Currently, there is a spirited debate taking place amongst the genetic genealogy community over the “realness” of matches based on tiny segment size. First, Roberta Estes wrote about how she used small segments, some as small as 1 cm to help identify a common ancestor. She then clarified her methods and rationale here. In response, Blaine Bettinger contributed his research on small segments that are Identical by Descent (IBD) vs Identical by State (IBS), as did CeCe Moore. The subject has been pounced upon by the community, with views ranging from ‘small segments are worthless and random’ to small segments are ‘representative of deep population similarities’ to proof positive of common ancestry. Amidst the hubbub what is clear is that there is a lot of confusion and misinformation being spread among the rank and file, and a lot of work to be done, and published by those conducting large scale multi-generational studies.
When testers receive their results from FTDNA, their matches are classified based on how closely they are likely to be related. This classification is based upon the amount of shared genetics and measured in centimorgans. Genetic genealogist John Walden has produced a chart that every DNA tester must become familiar with:
Identical by Descent (IBD) means the DNA shared between matches comes from a common ancestor. Otherwise, a match is considered Identical By Structure (IBS), or mimicking IBD and not inherited from a common ancestor.
FTDNA won’t show a match that doesn’t share a segment of at least a 7.7 cm and a total of 20 cm in common. Still, there is a 50-50 chance such a match might be false. It is only at 10 cm that you can be fairly confident you share a common ancestor. As more research is being done, including results from trios of parents and children and Ancestry’s investigation of ‘pile-ups’, researchers are continuing to improve our knowledge of which matches are statistically likely to be real.
Unfortunately, this doesn’t stop some, especially new folks, from investigating matches at the 1 cm segment mark. At Gedmatch.com it is possible to lower the search threshold but the owners warn users, “To qualify as a ‘match’ in the genealogical time frame, results must have a largest Autosomal segment that has at least 700 SNPs and be at least 7 cM. It must have BOTH.”
DO NOT DO THIS
In my own experience, I received a mass email from Dr Hester, who has clearly invested a great deal of time studying his FTDNA matches. His intent is to map his chromosomes so that he may determine which segment has been inherited from which ancestor.
Dr Hester has gone through his match list and for his entries, clicked upon the In Common With tool and then used the Chromosome Browser to compare chromosomes. On his website, he has then provided screen shots of how his matches share DNA, identified the tester and putative ancestor, and classified matches in groups he believes are descended from particular individuals in his family tree. He has urged his matches to conduct similar studies.
When my name is clicked upon, I see this:
First of all, it is not cool to list the full names of your matches without permission, Second, if you note the upper left hand corner, he has reduced the segment size to 1 cm. Dr Hester goes on to write,
“This is a rather small group of only 3 matches in common with Lori A. plus McConnell as was shown as an ancestral name for Lori. The matching segments for Lori A are all very short indicating distant and possibly multiple common ancestry. For all of these matches the common ancestry has been quite a mystery.
Myhrvold is Norwegian, so the matches with him may involve a settler of New Sweden, whose descendants may have moved to Pennsylvania. But as shown in the lowest rows, the match with him on chr 22 is presumed to have been inherited by the author over Margaret Swinderby born 1578 in Copenhagen, although the author’s Christopher Randall and/or his wife Johanna widow Norman may have been from New Sweden too.
Rayburn shares quite a bit of DNA with the author: the match on chr 11 has been established elsewhere on this page as Andrews DNA. And both Lori A and Rayburn share one typical segment of Taylor DNA on chr 12, while Stevens shares another.”
That sounds great except for one small problem: the people Dr Hester and I both have in our match lists, or In Common With aren’t necessarily related to each other and lowering the threshold to 1 cm is only going to lead to wild goose chases. As members of my close family have tested, I know the matches he has grouped me with cannot share a common ancestor with me. Dr Hester is a maternal match. RAYBURN is a also a maternal match but MYHRVOLD is a paternal match.
Dr Hester is gambling heavily on the validity of the In Common With tool combined with very low segments. Yes, we match him. Yes, RAYBURN, MYHRVOLD, and I somehow match, but how we match each other must then be determined through triangulation and traditional genealogy. In this instance, I known I match RAYBURN and MYHRVOLD on entirely separate lines and these miniscule matches Dr Hester is reporting are IBS, or junk.
To make matters worse for Dr Hester’s method, when I compare our results in Genome Mate, I see that he and I share no matches at all above the 8 cm default I have set.
Although I contacted Dr Hester last summer and explained we cannot possibly match in the manner he has determined, he has let the incorrect information stand. Doubtlessly, he is continuing to take screen shots of his matches, lower the chromosome browser setting to 1 cm and use the In Common With tool in a way that won’t accurately advance his work.
We all must start somewhere and we all make mistakes. Genetic testing is the bleeding edge of genealogy and our knowledge and methods are evolving at a dramatic rate. Experts like CeCe Moore are doing their best to educate us and share their knowledge and resources. It is up to the rest of us to read, listen and learn.