Abstract: Sequence variation at the second exon of the MHC-DQB locus was investigated on 25 spotted seals (Phoca largha)in Liaodong Bay,China. Of the 141 nucleotides scored,21 variable sites were detected,defining 12 haplotypes, differing by 25.5% at the amino acid level. The nucleotide diversity was from 0.0071 to 0.1064 (average 0.0577),and the base difference was from 1bp to 15 bp (average 8bp). These results showed relatively high genetic diversity in this population compared to other pinniped species.  The high rate of non-synonymous versus synonymous substitution especially in the peptide-binding region (PBR)suggested strong balancing selection for maintaining high MHC diversity at the MHCDQB locus. Eleven individuals holding more than two alleles per individual indicated the duplication of DQB gene.

Key words: Conservation, DQB, Genetic diversity, Major histocompatibility complex (MHC), Spotted seal (Phoca largha)

摘要： 本文从25 份斑海豹样本中获得141 bp 片段,发现21 个变异位点,定义了12 个MHC-DQB 等位基因,氨基酸变异率为25.5% 。等位基因之间的遗传距离范围是0. 0071 ～ 0.1064,平均值为0.0577,不同等位基因之间的碱基差异是1 ～ 15 bp,平均差异数为8 bp。与其他鳍足类动物对比后发现,斑海豹MHC-DQB 表现出较丰富的多态性。非同义替换率明显高于同义替换率,由此造成的氨基酸替换集中在肽结合位点PBR 附近,表明DQB 基因受到强烈的平衡选择作用。11 个样本出现多于两条等位基因的情况,推测存在基因重复现象。

关键词: 斑海豹, 主要组织相容性复合体(MHC), DQB, 遗传多样性, 保护