4th Cousins Matching 2 Segments >12cM [closed]

Question

Hello,

As I understand it, according to Wikitree's DNA relationship confirmation instructions, DNA matches beyond 3rd cousins are traditionally established via triangulation instead of through one-to-one comparisons.

Correct me if I'm wrong:

• Confirmation through triangulation normally involves three relatives beyond 3rd cousins who all match on the same DNA segment of 12cM or greater.
• In contrast, one-to-one comparison confirmations involve just two individuals who are up to 3rd cousins, and if one matching segment of 12cM or more is found between them, then it is considered sufficient to officially confirm their DNA relationship.

However, my question is, if you have a 4th cousin who matches you on not one, but the same two segments of 12cM or greater, is a one-to-one comparison not enough to establish DNA relationship confirmation?

I have a 4th cousin 2x removed who matches me on the same two DNA segments of the same chromosome. The smallest of the two matched segments is greater than 15cM. Additionally, I have three DNA test kits for myself, tested all three against that of the aforementioned 4th cousin, and confirmed both large matched segments with all three of my tests. So, in this case, are not two large matched segments just as good as a triangulation for establishing official DNA confirmation for relationships beyond 3rd cousins? Or should the DNA relationship be listed as Confident instead of as Confirmed?

Thanks!

Comments

In reference to the second bullet point

In contrast, one-to-one comparison confirmations involve just two individuals who are up to 3rd cousins, and if one matching segment of 12cM or more is found between them, then it is considered sufficient to officially confirm their DNA relationship.

Not according to the confirmation help page which says

Is the relationship of the two test takers, through traditional genealogy, third cousin or closer, and are the expected average DNA sharing amounts and the predicted relationship range in  approximate agreement with the relationship? 

You would need much more than just one 12 cM matching segment for a one to one confirmation with 3rd cousin or closer

---

Thanks,

So, the range also has to match. In my case that's another point in favor of this being a confirmed match between two 4th cousins. The other test taker is my 4th cousin twice removed and the predicted relationship (MRCA) is in agreement on all three of my tests: "4.2."

Answer 1

Hi Paul,

I'm not a DNA expert, but I'm learning more and more as I go along. My understanding is that your 2 bullet point statements are correct. And it makes sense to me that a line had to be drawn somewhere to say that additional evidence is needed to support DNA confirmation for more distant relationships. So here at WikiTree we have triangulation as criteria for >3C auDNA confirmation.

My oversimplified view of triangulation is that we're essentially trying to assign ancestors to a particular segment. If we have 3 or more potential distant cousins (>3C) that all share a common segment with each other and they all have evidence of the same potential MRCA(s) in their trees, then we are likely correct in attributing that particular segment to the MRCA(s).

If 2 potential distant cousins that share a common segment, also share another common segment, that may be a stronger indication that the 2 individuals are actually related. But IMO, it doesn't provide any additional evidence to support that a particular candidate ancestor is indeed the correct MRCA, which is what we're really trying to do at this point.

Also keep in mind that while the MRCA(s) are only 4 generations away from 3rd cousins, the MRCA(s) are 5 and 7 generations away from 4th cousins 2x removed.

In this case I believe the relationships should be marked as "confident" vs "confirmed with DNA" (assuming that you have other sources that support "confident" for each of the parental relationships in question).

Comments

Thanks,

I marked it confident, but another point in favor of this being about as clear a confirmation of relationship as can be is that according to our family trees, the other test taker in question and I are fourth cousins twice removed. On all three of my DNA tests that I ran against hers, the outcome MRCA was "4.2."