Gene duplication and divergence produce divergent MHC genotypes without disassortative mating

Genes of the major histocompatibility complex (MHC) exhibit heterozygote advantage in immune defence, which in turn can select for MHC-disassortative mate choice. However, many species lack this expected pattern of MHC-disassortative mating. A possible explanation lies in evolutionary processes following gene duplication: if two duplicated MHC genes become functionally diverged from each other, offspring will inherit diverse multilocus genotypes even under random mating. We used locus-specific primers for high-throughput sequencing of two expressed MHC Class II B genes in Leach's storm-petrels, Oceanodroma leucorhoa, and found that exon 2 alleles fall into two gene-specific monophyletic clades. We tested for disassortative vs. random mating at these two functionally diverged Class II B genes, using multiple metrics and different subsets of exon 2 sequence data. With good statistical power, we consistently found random assortment of mates at MHC. Despite random mating, birds had MHC geno...主要组织相容性复合体（major histocompatibility complex, MHC）基因在免疫防御中表现出杂合子优势，这一特性反过来可能会选择出MHC异型配偶选择策略。然而，诸多物种并未呈现出预期的MHC异型交配模式。一种可能的解释源于基因复制后的进化过程：若两份复制得到的MHC基因彼此发生功能分化，即便在随机交配条件下，子代仍可继承多样的多位点基因型。我们采用位点特异性引物，对白腰叉尾海燕（Oceanodroma leucorhoa）的两个表达型MHC II类B基因进行高通量测序，发现外显子2的等位基因可划分为两个基因特异性单系群分支。我们借助多种度量指标与不同的外显子2序列数据子集，针对这两个功能分化的II类B基因开展了异型交配与随机交配的检验。凭借充足的统计效力，我们始终发现MHC位点上的配偶呈现随机配对模式。尽管存在随机交配现象，该种鸟类的MHC基因型...