The ovine MHC class IIa is known to consist of six to eight loci located in close proximity on chromosome 20, forming haplotypes that are typically inherited without recombination. Here, we characterise the class IIa haplotypes within the Soay sheep (Ovis aries) on St. Kilda to assess the diversity present within this unmanaged island population. We used a stepwise sequence-based genotyping strategy to identify alleles at seven polymorphic MHC class IIa loci in a sample of 118 Soay sheep from four cohorts spanning 15 years of the long-term study on St. Kilda. DRB1, the most polymorphic MHC class II locus, was characterised first in all 118 sheep and identified six alleles. Using DRB1 homozygous animals, the DQA (DQA1, DQA2 and DQA2-like) and DQB (DQB1, DQB2 and DQB2-like) loci were sequenced, revealing eight haplotypes. Both DQ1/DQ2 and DQ2/DQ2-like haplotype configurations were identified and a single haplotype carrying three DQB alleles. A test sample of 94 further individuals typed at the DRB1 and DQA loci found no exceptions to the eight identified haplotypes and a haplotype homozygosity of 21.3%. We found evidence of historic positive selection at DRB1, DQA and DQB. The limited variation at MHC class IIa loci in Soay sheep enabled haplotype characterisation but showed that no single locus could capture the full extent of the expressed variation in the region.

中文翻译：

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岛屿绵羊群体中主要组织相容性复合体 IIa 类单倍型的表征。


已知绵羊 MHC IIa 类由 20 号染色体上紧邻的 6 至 8 个基因座组成，形成通常无需重组即可遗传的单倍型。在这里，我们对圣基尔达岛索伊羊 (Ovis aries) 的 IIa 类单倍型进行了表征，以评估这个无人管理的岛屿种群中存在的多样性。我们使用基于逐步序列的基因分型策略来鉴定 118 只 Soay 羊样本中 7 个多态性 MHC IIa 类基因座的等位基因，这些样本来自圣基尔达长期研究 15 年的四个队列。 DRB1 是 MHC II 类基因座中多态性最强的，它首先在所有 118 只绵羊中进行了表征，并鉴定了 6 个等位基因。使用 DRB1 纯合动物，对 DQA（DQA1、DQA2 和 DQA2 样）和 DQB（DQB1、DQB2 和 DQB2 样）基因座进行测序，揭示了八种单倍型。鉴定了 DQ1/DQ2 和 DQ2/DQ2 样单倍型配置，并且单个单倍型携带三个 DQB 等位基因。在 DRB1 和 DQA 位点分型的另外 94 个人的测试样本中发现，八个已识别的单倍型没有例外，单倍型纯合度为 21.3%。我们在 DRB1、DQA 和 DQB 上发现了历史性正选择的证据。索伊羊 MHC IIa 类基因座的有限变异使得能够进行单倍型表征，但表明没有一个基因座能够捕获该区域表达变异的全部范围。