Thursday, May 15, 2014

Using Gedmatch "one to many"

For autosomal DNA matching, Gedmatch offers a feature which allows you to see where your autosomal DNA matches others who upload their results. Gedmatch takes uploads from, FTDNA, and from 23andme, so even if you only test with one company, as many do, you can see many matches to your DNA segments from people who tested with the other companies.

It is very easy to use this feature, and it is worth checking back every few weeks for the new matches which are uploaded. The moniker and email for the match are sometimes helpful, yet ofttimes not helpful at all--really attempts by the test subject to obfuscate his or her identity. The best scenario, and it is occurring more and more often, is that the match has uploaded a gedcom, which is worth way more than a name. After all, we researchers are looking for the match's grandparents and beyond. It is genetic history that is of interest in this game.

If a match seems useful, ways to look further are to check the match's list of matches (click on "L"). The individual that you match may not list his or her name, but may have a match within one or two generations who has done so. That is quite valuable, and worth working with to find clues to creating the tree for the match (an important step in finding the common ancestor). Another step is to find the chromosome segment where you match, and then to find the others who match (triangulation), which is another feature on gedmatch, and discussed elsewhere on this blog.

You will probably also want to click on A, which shows you the chromosome segment where you match the other tester. You can make a note of this segment and then check for matches elsewhere on gedmatch or on HIRsearch to that particular segment. Because the segment match may be on either side of your ancestry (paternal or maternal), the fact that it matches a third party may not reflect a true match. It could be coincidental, and the match may be to  the parent who would not match the second party and yourself. This is where triangulation is of great help, because gedmatch will show you where your matching segments of chromosome overlap with more than one other match, and the information on the utility will even indicate for you that this is likely an indication of shared ancestry.

Now what can you do with shared ancestry? Ideally the people you match with have more information on their ancestry than you do, and you can see who might be the common ancestor, or at least the direction that the ancestry will have to be. Less ideally, you may have more information to work with. Geography, names, anything can be helpful. You should note all of the information you receive (a good place to do it is on a digital family tree--easily revised) so that it can come in handy when you get more information, which is likely to happen given the recent surge in autosomal testing.

Don't forget that if you get intrigued by a chromosome segment that you can easily see matches who also share that segment by uploading your data to HIRsearch.

The site has many features. It may take awhile to tackle all of them. I do recommend trying this one, and taking the time to figure it out. It is one you are likely to return to and to find useful as you try to establish your genetic ancestry, which, as we all know, may just not quite match the family history you have on paper.

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