DNA Triangulation Made Easy: A Case Study

One of the things that has absolutely fascinated me are the new doors opened up by looking at DNA.  As I mentioned in my "Get them to say yes" presentation, DNA has helped me identify new branches of my family that can then be confirmed via paper trail, photos, and family stories.  DNA suggests new places to look.

I received an e-mail a few months ago addressed to my 3rd cousin 1x removed, Barbara.  Barbara had recently agreed to be tested as a part of a Facebook plea asking for members of a certain branch of my family to test.  The reason I was asking for more people to test is that I'm a huge fan of DNA Triangulation.

DNA Triangulation uses autosomal DNA tests (in this case FamilyTreeDNA's FamilyFinder test) from multiple known relatives to help identify which genetic lines they share with previously unknown genetic matches.  If Saul (a previously unknown person) has a close match with my known relatives David, Sherry, and Matt, then the relationship is probably along the ancestral lines that David, Sherry, and Matt have in common.

The reason to use an autosomal test (aside from the fact that it is the least expensive test) is that autosomal tests look at DNA from both of a person's parents so they can pick up relationships that are not straight paternal line (Y-DNA) or straight maternal line (mtDNA).  So if your mother's father's aunt is the connection between two people,  a FamilyFinder test may pick it up (at least until you get past the 5th cousin level, in which case it fades into the background of random chance or with Jewish endogomy you hit the "we're all Ashkenazi Jews" wall since we're more or less all related to each other).

So, I took one branch of my family, Harry Cooper and Martha Allen, and asked if the oldest living descendant of each of their eight children would be willing to take a DNA test.  I didn't get someone from every branch (yet) but a good number of people agreed.

Harry Cooper and his wife Martha Allen Cooper

The results from one of the branches, Barbara, had her results come back on October 14th. An e-mail showed up in my inbox the very next day.  Apparently Barbara's results had her listed as a 3rd-5th cousin match with him and as a 2nd-3rd cousin match with his mother!

During our e-mail exchange he sent me the results of his mother's chromosome browser results with a number of my known relatives.  Barbara, David, and Stuart are all first cousins to each other.  This enabled me to narrow down the shared genetic line to the ancestors shared by all three people.

As you can see, all four people share a match on chromosome 21, however there are three other spots where three of the four individuals share a segment of DNA that is greater than 5cm.

Okay, what does it tell me?  Does it tell me that Barbara is definitely related to this man's mother?  Probably not yet, but it does make me want to take a closer look at the ancestors that David, Stuart, and Barbara have in common.

Following the DNA Triangulation method, my next step would be to get descendants of the lines that David, Stuart, and Barbara have in common to test.  One of the lines these three have in common is Halperin.  If, for example, I test known Halperin who I can link to these three via a traditional paper trail and the match with these new people continue, then I know to take a closer look at the Halperins.  If there's no match with Halperins, but a match with known relatives who are Isaacsons and not Halperins (David, Stuart, and Barbara are descended from both), then I know to take a closer look at the Isaacson line.

What do you think?  Does this technique seem useful, or is it an expensive waste of time and money in Jewish populations since we're endogomous to begin with?  This is such a new science; we all have so much to learn!