中文摘要：

利用牛特异性扩增DQA2第2外显子的嵌套引物,对黑麂基因组DNA进行PCR扩增和克隆测序,基于该序列设计出黑麂DQA2基因第2外显子特异性引物。利用该引物,通过PCR-SSCP以及克隆测序技术,从40个黑麂样品中获得4个不同的DQA2等位基因。没有一个个体同时具有2个以上的等位基因,所有序列均不含插入或缺失突变,不含终止密码子,因此,本研究所扩增的DQA2基因可能是表达的单基因座位。抗原结合区（Pep-tide binding region,PBR）非同义替换率（dn）显著大于同义替换率（ds）（P〈0.05）,暗示该座位曾经历过明显的正选择作用;进一步利用CODEML程序中的相关模型以及贝叶斯法检测出4个受选择作用的氨基酸位点（α11、α58、α62、α66）,这4个位点均位于PBR区。基于NJ法构建的部分偶蹄类DQA外显子2系统发生关系显示,黑麂4个DQA2等位基因与牛、羊以及梅花鹿的DQA2等位基因构成独立的进化枝,在该进化枝内,黑麂DQA2等位基因优先与牛DQA2等位基因聚类,暗示黑麂DQA2基因在进化过程中存在跨物种进化现象。上述结果表明平衡选择是维持黑麂DQA2基因多态性的主要机制。然而,本研究从40个样品中仅检测出2个杂合子,黑麂DQA2等位基因之间的频率存在显著差异,推测可能是所检测的样品来源于不同种群,由于华伦德效应（The Whalund effect）导致杂合度降低,也不排除本文所设计的引物在PCR扩增过程中存在无效等位基因。

英文摘要：

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（P0.05）,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.