Wall J D, Przeworski M
Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, USA.
Genetics. 2000 Aug;155(4):1865-74. doi: 10.1093/genetics/155.4.1865.
We analyze the frequency spectra of all available human nuclear sequence data sets by using a model of constant population size followed by exponential growth. Parameters of growth (more extreme than or) comparable to what has been suggested from mtDNA data can be rejected for 6 out of the 10 largest data sets. When the data are separated into African and non-African samples, a constant size no-growth model can be rejected for 4 out of 8 non-African samples. Long-term growth (i.e., starting 50-100 kya) can be rejected for 2 out of 8 African samples and 5 out of 8 non-African ones. Under more complex demographic models, including a bottleneck or population subdivision, more of the data are compatible with long-term growth. One problem with the data used here is that a subset of loci may reflect the action of natural selection as well as of demography. It remains possible that the correct demographic model is one of constant population size followed by long-term growth but that at several loci the demographic signature has been obscured by balancing or diversifying selection. However, it is not clear that the data at these loci are consistent with a simple model of balancing selection; more complicated selective alternatives cannot be tested unless they are made explicit. An alternative explanation is that population size growth is more recent (e.g., upper Paleolithic) and that some of the loci have experienced recent directional selection. Given the available data, the latter hypothesis seems more likely.
我们通过使用一个先恒定种群大小后指数增长的模型，来分析所有可用的人类核序列数据集的频谱。对于10个最大的数据集中的6个，与线粒体DNA数据所暗示的相比更为极端或相当的增长参数可被排除。当数据被分为非洲样本和非非洲样本时，对于8个非非洲样本中的4个，恒定大小无增长模型可被排除。对于8个非洲样本中的2个以及8个非非洲样本中的5个，长期增长（即始于5万至10万年前）可被排除。在更复杂的人口模型下，包括瓶颈效应或种群细分，更多的数据与长期增长相符。此处使用的数据存在的一个问题是，一部分基因座可能既反映了自然选择的作用，也反映了人口统计学特征。仍然有可能正确的人口模型是先恒定种群大小后长期增长，但在几个基因座上，人口统计学特征已被平衡选择或多样化选择所掩盖。然而，尚不清楚这些基因座的数据是否与简单的平衡选择模型一致；除非明确提出，否则更复杂的选择替代方案无法进行检验。另一种解释是种群大小增长是更近时期的（例如旧石器时代晚期），并且一些基因座经历了近期的定向选择。鉴于现有数据，后一种假设似乎更有可能。
