Webster Matthew T
Department of Medical Biochemistry and Microbiology, Uppsala University, Box 582, 75123 Uppsala, Sweden.
Gene. 2009 Aug 15;443(1-2):70-5. doi: 10.1016/j.gene.2009.05.006. Epub 2009 May 20.
There is a large variation in divergence times across genomic regions between human and chimpanzee. It has been suggested that this could partly result from selection against ancestral gene flow between incipient species in regions of the genome containing genetic incompatibilities. It is possible that such barriers to gene flow could arise in specific genes or in chromosomal inversions. I analysed patterns of lineage sorting that occur between human, chimpanzee and gorilla genomic sequences by examining divergent site patterns in >18 Mb genomic alignments. I develop a method to normalise site patterns by the mutational spectrum to minimise errors caused by misinference caused by recurrent mutation. Here I show that divergence times appear to be uniform between coding and noncoding sequences and between inverted and non-rearranged portions of chromosomes. I therefore find no evidence to support the large-scale accumulation of genetic incompatibilities at speciation genes or chromosomal inversions in the ancestral population of humans and chimpanzees. In addition, site patterns that are discordant with the species tree occur more frequently in regions with high human recombination rates. This could indicate the action of selective sweeps in the ancestral population, but could also be indicative of increased rates of homoplasy in these regions. I argue that these observations are compatible with a neutral allopatric model of speciation.
人类和黑猩猩基因组区域的分化时间存在很大差异。有人认为,这可能部分是由于在包含遗传不相容性的基因组区域中,对初始物种之间祖先基因流的选择作用。基因流的这种障碍可能出现在特定基因或染色体倒位中。我通过检查超过18 Mb基因组比对中的分歧位点模式,分析了人类、黑猩猩和大猩猩基因组序列之间发生的谱系分选模式。我开发了一种方法,通过突变谱对位点模式进行归一化,以尽量减少由反复突变导致的错误推断所引起的误差。在这里,我表明编码序列和非编码序列之间以及染色体的倒位部分和非重排部分之间的分化时间似乎是一致的。因此,我没有发现证据支持在人类和黑猩猩的祖先种群中,物种形成基因或染色体倒位处存在大规模的遗传不相容性积累。此外,与物种树不一致的位点模式在人类重组率高的区域更频繁出现。这可能表明在祖先种群中存在选择性清除的作用,但也可能表明这些区域中同塑性增加的速率。我认为这些观察结果与物种形成的中性异域模型是相符的。