Should chromosome 23 be used for autosomal DNA triangulation?

Question

The GEDmatch tools compare chromosome 23, but I'm wondering if matches seen on chromosome 23 should be used for DNA triangulation, or whether the threshold should be higher than 7 cM?  For example, see this report where it almost reaches 7 cM, so would fall below regardless, but as an example.  Here are the parties of the match on 23:

Janice Samples GEDmatch T721693

Sonya Wickham GEDmatch M065598

Susan Melissa Foster GEDmatch A798497

Elizabeth Mundy Foster GEDmatch A256246

Carole Ann Foster GEDmatch A711938

The first three share 6.0 cM, so since on X, is that enough (not being over 7.5 cM normal threshold)?

Answer 1

Because x-chromosome (Chromosome 23) information is inherited more restrictively than any other, quite the opposite is true. It's much harder to triangulate on Chromosome 23 than on our other 22 Chromosomes. This is one reason why two distant male cousins who match via x-DNA are not required to triangulate. If anything, the threshold for triangulation should be lower for groups using the x-chromosome. We are not looking for DNA Proof in absence of other evidence, but DNA Confirmation of relationships already documented by a paper trail.

Comments

In response to your revised question, I should add that WikiTree DNA Confirmation Rules are as specific as they are simplistic. The DNA Confirmation Rules do not specifically address all x-chromosome matches over a smaller than 7cM segment of DNA, nor do they address the significance of triangulating with more than three relatives. Those rules were established only for simple DNA Triangulations.

In my opinion (but not that of WikiTree), it could possible to triangulate with slightly less than 7cM on the x-chromosome. In this particular case, the difficulty of triangulating with the five individuals listed lies in the close relationships between the first two profiles and between the last three. True triangulation would require that three of the matching persons should be more distantly related than these. Finding another matching cousin, not closely related either to the first two, or to the last three, would cinch it for me. But then again, that's just my opinion, which doesn't represent that of WikiTree.

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I agree with Bill.  Triangulation is three separate independent descendants of the ancestor you are trying to prove.  DNA matching evidence can easily be misleading if you use the tests of close relatives to try and prove a distant ancestor, since people often focus on the fact that several close matches share a segment.  

I often see this where people will try and argue that they have a stronger case that a segment was passed down from specific great-great-grandparents because a mother and her two children each share the segment.  This gets people into trouble.  The focal point is to use the DNA evidence to support the great-great-grandparent's relationship to the testers.