Abstract: In present study,the genetic variances of SLA DRB exon 2 of Chinese wild boar (Sus scrofa) were analyzed, and the effects of selection at the locus in different geographic environments were addressed as well. The sequence analysis showed that the rates of nonsynonymous substitutions per nonsynonymous site was 2.95 times higher than the rates of synonymous substitutions per synonymous sites at the antigen binding sites. The results indicated that balancing selection may have acted on the antigen binding sites in the evolution of Chinese wild boars. The phylogeny analysis based on nucleotide variation revealed that 15 alleles form Chinese wild boars formed one cluster,and there was no trans-species polymorphism. However,the high similarity of amino acids sequence of SLA-DRB* nnu6 and human DRB exon 2 may indicate convergent evolution under same natural selection pressure. The results showed that genetic diversity of SLA DRB exon 2 in S. s. ussuricus was significantly lower than S s moupinensis and S. s.chirodonta, which may indicated a consistent relation ship between SLA diversity and parasite or other factors in different climatic and geographical environment.

Key words: Balancing selection, DRB exon 2, Genetic variation, Phylogeny, Sus scrofa

摘要： 本文基于135 头野猪样本中检测到的15 种SLA DRB 基因exon 2 序列的遗传变异分析,探讨DRB 基因在不同地理区域中自然选择的变化特征。研究发现DRB 基因exon 2 抗原结合位点的非同义替换率为同义替换率的2. 95 倍,表明该位点受到平衡选择的强烈作用。在系统发生分析中,在基于核苷酸序列构建的NJ 树中, 野猪DRB 位点的15 种等位基因全部聚为一枝,没有发现跨种多态现象;而在基于氨基酸序列构建的系统发生树中,野猪SLA - DRB nnu6 和人DRB 基因exon 2 片段聚在一起,这种氨基酸残基的高度相似可能是由于自然选择压力下产生的趋同。野猪DRB 基因exon 2 的序列多态性分析表明,东北野猪基因多态性低于四川野猪和华南野猪,这可能与不同气候条件和地理环境下的寄生虫等因素对SLA 等位基因变异的影响存在差异有关。

关键词: 野猪, DRB exon 2, 遗传变异, 平衡选择, 系统发生