Abstract: 【Objective】 The Tibetan sheep DQA1 gene polymorphism, determine its allele number, nucleotide polymorphism sites, amino acid polymorphism sites, the genetic relationship and evolutionary significance of the alleles were studied. 【Method】Variation of DQA1 gene in the 900 Tibetan sheep was investigated by amplification of exon 2 using PCR, followed by single-strand conformational polymorphism (SSCP) analysis, cloning, DNA sequencing and sequence data analysis. 【Result】Seventeen alleles were identified including a null allele at the DQA1 locus. Another five alleles were found in the DQA1 gene in this study. Fifty-six nucleotide polymorphism sites and 27 amino acid polymorphism sites were identified in 16 sheep DQA1 gene haplotypes. 【Conclusion】The study indicated that a high level of sequence polymorphism existed in Tibetan sheep DQA1 gene, the population may have more genetic resources. Tibetan sheep DQA1 gene may be differentiated into two major categories alleles from two mutant alleles at first. DQA1 gene in Tibetan sheep and cattle has high homology, which indicated that DQA1 gene in sheep and cattle may come from primordial sequences that were present in a common ancestor and have persisted in the sheep and cattle populations since their divergence, and the observation showed that sheep and cattle share similar allelic sequences may be evidence of the need for a specific immune response to a common pathogen. A new nucleotide mutation (A/G) was discovered in 139 site of new alleles C, and it is the synonymous mutation. Five new alleles have near genetic relationship, they maybe came from the same allele by mutantion.

Key words: DQA1 gene, polymorphism, polymerase chain reaction-single strand conformational polymorphism, Tibetan Sheep