Triangulation

Made a connection with my first good case of triangulation on chromosome 15 today.  Contacted a recent match at 23andMe (Robert) and began looking at the possibilities.  What I discovered was that we matched at the same point as a known relative - and therefore we have triangulation!

Robert matches both me and my mother at the same location on chromosome 15.  23andMe rounds the start and end points to be as follows: for both my mother and me, the shared start point is 81000000, for me the end point is 89000000 and for my mother the end point is 90000000.  Not much of a difference, but Robert shares a slightly longer segment of DNA with my mother (10.4 cM) than with me (9.3 cM).

23andMe Segment matches with Robert, I'm green, mom's is blue

Robert also has his results uploaded at GEDMatch, and I was able to confirm the results, the start and end locations for matches with me are as follows:

Robert's results for the start and end location of the match with mom was nearly the same :

But what really got me excited was Robert's match with a known relative on my mother's side, Mildred.  The results for Robert's match with Mildred :

Mildred is my maternal 1st cousin 3 times removed.  Her grandmother was the half-sister of my 2nd-great grandmother, Ida Davis.  The common ancestor between Mildred and myself is Mary Ellen Swafford (1854-1932).

This is how I match with Mildred (note chromosome 15) :

My mother matches Mildred even more (note chromosome 15) :

Because Robert matches on the exact same chromosome in the exact same location to not only me, my mother and Mildred, we have triangulation on this spot, indicating that the match is Identical by Descent, rather than Identical by Segment.  Anyone that matches all of us at this same chromosome and segment must be related through the same line.  Because the common ancestry between myself and Mildred is Mary Ellen Swafford, so the DNA either came from her or one of her ancestors.

Robert is predicted by 23andMe to be a 3rd to distant cousin.  We share just one segment and 0.13% of our DNA.  GEDMatch predicted that the estimated number of generations to the MRCA is 5.2 generations.

One of the surname's in Robert's ancestry is Thacker, and there is a Thacker-Swafford connection, but in the correspondence so far, the names do not match up.  Robert's tree is just getting started, and I hope that by sending my contact an outline of Swafford ancestry we can find a common name. My thought is that the connection is further up line from Mary Ellen Swafford.  She has several female ancestors with unknown maiden names.


The DNA game is an exciting one to play around in, and I appreciate any suggestions or tips.