Comments on: A Different Kind of Gene Mapping: Comparing Genetic and Geographic Structure in Europe http://spittoon.23andme.com/2008/08/13/a-different-kind-of-gene-mapping-comparing-genetic-and-geographic-structure-in-europe/ A receptacle for genetic knowledge. Tue, 06 Jan 2009 19:43:36 +0000 http://wordpress.org/?v=2.6 By: chris http://spittoon.23andme.com/2008/08/13/a-different-kind-of-gene-mapping-comparing-genetic-and-geographic-structure-in-europe/#comment-1167 chris Fri, 12 Dec 2008 00:02:31 +0000 http://spittoon.23andme.com/?p=866#comment-1167 This paper, and the others like it, use data from across the entire genome to determine genetic distances and associated techniques to best fit the data across multiple dimensions. The dimensions that do come out are not an attempt on the authors' part to create a map out of genes: these are the first two dimensions of variation in the data. They just happen to line up well to N/S and E/W axes. It is sometimes hard to believe how good the concordance is between genes and geography in Europe, but it's worth noting that this is what you would expect: neighbors are more likely to mate with each other than people on opposite sides of the continent. Thus, over time, neighbors will be more likely to be similar to one another than to people from far away. Your example of Y-chromosome haplogroup I is worth bringing up. However, on more precise examination there are different lineages within haplogroup I in different parts of Europe. I1 is found further north, on average, and I2 is found at higher frequencies in the Balkans. Most markers across the genome provide very little information (less than the Y-chromosome haplogroup I SNPs, for example) about ancestry, but combined, hundreds of thousands of markers do tell quite a lot. If you are a customer at 23andMe or have a demo account, you can see it for yourself. The new Advanced Global Similarity feature puts you in this same sort of display: https://www.23andme.com/you/globalsim/advanced/ check it out! This paper, and the others like it, use data from across the entire genome to determine genetic distances and associated techniques to best fit the data across multiple dimensions. The dimensions that do come out are not an attempt on the authors’ part to create a map out of genes: these are the first two dimensions of variation in the data. They just happen to line up well to N/S and E/W axes.

It is sometimes hard to believe how good the concordance is between genes and geography in Europe, but it’s worth noting that this is what you would expect: neighbors are more likely to mate with each other than people on opposite sides of the continent. Thus, over time, neighbors will be more likely to be similar to one another than to people from far away.

Your example of Y-chromosome haplogroup I is worth bringing up. However, on more precise examination there are different lineages within haplogroup I in different parts of Europe. I1 is found further north, on average, and I2 is found at higher frequencies in the Balkans. Most markers across the genome provide very little information (less than the Y-chromosome haplogroup I SNPs, for example) about ancestry, but combined, hundreds of thousands of markers do tell quite a lot. If you are a customer at 23andMe or have a demo account, you can see it for yourself. The new Advanced Global Similarity feature puts you in this same sort of display:
https://www.23andme.com/you/globalsim/advanced/
check it out!

]]> By: rogers http://spittoon.23andme.com/2008/08/13/a-different-kind-of-gene-mapping-comparing-genetic-and-geographic-structure-in-europe/#comment-1162 rogers Thu, 11 Dec 2008 03:48:20 +0000 http://spittoon.23andme.com/?p=866#comment-1162 I have not read the paper (yet!) but based on the map I find it somewhat misleading as there are instances where genetic similarities between populations exist that are not even remotely close geographically. Take for example the Y-chromosome haplogroup I. Its frequency among the male population between regions of southern europe and northern europe are remarkably similar. More specifically, in the north west balkans the frequency of the "I" haplogroup matches or exceeds frequencies of that found in areas of far northern europe. Perhaps this is why this region of europe was left out of the study? I have not read the paper (yet!) but based on the map I find it somewhat misleading as there are instances where genetic similarities between populations exist that are not even remotely close geographically.

Take for example the Y-chromosome haplogroup I. Its frequency among the male population between regions of southern europe and northern europe are remarkably similar. More specifically, in the north west balkans the frequency of the “I” haplogroup matches or exceeds frequencies of that found in areas of far northern europe. Perhaps this is why this region of europe was left out of the study?

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