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Very large X-match

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  • Very large X-match

    My paternal uncle (RBG) has what seems to me to be a very large X-Match with another man, VRH, who is his double third cousin (2 shared sets of great-great-grandparents). In addition to 106 shared cM of autosomal DNA, they match on 3 segments of X, for a total of 102.72 cM on X alone. The longest shared segment is 65.36 cM. Based on what I’ve read about X inheritance patterns, of their four shared great-great-grandparents, only one of the four is a possible source of this X-match. Is that possible? Or should I be looking for another, as yet unidentified, connection between RBG and VRH?

  • #2
    More information is needed to determine what you are asking.

    For instance their path to both sets of grandparents is very important. Since they are both male they get their entire X from their mothers, their mother gets an x from her father and an x from her mother (you would not know which/combination they received at that point). So, you would have to keep going up from each man identifying their possible X contributors.

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    • #3
      That's what I did. Their possible X contributors intersect at one, and only one, person, one of their great-great-grandmothers. What I want to know is whether this is believable, given the size of the match, or if there is likely to be another link somewhere that I haven't found yet. I suppose I could post pedigree charts for their mothers, but I don't know if the color coding I use for possible X paths would show up very well.

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      • #4
        Originally posted by OldMtnLady View Post
        Based on what I’ve read about X inheritance patterns, of their four shared great-great-grandparents, only one of the four is a possible source of this X-match. Is that possible?
        Yes it is very possible for that much shared DNA to be coming from one ancestor.

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        • #5
          considering my grandpa shares 425 cm on gedmatch with one of his double third cousins, your uncle sharing that much x-dna with a third cousin isn't surprising

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          • #6
            Perhaps you have done this already or something similar, but I would look at Blaine Bettinger's X charts. To verify that your pathways are possible.

            Make sure you take only the male chart(s).

            http://thegeneticgenealogist.com/200...-x-chromosome/

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