Abstract：Major histocompatibility complex (MHC), one of the vital functional gene families in vertebrates, encodes MHC molecule which has the function and ability to maintain the organism adapt to environmental changes from generation to generation, and is the best genetic marker for investigating adaptive evolution in animals. Tibetan sheep (Ovis aries), the main livestock resources in Qinghai-Tibetan plateau, was chosen as research object, and the genetic characteristics of DQA genes in 5 ecological Tibetan sheep populations from Gansu (Oula, Qiaoke and Ganjia type) and Qinghai (Oula and plateau type) were investigated using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) techniques in this study, which aimed to reveal its adaptive evolutionary mechanism in plateau Tibetan sheep. The results showed that 33 alleles and 125 SNPs were discovered in 2 genes of Tibetan sheep DQA locus. This indicated that the DQA genes in 5 ecological Tibetan sheep populations exhibited abundant polymorphism. Subsequent analysis demonstrated that balancing selection was one of the mechanisms to maintain the polymorphism of DQA genes in Tibetan sheep. The changes of DQA genes among groups in 5 ecological Tibetan sheep from Gansu and Qinghai were less than those among population with groups, suggesting that the DQA genes in Tibetan sheep generates positive selection and adaptive evolution. This research results will provide basic data for genetic improvement and germplasm innovation of Tibetan sheep.
