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New statistical method throws up ancestry surprises
A new way of analysing genetic variation in human populations is throwing up a number of surprises about our ancestry. Among other things, the new technique reveals a strong gene flow from northern Europe to eastern Siberia.
The work, which is partly funded by the EU, is published in the journal PLoS Genetics.
Traditional methods of genome analysis tended to focus on one part of the human genome, such as the Y chromosome, which is passed from father to son. Other techniques took an oversimplified model of heredity that did not take chromosomal structure into account.
In this latest study, scientists from Ireland, the UK and the US analysed 2,540 genetic markers in the DNA of almost 1,000 people from around the world whose genetic material had been collected by the Human Genome Diversity Project.
The results include a number of surprises. For example, the Yakut people of northern Siberia were found to have received a significant genetic contribution from the population of the Orkney Islands, which lie off the coast of Scotland. Orcadian genes also showed up in other East Asian populations, namely the Han of northern China and the Hezhen, another north-east Asian population. From this the scientists conclude that there must have been a period of gene flow from northern Europe to east Asia.
The study also shed light on the peopling of the Americas, as the results suggest that the native populations of north and south America have different origins. The researchers explain this by suggesting a scenario involving multiple waves of migration. In their proposed scenario, the population which first colonised North East Asia also crossed the Bering Strait and eventually made it to South America. This population was subsequently replaced by a population more closely related to modern East Asians. These people also successfully crossed the Bering Strait and contributed to the ancestry of the native North Americans.
'Our technique enables us to identify more subtle details about genetic contributions than other methods,' explained Dr Garrett Hellenthal of the University of Oxford, one of the authors of the paper. 'By incorporating the inheritance of 'blocks' of DNA between generations, rather than just individual genes, it captures a panoramic view of the sharing of patterns of DNA across the entire human genome. This allows us to consider a vast number of possible colonisation scenarios - not just the ones people have already thought of - and use an algorithm to determine the most likely migration routes.'
In the future the scientists hope to expand their method to encompass datasets with over 500,000 genetic markers. In this way they hope to be able to reconstruct human migration patterns in unprecedented detail.
'Humans like to tell stories and amongst the most captivating is the story of the global spread of modern humans from their original homeland in Africa,' added Dr Daniel Falush of University College Cork in Ireland. 'Traditionally this has been the preserve of anthropologists but geneticists are now starting to make an important contribution. However, genetic evidence is still typically analysed in the light of anthropological preconceptions; statistical techniques help us to see things more objectively.'
EU support for the research came from the EU-funded POLYGENES ('Identification of common genetic variants that affect the risk of breast and prostate cancer') project, which is financed through the 'Life sciences, genomics and biotechnology for health' Thematic Area of the Sixth Framework Programme (FP6).
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Data Source Provider:Public Library of Science (PLoS)
Document of reference:Hellenthal, G et al. (2008) Inferring human colonization history using a copying model. PLoS Genetics, doi:10.1371/journal.pgen.1000078.
Subject index:Coordination, Cooperation,Life Sciences,Medicine, Health,Scientific Research,Social Aspects
Programme Acronym: MS-IRL C , MS-UK C , FP6-LIFESCIHEALTH
Record control number (RCN):29474