Paterson S
Department of Genetics, University of Cambridge, England.
J Hered. 1998 Jul-Aug;89(4):289-94. doi: 10.1093/jhered/89.4.289.
Evidence for selective maintenance of genetic diversity at the major histocompatibility complex (MHC) was investigated in an unmanaged population of Soay sheep on the island of Hirta, St. Kilda, Scotland. Animals were sampled as newborn lambs and between 887 and 1209 individuals were typed at each of five microsatellite markers located either within or flanking the ovine MHC. Markers located within the MHC showed high levels of linkage disequilibrium with each other but not with flanking markers. Hardy-Weinberg proportions were found for all loci; however, two of the three markers within the MHC showed relatively even allele frequency distributions that were unlikely to have resulted from neutrality and suggest the action of recent balancing selection. Sequence polymorphism was examined within DRB, a class II gene immediately adjacent to one of the microsatellite markers, and high correlation of sequence polymorphism with microsatellite length variation was found. An excess of nonsynonymous substitution compared to synonymous substitution was found, indicating the action of balancing selection favoring novel MHC variants and hence increased diversity over a longer time period.
在苏格兰圣基尔达岛希尔塔岛上的一个未管理的索艾羊种群中，研究了主要组织相容性复合体（MHC）处遗传多样性的选择性维持证据。动物在新生羔羊时进行采样，在位于绵羊MHC内部或侧翼的五个微卫星标记中的每一个标记处，对887至1209只个体进行了基因分型。位于MHC内的标记彼此之间显示出高度的连锁不平衡，但与侧翼标记没有连锁不平衡。所有位点均符合哈迪-温伯格比例；然而，MHC内的三个标记中的两个显示出相对均匀的等位基因频率分布，这不太可能是由中性导致的，表明近期存在平衡选择作用。在与其中一个微卫星标记紧邻的II类基因DRB内检查了序列多态性，发现序列多态性与微卫星长度变异高度相关。与同义替换相比，发现非同义替换过多，表明平衡选择有利于新的MHC变体，从而在更长的时间段内增加了多样性。
