Biodesign Center for Mechanisms of Evolution, Arizona State University, Tempe, AZ 85287, USA.
Knowledge Enterprise, Arizona State University, Tempe, AZ 85287, USA.
Genetics. 2023 Jul 6;224(3). doi: 10.1093/genetics/iyad091.
Numerous organismal traits, particularly at the cellular level, are likely to be under persistent directional selection across phylogenetic lineages. Unless all mutations affecting such traits have large enough effects to be efficiently selected in all species, gradients in mean phenotypes are expected to arise as a consequence of differences in the power of random genetic drift, which varies by approximately five orders of magnitude across the Tree of Life. Prior theoretical work examining the conditions under which such gradients can arise focused on the simple situation in which all genomic sites affecting the trait have identical and constant mutational effects. Here, we extend this theory to incorporate the more biologically realistic situation in which mutational effects on a trait differ among nucleotide sites. Pursuit of such modifications leads to the development of semi-analytic expressions for the ways in which selective interference arises via linkage effects in single-effects models, which then extend to more complex scenarios. The theory developed clarifies the conditions under which mutations of different selective effects mutually interfere with each others' fixation and shows how variance in effects among sites can substantially modify and extend the expected scaling relationships between mean phenotypes and effective population sizes.
许多生物特征，尤其是在细胞水平上，很可能在系统发育谱系中受到持续的定向选择。除非所有影响这些特征的突变都具有足够大的影响，以便在所有物种中得到有效选择，否则由于随机遗传漂变的能力差异，平均表型的梯度将作为一个结果出现，而随机遗传漂变的能力差异在大约五个数量级上在生命之树上变化。之前的理论研究着眼于在何种条件下可以产生这种梯度，重点研究了影响特征的所有基因组位点具有相同且恒定的突变效应的简单情况。在这里，我们将这一理论扩展到更符合生物学实际的情况，即一个特征的突变效应在核苷酸位点之间存在差异。对这种修饰的追求导致了单效模型中通过连锁效应产生选择干扰的方式的半分析表达的发展，然后扩展到更复杂的情况。所发展的理论阐明了不同选择效应的突变相互干扰固定的条件，并展示了位点之间效应的差异如何能够显著改变和扩展平均表型与有效种群大小之间的预期比例关系。
