Can I do a DNA confirmation without triangulation where the relationship is 3C1R?

Question

My Mom has a good match for which the paper record and the amount of shared DNA suggest that the 3C1R relationship is accurate. But I can't find anyone on GEDMatch to triangulate with who is also on WikiTree or who has a tree I can look at. Thanks!

Comments

How good is this DNA match?

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Largest segment = 18.2 cM
Total of segments > 7 cM = 26.5 cM
2 matching segments

The amount of shared DNA is within the probability of what is expected with 3C1R. The match is my 4th cousin, with no shared DNA between me and her; thus I can't triangulate using myself.

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Thanks. I asked because I have a match with a 3C1R that I think is convincing, even though it's not fully triangulated, but my match (75 cM on 7 segments) is well above the average for a 3C1R, and yours is well below that average. Unfortunately, there's no way you could claim a special case for "confirmed by DNA" based on the kind of result you report.

PS - With my 3C1R match, there's a also a three-way match with another cousin, but the three-way match is too short to claim as triangulation.

PPS - If you had a match with this cousin, that would not be a basis for triangulation. A triangulated match has to be with a person on another branch of the family tree, not a parent-child pair or a pair of siblings.

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Thanks, Ellen. I thought about your last point after I had posted. I'll wait for some as-yet unknown cousin to pop up for the triangulation.

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Ellen is correct, I did a successful triangulation with 2 cousins compared to my kit. Then a second successful triangulation with the same 2 cousins compared to my Mom's kit, which yielded a different chromosome comparison. My Mom and Dad both have this line so it's been very interesting to see how the DNA piles in, what I received  form each.

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Ellen, for what it's worth, between my own, my brother's, and my wife's tests on AncestryDNA, I've identified over 50 3C1Rs, and the highest I've seen so far is 55cM, with 4 segments. There's also a  5 segment case with 51cM, and that's the maximum number of segments.

My wife also has a "double 3C1R". My wife is related to BOTH parents of one of the match's grandparent. THAT one is 118cM, on 7 segments.

SO it could be that (1) GEDmatch cMs just come up higher than AncestryDNA (10cM or 20cm higher isn't unusual), if your 75cM is a GEDmatch number, (2) your match is just an especially high outlier, or (3) there's some endogamy in the mix.

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I do most of my triangulations using 23andME matches, since they show us the segments and it is so easy on that site. However, there are not as many testers there as on ancestry.com but I am able to get hints from "Thrulines" on ancestry.com about new cousins that might work. Then I write them using the ancestry.com messaging system, and sometimes I can pursuade them to upload to GEDmatch and use the DNA data that way

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@Frank Stanley:  Variability in DNA matches starts looking more pronounced around the 3C distance and beyond. My sister, two first cousins, and I are all this man's 3C1R cousins. Our four DNA matches with him are (1) 17 cM on 1 segment, (2) 38 cM on 4 segments, (3) 60 cM on 4 segments, and (4) my match of 75 cM on 7 segments.

Answer 1

Sorry, Orin. The cutoff is third cousins. 3C1R can't be used. Keep looking and waiting.

Comments

And you wouldn't have been able to triangulate with both you and your mother being 2 of the 3 matches, since triangulation requires:

"At least three distant cousins (each one related to each of the others more distantly than third cousin) must share the same segment of DNA that is at least 12 cM."

As more individuals test and upload to GEDmatch hopefully you'll eventually find a triangulation situation in the future.

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Agreed, but to be fair, they're really not very specific in the instructions - they don't talk about "removeds" at all.

In my book, for example, 2C2R has the same average DNA as a 3C, so that's fine, but a 2C3R should NOT be OK. Similarly, half-2C2R and half-3C should NOT be OK.