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首页> 外文期刊>Journal of genetics >Maintaining evolvability
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Maintaining evolvability

机译：保持发展性

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Although molecular methods, such as QTL mapping, have revealed a number of loci with large effects, it is still likely that the bulk of quantitative variability is due to multiple factors, each with small effect. Typically, these have a large additive component. Conventional wisdom argues that selection, natural or artificial, uses up additive variance and thus depletes its supply. Over time, the variance should be reduced, and at equilibrium be near zero. This is especially expected for fitness and traits highly correlated with it. Yet, populations typically have a great deal of additive variance, and do not seem to run out of genetic variability even after many generations of directional selection. Long-term selection experiments show that populations continue to retain seemingly undiminished additive variance despite large changes in the mean value. I propose that there are several reasons for this. (i) The environment is continually changing so that what was formerly most fit no longer is. (ii) There is an input of genetic variance from mutation, and sometimes from migration. (iii) As intermediate-frequency alleles increase in frequency towards one, producing less variance (as p -> 1, p(1 - p) -> 0), others that were originally near zero become more common and increase the variance. Thus, a roughly constant variance is maintained. (iv) There is always selection for fitness and for characters closely related to it. To the extent that the trait is heritable, later generations inherit a disproportionate number of genes acting additively on the trait, thus increasing genetic variance. For these reasons a selected population retains its ability to evolve. Of course, genes with large effect are also important. Conspicuous examples are the small number of loci that changed teosinte to maize, and major phylogenetic changes in the animal kingdom. The relative importance of these along with duplications, chromosome rearrangements, horizontal transmission and polyploidy is yet to be determined. It is likely that only a case-by-case analysis will provide the answers. Despite the difficulties that complex interactions cause for evolution in Mendelian populations, such populations nevertheless evolve very well. Longlasting species must have evolved mechanisms for coping with such problems. Since such difficulties do not arise in asexual populations, a comparison of epistatic patterns in closely related sexual and asexual species might provide some important insights.
机译：尽管诸如QTL定位等分子方法已经揭示了许多影响较大的基因座，但大量的定量变异仍可能是由多种因素引起的，而每个因素影响较小。通常，它们具有较大的添加剂组分。传统观点认为，自然选择或人为选择都会消耗加性方差，从而耗尽其供给。随着时间的流逝，方差应减小，平衡时应接近零。对于健身和与之高度相关的性状，这是特别期望的。然而，种群通常具有很大的加性变异，即使经过多代定向选择，似乎也不会耗尽遗传变异。长期选择实验表明，尽管平均值发生了较大变化，但总体上继续保持了看似未减的加性方差。我建议有几个原因。 （i）环境在不断变化，因此以前最合适的环境不再存在。 （ii）突变或有时是迁移带来的遗传变异输入。 （iii）随着中频等位基因频率朝一个方向增加，产生较小的方差（如p-> 1，p（1- p）-> 0），其他原本接近零的等位基因则变得更为常见并增加方差。因此，维持了大致恒定的方差。 （iv）总是有适合度和与之密切相关的角色的选择。就该特性而言是可遗传的，后代继承了不成比例数量的基因，这些基因加性作用于该特性，从而增加了遗传变异。由于这些原因，选定的种群保留了其进化的能力。当然，作用大的基因也很重要。显着的例子是少数将teosinte变成玉米的基因座，以及动物界的主要系统发生变化。这些与复制，染色体重排，水平传播和多倍性的相对重要性尚待确定。可能只有个案分析才能提供答案。尽管存在复杂的相互作用导致孟德尔种群进化的困难，但这些种群的进化仍然很好。持久物种必须具有应对此类问题的进化机制。由于在无性种群中不会出现此类困难，因此，对密切相关的有性和无性物种的上位模式进行比较可能会提供一些重要的见解。

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