If you’ve taken an autosomal DNA test at 23andMe, AncestryDNA, or Family Tree DNA, you likely have a long list of genetic cousins. After sequencing portions of your DNA, the testing company compares your results to the results of other test-takers in its database. If you share enough DNA with another test-taker in the database, you’ll see that person in your list of matches.
The company evaluates how close you might be to another test-taker based on the amount of shared DNA. See the image for a sample list of AncestryDNA matches (with usernames blurred for privacy).
In this guest post, Blaine Bettinger, DNA expert and author of The Family Tree Guide to DNA Testing and Genetic Genealogy, shares a quick tip for identifying your DNA matches with the best chance of aiding your research.
For test-takers with ancestry in well-represented areas (such as Europe), the list of genetic matches may be thousands of people long. A few of those matches might be close, but most will be distant matches who share just a small segment of DNA. How should you process all those matches? Which ones should you focus on to attempt to find your common ancestry?
Focus on your closest matches first to increase your chances of finding family members and learning more about your family tree. If you’re lucky enough to have a predicted second cousin or closer, review that match’s family tree (if the match has provided one) for familiar names or places from your own family tree. Since the relationship is so close, you may only need to build his or her tree out for a couple of generations.
If the match doesn’t have a family tree, you might be able to build one for them or contact the match and ask for one.
What do I mean by your “closest” matches? Simple: The ones with whom you have an estimated relationship of fourth cousins or closer. You have a pretty good chance of finding common ancestry (such as a great-grandparent) with second cousins or closer, and a decent chance of doing the same (i.e., finding a shared second or third great-grandparent) with predicted third and fourth cousins. Beyond predicted fourth cousins, however, you’ll have difficulty finding a common ancestor. In most cases, you’ll only want to pursue these more distant matches if you have additional concrete evidence that you share ancestors.