中国人群支系扩张和群体扩张研究

Although the Chinese population is the largest in size, its Mitochondrial and Y lineages are limited to a few major lineages, suggesting a history of several major population expansions. Our previous work revealed that major lineage expansions and population expansion of East Asians began before Neolithic Time, contradicting the well-accepted theory in anthropology that agriculture predated population expansions. Accurate and presice dating of when Chinese population began the major expansion and what lineages enperienced major expansions are yet to be achieved, largely due to the lack of sufficient polymorphic sites and large samples that are randomly collected without a priori criteria. The aims of the project proposed here is to estimate the time of lineage expasions and population expansions of Chinese population by analyzing the sequences of mtDNA and Y chromosomes in samples that are randomly collected in multiple regions in China. Furthermore, the ages of lineage expansions and population expansion will be estimated without ascertainment bias, based on which, possible reasons will be inferred. The accomplishment of this work would help to fill the gap of knowledge in unerstanding fine genetic structure of Chinese population, to explore the impact of climate and agriculture on population expansions, and to further our effort in investigating the origin and migration of Chinese populations.

中国人群虽然庞大，但其线粒体DNA序列和Y染色体序列归属于有限的几个支系，提示其可能是由几次主要的群体扩张所造成。我们的前期工作发现东亚人群及其主要支系的早期扩张均先于农业的产生，有悖于广泛接受的农业产生先于人群扩张的人类学理论。而究竟是什么时候中国人群开始主要扩张，主要是哪些支系进行扩张缺少准确和精确的估计。其原因在于：（1）缺少随机取样的大样本，（2）缺乏足够的多态位点。本项目主要以上述两个问题为突破口，通过对多地区的随机样本进行线粒体和Y染色体全序列分析，研究中国人群重要的扩张支系，并对各支系扩张和群体扩张的年代进行无偏估计，进而推测不同时期人口扩张的可能原因。本项工作的完成，将弥补中国人群精细遗传结构研究中的缺失环节，了解不同时期气候变化和农业的产生对人口扩张的影响，进一步完善中华民族的起源和迁徙的研究。

通过线粒体DNA、Y染色体和常染色体信息，全面解析了中国人群的支系扩张和群体扩张。1）通过线粒体DNA推断中国群体扩张。利用线粒体DNA对中国南方族群以及藏族族群进行了研究，验证了之前所发现的发生于1万3千年前旧石器时代的人群扩张。此外，发现在农业产生之后，中国人群发生进一步的群体扩张（Molecular Biology and Evolution 2013, Scientific Reports 2015 and 2016）。2）通过Y染色体标记推断中国人群扩张。对东亚地区70个样本的Y染色体进行约4 Mbp区域的测序，发现了4000余个新的SNP位点，并重新绘制了高精度的Y染色体谱系树，发现40%的中国人其Y染色体来自三个新石器时代的超级祖先于6千年前的星形扩张（PLos One 2014）。3) 通过常染色体推断中国人群扩张。我们应用了千人基因组计划的中国汉族测序信息，估算了中国人群从末次冰盛期开始（2万5千年前）的有效群体大小。结果发现，中国人群从末次冰盛期开始基本呈现连续的扩张，可以细化为三个扩张阶段（2万5千年前-1万5千年前，1万5千年前-8千年前，8千年-今；Scientific Reports 2016）。同时，本项目解析了尼安德特人的基因在现代欧亚人中的混合（Molecular Biology and Evolution 2014 and 2015）。