关键词: 黑麂, MHC, DQA2, 多态性, 平衡选择, 跨物种进化

Abstract: A set of nested primers specific to cattle DQA loci was used to amplify genomic DNA of the black muntjac
(Muntiacus crinifrons) using PCR. The obtained sequences showed high similarity to those of DQA2 exon 2 sequences from cattle, sheep, and sika deer. Based on the sequences,a new pair of primers specific to DQA2 locus of the black muntjac was designed and used to analyze samples of this species using PCR - SSCP and sequencing. In total,four distinct DQA2 exon 2 sequences were obtained from forty individuals and no more than two sequences were detected in any of the samples at the same time. Furthermore,no insertion/ deletion or stop codon was found in the sequences. These results suggest that the four alleles obtained in this study might originate from a single DQA locus and that the locus might be expressed and functionally important. The ratio of nonsynonymy substitutes (dn)and synonymy substitutes (ds) in the peptide binding region, PBR, was significantly larger than 1 (P < 0.05), implying that the DQA2 locus might have undergone some forms of balanced selection as was supported by the results of several model tests in CODEMEL and four amino acid sites (α11、α58、α62、α66), all located in the PBR,were revealed to be acted by balancing selection. Phylogenetic relationships between DQA alleles of several artiodactyls showed that the four DQA2 alleles of black muntjac were first grouped with analogues of cattle rather than with that of sika deer,suggesting a trans-species polymorphism pattern and a common ancient DQA2 gene pedigree between black muntjac and cattle. Finally,it should be pointed out that frequencies of the four DQA2 alleles detected in this study were found to be significantly diverged and only two heterozygotes were detected from forty samples. The Whalund effect and /or null alleles existing in the process of PCR amplification may explain the allele pattern.

Key words: Black muntjac, Balancing selection, MHC, DQA2, Polymorphism, Trans-species