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Small X match valid?

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  • Small X match valid?

    In Family Finder I match a brother & sister whose surname is the same as my great-great-grandmother. This surname is the only common connection we can find in our family trees-- and the location & history would be right for a match in this lineage.

    On GEDmatch, I see that the sister and I share an X-match at 4.1 cM (I am male). When I looked at the X-DNA inheritance for males, my great-great-grandmother is not within the frame of inheritance. Does this prove that we could not be related from the family we believe we share? Is it possible that 4.1 cM could be a false result? Could the X-match with the sister be from a different relation we don't know about yet?

  • #2
    If there is no autosomal match, I would not invest much time in a small (say, less than 10 cM) matching segment on the X chromosome. The relationship is probably very distant, and likely too far back to be provable.

    It is worth remembering that around 10% of actual third cousins are not found as autosomal matches (where the criteria for a match include at least a 10 cM autosomal segment or some similar measure), and possibly as many as 50% of real 4th cousins don't match. One way of looking at these statistics is that the absence of a match does not prove the absence of a relationship 4 or more generations back. It is best to concentrate first on the closer predicted relationships, where the probability of finding something useful is much higher.


    • #3
      We do have an atDNA match. With the brother I share 11.2 cM 1,658 SNP and with the sister I share 11.2 cM 2,135 SNP (plus the X match). Our MRCA is estimated to be 5.2 generations back.


      • #4
        It could be that the x match is a small segment that has travelled down through a completely different ancestor as sometimes x segments can survive for many many generations. So for that reason ignore it in this case, it doesn't negate the match you are working on.