DNA Q&A: Using DNA to Find Relatives

By Blaine Bettinger

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Not quite sure what to do with those AncestryDNA results or anxious to find long-lost family members? DNA expert and author of The Family Tree Guide to DNA Testing and Genetic Genealogy Blaine Bettinger offers some advice on how to successfully use your DNA results and matches to find distant cousins and other relatives.

Jump to a specific question:

Q: I have a long list of DNA matches. Now what?

Q: What are DNA surname projects? Should I join one?

Q: How are adoptees related to their DNA matches?

Q: I have a long list of DNA matches. Now what?

A: If you’ve taken an autosomal DNA test 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.

A sample list of AncestryDNA matches (usernames blurred for privacy).

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. So how do you decide where to begin?

Focus on your closest DNA matches first.

This increases 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.

What does “closest matches” mean?

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.

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.

Q: What are DNA surname projects? Should I join one?

For the full version of this article click here.

A: With the exciting technology of DNA testing, genealogists can make research strides by examining their surnames in greater detail than ever before. Surname projects are collaborative efforts using the results of DNA tests to study the origins of a surname and how people throughout the world with the surname are related. Thousands of these projects exist, some with hundreds of members. One or two administrators typically run a surname project, organizing results, sharing information and recruiting new members to be tested, usually with the same testing company.

Here are six ways surname studies can help you find answers to your genealogical quandaries:

1. Test relationships among similar surnames.

As a surname project accumulates members, the Y-DNA results often begin to cluster into groups of closely related individuals.

2. Connect with genetic cousins.

Surname projects can take advantage of that ability and connect you with other members who might be closely or even distantly related.

3. Break through brick walls.

Surname projects offer the opportunity to break through brick walls in the paternal line.

4. Prove or disprove a theory.

You can analyze a wide variety of genealogical theories through surname projects.

5. Uncover a place of origin.

The clustering of Y-DNA results in a surname project can uncover clues about country of origin, especially if your results indicate your Y-DNA is closely related to that of immigrants from a particular place.

6. Confirm traditional research.

Genetic genealogy works best when combined with tried-and-true traditional research in historical records. Participating in a surname project can help you confirm what you’ve learned from those resources.

A version of this article appeared in the September 2010 issue of Family Tree Magazine.

Q: How are adoptees related to their DNA matches?

For the full version of this article, click here.

A: A close match is the goal of most adoptees who turn to genetic genealogy testing, as this can help reveal genetic heritage. All the testing companies now provide the total amount of DNA (measured in centimorgans, or cM) shared with each genetic match, information that can be vital for determining the genealogical relationship. One you know the number of shared centimorgans, your first stop for estimating a relationship is the International Society of Genetic Genealogy’s (ISOGG) Autosomal DNA Statistics page.

Remember that these figures are the average amount of DNA that relatives will share; thus, the actual amount of shared DNA will likely vary. About half the time, the amount of shared DNA will be more than the average, and about half the time the amount will be less than the average. Additionally, if the two relatives are related through more than one recent common ancestor, the relatives could share more DNA than expected.

According to AncestryDNA, you share 1,622 cM of DNA with your close match. The closest category on the ISOGG’s chart is “Grandparent/grandchild, aunt/uncle/niece/nephew, half-sibling,” relationships predicted to share 1,700 cM, or 25 percent of their DNA. The actual and estimated figures are close enough to be very confident that you and your match have one of these relationships, provided that you aren’t related through multiple ancestors.

A version of this article appeared in the May/June 2016 issue of Family Tree Magazine.

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