I was asking about triangulation in the Genetic Genealogy Tips and Techniques Facebook group and I was fortunate enough to have Blaine Bettinger of The Genetic Genealogist answer my question. I’m pretty sure this is the equivalent of having Mozart answer your question about scales, and it’s probably not the first time he’s had to answer a basic question about triangulation either. I had read somewhere that using parents as one leg of your triangle is not a good thing, and since I often use my great-aunt as one of my legs, I wanted to know if I was totally messing things up and setting myself up to chase after non-existent triangles as in the case of S.R. and F.D. that I wrote about in my post Triangulation.

Why wouldn’t you want to use a known relative? Obviously the advantage is that you’ve already got 2/3 of the triangle figured out as you know the family tree of both you and your relative (hint: it’s the same tree). However, the disadvantage is that this information is very limited. The closer the relationship between you and the other people triangle, the further you are away from the common ancestor that all three of you share. Remember how triangulation is like a three-legged stool? As Blaine told me, “You can certainly use your great-aunt, but of course you and your great-aunt only go back to your great-grandparent. This is helpful to narrow a match down to this line, but it’s more of a two-legged stand than a triangulation tripod.”

What are we to do with this information? Don’t use a known relative when creating triangulation groups, instead use the information to figure out which branch of your tree your common ancestor is going to be on. Another member of the group gave the suggestion to check (on Gedmatch) the genetic distance between your two matches by running a ‘one to one compare’ on both their kits. They should be about as genetically as far apart from each other as you are to each of them. The further apart the legs of the stool are from each other, and the more equally apart they are from each other, the more stable the stool will be. If you do find matches that are close, this means that they can narrow down which branch of their tree the common ancestor will be found on. Then find another match to complete your triangle (heck, why stop at three?)

Remember P.B.? I found her cousin, R.S., On Ancestry. This cousin had a lot of information about that particular branch of the family, where they came from, immigrated to, and information they were still looking for. This was quite a boon. However, the common ancestor I am looking for is further back than the ancestor that P.B. and R.S. share. G.K. and P.B. are genetically the same distance apart from each other as they are to me (4.8 generations, according to Gedmatch), so whatever G.K. can tell me gives me more data to add to my search. Even though there is no overlap between P.B. and G.K’s trees, I’ve still collected some useful data. P.B. and R.S.’s ancestor came to North America from Ireland during the potato famine. G.K. Is Irish. Already I am further ahead than when I started, because I didn’t even know I had any Irish ancestry. Now to find more DNA matches that triangulate with P.B. and G.K. I’m going to take a shortcut by investing in Tier 1 utilities on Gedmatch, which will produce triangulated matches for me at the push of a button.