Orr H Allen
Department of Biology, University of Rochester, Rochester, New York, 14627.
Evolution. 1998 Aug;52(4):935-949. doi: 10.1111/j.1558-5646.1998.tb01823.x.
We know very little about the genetic basis of adaptation. Indeed, we can make no theoretical predictions, however heuristic, about the distribution of phenotypic effects among factors fixed during adaptation nor about the expected "size" of the largest factor fixed. Study of this problem requires taking into account that populations gradually approach a phenotypic optimum during adaptation via the stepwise substitution of favorable mutations. Using Fisher's geometric model of adaptation, I analyze this approach to the optimum, and derive an approximate solution to the size distribution of factors fixed during adaptation. I further generalize these results to allow the input of any distribution of mutational effects. The distribution of factors fixed during adaptation assumes a pleasingly simple, exponential form. This result is remarkably insensitive to changes in the fitness function and in the distribution of mutational effects. An exponential trend among factors fixed appears to be a general property of adaptation toward a fixed optimum.
我们对适应的遗传基础知之甚少。实际上，无论多么具有启发性，我们都无法对适应过程中固定的因素之间的表型效应分布，或对固定的最大因素的预期“大小”做出理论预测。对这个问题的研究需要考虑到，在适应过程中，种群通过有利突变的逐步替代逐渐接近表型最优值。利用费希尔的适应几何模型，我分析了这种趋近最优值的方法，并推导出适应过程中固定因素大小分布的近似解。我进一步推广这些结果，以允许输入任何突变效应分布。适应过程中固定因素的分布呈现出一种令人愉悦的简单指数形式。这一结果对适应度函数和突变效应分布的变化非常不敏感。固定因素之间的指数趋势似乎是朝着固定最优值适应的一个普遍特性。
