MHC class II DRB1 and DQA2 gene polymorphisms in four indigenous breeds of sheep (Ovis aries)

Major histocompatibility complex (MHC) contains highly polymorphic genes, coding receptors that participate in the immune responses. Information of MHC polymorphism from domestic animals could be used in genetic improvement programs and could contribute to the understanding of the impact of domestication or human influence. Here, we studied the highly polymorphic genes DRB1 and DQA2 in four Mediterranean breeds of domestic sheep (Ovis aries), using SSCP method in combination with sequencing. In total 48 Ovar-DRB1 and 46 Ovar-DQA2 alleles were detected. For both genes high levels of polymorphism were recorded; DRB1 had higher functional polymorphism in the peptide binding region (PBR) whereas DQA2 had a remarkable amino acid polymorphism at full-length exon. This polymorphism detected in O. aries is consistent with heterozygote and rare allele advantage, the main mechanisms of balancing selection.