Shimmin L C, Chang B H, Hewett-Emmett D, Li W H
Center for Demographic and Population Genetics, University of Texas, Houston 77225.
J Mol Evol. 1993 Aug;37(2):160-6. doi: 10.1007/BF02407351.
It is commonly believed that the rate of mutation is much higher in males than in females because the number of germ-cell divisions per generation is much larger in males than in females. However, the precise magnitude of the male-to-female mutation rate ratio (alpha m) remains unknown. Recently there have been efforts to estimate alpha m by using DNA sequence data from different species. We have studied the potential problems in such an approach. We found that the rate of synonymous substitution varies about fivefold among X-linked genes, as large as the variation among autosomal genes. This large variation makes the assumption of selective neutrality of synonymous changes dubious, so one should be cautious in using the synonymous rates in X-linked and autosomal genes to estimate alpha m. A similar difficulty was also observed in using nonhomologous intron sequences to estimate alpha m. Contrary to the expectation that X-linked sequences should evolve more slowly than autosomal sequences, the Alu repeat in the last intron of the X-linked zinc finger gene has evolved faster than the four autosomal Alu repeats used in this study. It appears that the best way to estimate alpha m is to use homologous sequences. However, such sequences may be involved in gene conversion events. In fact, we found evidence that the Y-linked and X-linked zinc finger genes have been involved in multiple conversion events during primate evolution. Thus, the possibility of gene conversion should be considered when using homologous sequences to estimate alpha m.
人们普遍认为，男性的突变率比女性高得多，因为男性每代生殖细胞的分裂次数比女性多得多。然而，男性与女性突变率之比（αm）的确切数值仍然未知。最近，人们一直在努力通过使用来自不同物种的DNA序列数据来估计αm。我们研究了这种方法中存在的潜在问题。我们发现，X连锁基因之间的同义替换率变化约为五倍，与常染色体基因之间的变化一样大。这种巨大的变化使得同义变化具有选择性中性的假设值得怀疑，因此在使用X连锁基因和常染色体基因中的同义率来估计αm时应谨慎。在使用非同源内含子序列估计αm时也观察到了类似的困难。与X连锁序列应该比常染色体序列进化得更慢的预期相反，X连锁锌指基因最后一个内含子中的Alu重复序列比本研究中使用的四个常染色体Alu重复序列进化得更快。看来估计αm的最佳方法是使用同源序列。然而，这些序列可能参与了基因转换事件。事实上，我们发现有证据表明，在灵长类动物进化过程中，Y连锁和X连锁锌指基因参与了多次转换事件。因此，在使用同源序列估计αm时应考虑基因转换的可能性。
