PNAS:用于估计古代基因组年代的分子钟
美国格伦比亚大学与美国哈佛大学医学院科研人员报告了一种用于估计古代人类残骸的年代的遗传学方法。准确估计古代人类标本年代是解释古代dna分析的关键。尽管放射性碳测年这种估计标本年代的标准工具非常精确，它可能因为污染而产生偏差。Priya Moorjani及其同事开发了一种用于测定古代基因组年代的补充方法，方法是比较自从尼安德特人基因渗入到古代和现代非非洲人的共同祖先起的古代与现代非非洲人之间的遗传重组累积数量。多数非非洲人拥有源于大约5万年前发生的人类与尼安德特人杂交导致的2%的尼安德特人世系成分。假定每一代的重组率大致恒定，自从尼安德特人的DNA最初引入之后，重组的数量可以作为一个分子钟，从而推断出在一个古代基因组和当代基因组之间失落的代际数量。这组作者用基因组测序数据，对来自北美、欧洲和西伯利亚的5个古代人类标本检验了他们的方法，放射性碳测年数据为1.2万年前到4.5万年前，获得的年龄估计与放射性碳年代一致。使用以年计数的放射性碳年代与以代际计数的尼安德特人基因渗入年代的相关性，这组作者估计了历史上的代际间隔大约是每代人28年。这组作者说，这种估计符合当代西部欧亚裔的情况。
原文链接：
A GENEtic method for dating ancient genomes provides a direct estimate of human generation interval in the last 45,000 years
原文摘要：
The study of human evolution has been revolutionized by inferences from ancient DNA analyses. Key to these studies is the reliable estimation of the age of ancient specimens. High-resolution age estimates can often be obtained using radiocarbon dating, and, while precise and powerful, this method has some biases, making it of interest to directly use genetic data to infer a date for samples that have been sequenced. Here, we report a genetic method that uses the recombination clock. The idea is that an ancient genome has evolved less than the genomes of present-day individuals and thus has experienced fewer recombination events since the common ancestor. To implement this idea, we take advantage of the insight that all non-Africans have a common heritage of Neanderthal gene flow into their ancestors. Thus, we can estimate the date since Neanderthal admixture for present-day and ancient samples simultaneously and use the difference as a direct estimate of the ancient specimen’s age. We apply our method to date five Upper Paleolithic Eurasian genomes with radiocarbon dates between 12,000 and 45,000 y ago and show an excellent correlation of the genetic and 14C dates. By considering the slope of the correlation between the genetic dates, which are in units of generations, and the 14C dates, which are in units of years, we infer that the mean generation interval in humans over this period has been 26–30 y. Extensions of this methodology that use older shared events may be applicable for dating beyond the radiocarbon frontier.
作者：Priya Moorjani
