05 December 2013

Family Tree DNA improvements

If you've taken the Family Finder test at Family Tree DNA you'll likely be interested in a great capability just added. As explained by CcCe Moore in an article on her Your Genetic Genealogist blog:

Added the ability for a user to download chromosome browser data for all of their matches. This new option is towards the top right side of the chromosome browser page and will be in Excel format.
You click on "Download All Matches to Excel (CSV Format)".

I got over 8,000 segments identified, all with at least 500 SNPs matching. The column heading were NAME, MATCH NAME, CHROMOSOME, START LOCATION, END LOCATION, CENTIMORGANS, MATCHING SNPS.

I found it easier to manipulate the data when in a spreadsheet, and identified a few instances of people matching on over 10 centimorgan segments I hadn't found before.

I looked at the correspondence between centimorgans and matching SNPs. There are a couple of outliers, (3.25 centimorgans and 6600 SNPs), (28.68 centimorgans and 4229 SNPs), and some intriguing structure with most points falling on a broad diagonal, and a distinct nearly vertical branch.

It turns out the nearly vertical cluster in the graph above is entirely composed of matches on chromosome six, from starting position 25.6 million to ending position 33.5 million. This area contains the major histocompatibility complex which is involved in the immune system. See this article by Ann Turner who comments that "from a genetic genealogist’s perspective, similarities in this region may be too general to have utility in identifying recent relationships."

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