Hedrick P W, Lee R N, Parker K M
Department of Biology, Arizona State University, Tempe, AZ 95287, U.S.A.
Heredity (Edinb). 2000 Dec;85(Pt 6):617-24. doi: 10.1046/j.1365-2540.2000.00805.x.
We have examined in Mexican wolves and related canids the amount of genetic variation for a class II gene in the major histocompatibility complex (MHC), thought to be part of the most important genetic basis for pathogen resistance in vertebrates. In Mexican wolves, descended from only seven founders over three lineages, there were five different alleles. These were in three phylogenetic groups, only one of which was shared between lineages. Using single stand conformation polymorphism (SSCP), we found that in samples of animals from the two polymorphic lineages, the observed heterozygosity was 0.74 and the genotypes were not different statistically from Hardy-Weinberg proportions. The Ghost Ranch lineage of Mexican wolves was monomorphic for the locus, consistent with the lower level of variation found previously for microsatellite loci and predicted from pedigree analysis. Samples of grey wolves, red wolves, and coyotes had 16 additional alleles. One Mexican wolf allele was also found in grey wolves and another allele was shared between grey and red wolves. Most of the nucleotide variation resulted in amino acid variation and there were five different amino acids found at two different positions. Only two of the 21 variable amino acid positions had solely synonymous nucleotide variation. The average heterozygosity for eight individual amino acid positions in the Mexican wolves was greater than 0.4. The estimated rate of nonsynonymous substitution was 2.5 times higher than that for synonymous substitution for the putative antigen binding site positions, indicative of positive selection acting on these positions. Examination of the known dog sequences for this locus showed that one of the Mexican wolf alleles was found in dogs and that the allele found in both grey and red wolves is also found in dogs.
我们研究了墨西哥狼及相关犬科动物主要组织相容性复合体（MHC）中II类基因的遗传变异量，该基因被认为是脊椎动物病原体抗性最重要的遗传基础的一部分。墨西哥狼仅由三个谱系中的七个奠基者繁衍而来，有五个不同的等位基因。这些等位基因分属三个系统发育组，其中只有一个在谱系间共享。使用单链构象多态性（SSCP）方法，我们发现来自两个多态性谱系的动物样本中，观察到的杂合度为0.74，基因型在统计学上与哈迪-温伯格比例无差异。墨西哥狼的幽灵牧场谱系在该位点是单态的，这与之前在微卫星位点发现的较低变异水平一致，并且从系谱分析中也可预测到。灰狼、红狼和郊狼的样本还有另外16个等位基因。在灰狼中也发现了一个墨西哥狼等位基因，另一个等位基因在灰狼和红狼之间共享。大多数核苷酸变异导致了氨基酸变异，在两个不同位置发现了五种不同的氨基酸。21个可变氨基酸位置中只有两个仅有同义核苷酸变异。墨西哥狼中八个单独氨基酸位置的平均杂合度大于0.4。对于假定的抗原结合位点位置，非同义替换的估计速率比同义替换高2.5倍，这表明这些位置受到正选择作用。对该位点已知的犬类序列进行检查发现，在犬类中发现了一个墨西哥狼等位基因，并且在灰狼和红狼中都发现的等位基因在犬类中也存在。
