Environmental stress and mutational load in diploid strains of the yeast Saccharomyces cerevisiae
Environmental stress and mutational load in diploid strains of the yeast Saccharomyces cerevisiae
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DOI：
10.1073/pnas.021390798
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发表时间：
2001-01-30
影响因子：
11.1
通讯作者：
Korona, R
中科院分区：
文献类型：
--
作者：
Szafraniec, K;Borts, RH;Korona, R
如果从人类或许多野生和驯化物种相对良好的健康状况来判断，自发突变对种群造成的永久性污染的负面影响似乎并不大。在二倍体中，新的突变通常位于杂合位点，因此被野生型等位基因所掩盖，这在一定程度上解释了这一事实。表型水平上的突变表达也可能强烈依赖于环境因素，例如，有害等位基因在有利条件下更容易得到补偿。目前的实验使用二倍体酵母菌株，其中由于缺少错配修复蛋白，突变率很高。这种突变在杂合位点上产生了许多新的等位基因。当环境是良性时，它们对健康没有明显的影响。当应用热冲击时，可以看到非常不同的结果，其中突变污染的克隆的适应性比未突变的克隆更低，更多样化。这表明，自发突变所带来的遗传负荷在有利条件下可以被低估甚至忽略。因此，当环境条件越来越差时，遗传变异可能会更高，自然选择也会更激烈。这些结论至少适用于直接源于自发突变的变异成分（而不是由历史选择产生的变异）。
The negative effect of permanent contamination of populations because of spontaneous mutations does not appear to be very high if judged from the relatively good health of humans or many wild and domesticated species. This is partly explained by the fact that, in diploids, the new mutations are usually located in heterozygous loci and therefore are masked by wild-type alleles. The expression of mutations at the phenotypic level may also strongly depend on environmental factors if, for example, deleterious alleles are more easily compensated under favorable conditions. The present experiment uses diploid strains of yeast in which mutations arise at high rates because a mismatch-repair protein is missing. This mutagenesis resulted in a number of new alleles that were in heterozygous loci. They had no detectable effect on fitness when the environment was benign. A Very different outcome was seen when thermal shock was applied, where fitness of the mutation-contaminated clones was lower and more diverse than that of the nonmutagenized crones. This shows that the genetic load conferred by spontaneous mutations can be underestimated or even overlooked in favorable conditions. Therefore, genetic variation can be higher and natural selection more intense when environmental conditions are getting poorer. These conclusions apply, at least, to that component of Variation that directly originates from spontaneous mutations (as opposed to the variation resulting from the history of selection).