Сибирское отделение РАН
Изменчивость генома человека
In this presentation I will discuss the phylogeography of human mtDNA diversity worldwide, with a specific emphasis to Eurasia. First, the question of the topology of the human mtDNA tree will be addressed in brief, showing that by now, the main aspects of it are reasonably well understood. This offers a powerful guideline to orient mtDNA classification towards a reliable phylogenetic analysis, identification of MRCAs for most of the branches of the tree. Thus, one of the central aspects is to identify “internal nodes” of the tree. That, in turn, allows to use molecular clock and coalescence calculations to get at least an educated guess when did mtDNA lineage clusters start to diverge, expand etc. A detailed knowledge of the phylogeography of the main macroclusters – trunks of the tree - such as L, M and N, and that for many derived clusters such as U, T, J etc., allow now to get insight into prehistoric population movements, whereas the reconstruction of their detailed topology is often helpful in the understanding of a possible time scale involved. One may add here that the same approach is now well advanced also for the Y chromosome analysis and, in tandem, these two uniparentally inherited genetic systems offer a hitherto unapproachable means to follow, in parallel, our paternal and maternal past.
The last five years have witnessed a lively debate of how to interpret an increasingly more complex data set for mtDNA lineages in terms of the genetic history of world populations. This debate is still going on. Most of researchers agree now that there is a very strong evidence that the MRCA for all extant maternal lineages derives from sub-Saharan Africa, with a time depth around 150,000 years before present. Less clear is a problem when a massive colonisation of the other continents started. Yet, as far as Eurasia and Australia are concerned, mtDNA diversity–based coalescence calculations suggest a time scale around 50,000 – 70,000 BP as the beginning of expansion of the main lineage clusters, such as, e.g., M and U for Eurasia. This estimate is in a reasonable agreement with the existing archaeological evidence. It is particularly important to notice that this coalescence-based timescale reflects the emergence of a profound, still existing difference between western, eastern and southern Eurasia.
Recently, a much better geographic coverage and larger sample sizes made it possible to go significantly further and to analyse individual mtDNA lineages clusters regionally. It allowed to reveal that the “core” mtDNA haplogroups are far from uniform in several different meanings. First is that the individual subclusters thereof are spread quite unevenly. Secondly, and that is perhaps even more important, individual subclusters display coalescence ages which differ profoundly from that estimated for the parent cluster as such. Thirdly, the coalescence age for individual subclusters can be rather different for different geographic regions. I will finish my presentation discussing phylogeography/coalescence pattern of some typically western Eurasian mtDNA lineage clusters in order to demonstrate that although their time depth may well belong to early Upper Palaeolithic, they do consist (can be split into) numerous, likely monophyletic, subclusters of much more recent origin/expansion. While most of such subclusters, even belonging to phylogenetically different clusters, suggest expansion during Mesolithic or later, there is a phylogeographically characteristic set of mtDNA lineages, revealing expansion around the peak of the LGM in eastern Eurasia, in contrast around Mesolithic in northwestern Eurasia. In sum, arhaeogenetics starts to emerge and what is needed now is just more work.
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Дата последней модификации: 06-Jul-2012 (11:44:54)