Li W H, Wu C I, Luo C C
J Mol Evol. 1984;21(1):58-71. doi: 10.1007/BF02100628.
We have obtained a revised estimate of the pattern of point mutation by considering more pseudogene sequences. Compared with our previous estimate, it agrees better with expectations based on the double-strand structure of DNA. The revised pattern, like the previous one, indicates that mutation occurs nonrandomly among the four nucleotides. In particular, the proportion of transitional mutations (59%) is almost twice as high as the value (33%) expected under random mutation. The same high proportion of transitions is observed in synonymous substitutions in genes. The proportion of transitional changes observed among electrophoretic variants of human hemoglobin is about the same as that predicted by the revised pattern of mutation. We also show that nonrandom mutation increases, by about 15%, the proportion of synonymous mutations due to single-nucleotide changes in the codon table, and increases, from 10% to 50%, the rate of synonymous mutation in the seven genes studied. However, nonrandom mutation reduces (by about 10%) the proportion of polar changes among nonsynonymous mutations in a gene. As far as single-nucleotide changes (in the codon table) are concerned, nonrandom mutation only slightly favors relatively conservative amino acid interchanges, and has virtually no effect on the proportions of radical changes and nonsense mutations.
通过考虑更多的假基因序列，我们获得了点突变模式的修正估计值。与我们之前的估计相比，它与基于DNA双链结构的预期结果更为吻合。与之前的模式一样，修正后的模式表明，四种核苷酸之间的突变并非随机发生。特别是，转换突变的比例（59%）几乎是随机突变预期值（33%）的两倍。在基因的同义替换中也观察到了相同的高转换比例。在人类血红蛋白的电泳变体中观察到的转换变化比例与突变修正模式预测的比例大致相同。我们还表明，非随机突变使密码子表中由于单核苷酸变化导致的同义突变比例增加了约15%，并使所研究的七个基因中的同义突变率从10%提高到了50%。然而，非随机突变降低了（约10%）基因中非同义突变中极性变化的比例。就（密码子表中的）单核苷酸变化而言，非随机突变仅略微有利于相对保守的氨基酸互换，并且对激进变化和无义突变的比例几乎没有影响。
