parts of the dog genome. High proportion of homozygosity was observed in all examined chromosomes, ranging from 58 to 78%. The ROH was preferred to the overall level of homozygosity, as it showed the variability within the MHC regions. The homozygosity was even lower at the locations of the genes with a known effect on the immune response, confirming previous findings.