Palsbøll P J, Bérubé M, Jørgensen H
Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697-2525, USA.
Genetics. 1999 Jan;151(1):285-96. doi: 10.1093/genetics/151.1.285.
Between three and six tri- and tetranucleotide repeat microsatellite loci were analyzed in 3720 samples collected from four different species of baleen whales. Ten of the 18 species/locus combinations had imperfect allele arrays, i.e., some alleles differed in length by other than simple integer multiples of the basic repeat length. The estimate of the average number of alleles and heterozygosity was higher at loci with imperfect allele arrays relative to those with perfect allele arrays. Nucleotide sequences of 23 different alleles at one tetranucleotide repeat microsatellite locus in fin whales, Balaenoptera physalus, and humpback whales, Megaptera novaeangliae, revealed sequence changes including perfect repeats only, multiple repeats, and partial repeats. The relative rate of the latter two categories of mutation was estimated at 0.024 of the mutation rate involving perfect repeats only. It is hypothesized that single-strand slippage of partial repeats may provide a mechanism for counteracting the continuous expansion of microsatellite loci, which is the logical consequence of recent reports demonstrating directional mutations. Partial-repeat mutations introduce imperfections in the repeat array, which subsequently could reduce the rate of single-strand slippage. Limited computer simulations confirmed this predicted effect of partial-repeat mutations.
在从四种不同须鲸物种收集的3720个样本中，分析了三到六个三核苷酸和四核苷酸重复微卫星位点。18个物种/位点组合中有10个具有不完美的等位基因阵列，即一些等位基因的长度差异不是基本重复长度的简单整数倍。与具有完美等位基因阵列的位点相比，具有不完美等位基因阵列的位点的平均等位基因数和杂合度估计更高。对长须鲸（Balaenoptera physalus）和座头鲸（Megaptera novaeangliae）中一个四核苷酸重复微卫星位点的23个不同等位基因的核苷酸序列分析显示，序列变化包括仅完美重复、多个重复和部分重复。后两类突变的相对发生率估计为仅涉及完美重复的突变率的0.024。据推测，部分重复的单链滑动可能提供一种机制来抵消微卫星位点的持续扩展，这是最近报道的定向突变的逻辑结果。部分重复突变会在重复阵列中引入不完美，这随后可能会降低单链滑动的速率。有限的计算机模拟证实了部分重复突变的这一预测效果。
