Friday, 28 December 2012

Searching for matches with the same DNA segment


This is an exercise you could do with any of your matches on FTDNA's Family Finder. 

Supposing you and one of your matches share a segment of chromosome 8 in common. It follows that other people who match both you and your match on exactly the same segment of chromosome 8 probably inherited it from the same common ancestor. So here is how to use the Chromosome Browser utility on FTDNA to search for additional matches on the same segment of a given chromosome (Gedmatch does the same thing, but not everyone has uploaded their results to Gedmatch so it's useful to do it on both websites).
  1. Hover over the Family Finder tab, and click on Chromosome Browser from the drop down menu
  2. in the list of names at the bottom left, click on your original match and use that as a reference point (you'll have to advance the pages by clicking on the arrow to the right until you find them, then click on the empty box to the right of their name). The matching segment on Chromosome 8 will appear in the diagram to the right. This is now your reference guide.
  3. Go back to Page 1 and click on each of your matches in turn - I have 181 matches so it takes me about 10 minutes to go thru each one.
  4. You can only compare a maximum of 5 matches at a time, and because you will be leaving your reference match up all the time, this means you can only compare 4 additional matches at a time. So, click on the boxes to the right of the first 4 names. Check to see if any of them match on or around the same segment on chromosome 8. Make a note of the name of any that do. 
  5. To remove the matches and compare the next 4, first go up to the top left, and click on the coloured box beside each of the 4 names below your reference match - the names disappear.
  6. Now click on the next 4 matches (back to the bottom left). 
  7. Keep repeating this until you have gone through all your matches. 
  8. Hopefully you will find several that are pretty close matches to this segment. If you and your original match have names in common, then probably these people will have received the same segment of Chr 8 from the same common ancestor to you all.

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