生物谷报道：牛津大学的科学家近日在《美国人类遗传学杂志》发表研究论文，利用贝叶斯算法估算线粒体替代率，结果支持“人类走出非洲”的时间和线粒体水平上的“人类共同祖先”的生存年代，该时间晚于先前估计的时间。
准确地估计线粒体替代率是人类分子进化研究的核心内容。但因为先前的研究采用了大量不同的方法和数据组合，使得比较研究存在一定困难。
故此，牛津大学的科学家根据177个人类线粒体基因组的一组数据，使用松散分子钟的贝叶斯系统进化分析方法，估计了不同数据组合的替代率。科学家比较了多重内校准（生物地理）和传统的外校准（人猿分化）的结果。研究结果表明，使用不同的数据组合和较准方法计算得到的替代率和分化时间相差很大。总体上，研究支持“人类走出非洲”的时间和线粒体水平上的“人类共同祖先”的生存年代，该时间晚于先前估计的时间。这项研究与考古学和解剖学水平的研究结果一致，也得到源于核DNA和线粒体DNA的新年代学研究结果的支持。科学家们也证实人类线粒体基因组表现出一定的分子进化复杂性，这需要在线粒体人类分子进化的研究中使用复杂的遗传分子模型。（生物谷www.bioon.com）
生物谷推荐原始出处：
The American Journal of Human Genetics，Volume 82, Issue 4, 895-902，Phillip Endicott，Simon Y.W. Ho
A Bayesian Evaluation of Human Mitochondrial Substitution Rates
Phillip Endicott1 and Simon Y.W. Ho1, 2,
1 Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
2 Present address: Centre for Macroevolution and Macroecology, School of Botany and Zoology, Australian National University, Canberra ACT 0200, Australia.
Abstract
Accurate estimates of mitochondrial substitution rates are central to molecular studies of human evolution, but meaningful comparisons of published studies are problematic because of the wide range of methodologies and data sets employed. These differences are nowhere more pronounced than among rates estimated from phylogenies, genealogies, and pedigrees. By using a data set comprising mitochondrial genomes from 177 humans, we estimate substitution rates for various data partitions by using Bayesian phylogenetic analysis with a relaxed molecular clock. We compare the effect of multiple internal calibrations with the customary human-chimpanzee split. The analyses reveal wide variation among estimated substitution rates and divergence times made with different partitions and calibrations, with evidence of substitutional saturation, natural selection, and significant rate heterogeneity among lineages and among sites. Collectively, the results support dates for migration out of Africa and the common mitochondrial ancestor of humans that are considerably more recent than most previous estimates. Our results also demonstrate that human mitochondrial genomes exhibit a number of molecular evolutionary complexities that necessitate the use of sophisticated analytical models for genetic analyses.
