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What is significant for an X-Match

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  • What is significant for an X-Match

    How big does an X-Match between two females need to be before it is likely to be genuine?

    My mother has an 8cM X-Match with someone but on Gedmatch it isn't there at all.

    They also share a 30cM block on Chromosome 6. FtDNA and Gedmatch agree about this one.

    On FtDNA they have smaller matching blocks on four other chromosomes. On Gedmatch they don't. FtDNA predicts 3rd cousin, Gedmatch predicts 5th cousin.

    Is it worth pursuing the X-Match angle here?

    I'm suspecting not. Both relevant family trees are full of the same ancestral regions so the MRCA could be anywhere, on either or both sides of the tree. But I don't want to discount it if it might be important.

  • #2
    Actually, I've just noticed two kits on gedmatch in the same name, some contact email. The second kit is very similar to the FtDNA match. I'd say it is two different people tested, who are related.

    So only one question remains - How likely is an 8cM segment match on the X-Chromosome between two females to be IBD? I know the percentages for the rest of the autosomal chromosome but the X never seems to work for me. Seems the segments have to be bigger.

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    • #3
      Originally posted by larzus View Post
      Actually, I've just noticed two kits on gedmatch in the same name, some contact email. The second kit is very similar to the FtDNA match. I'd say it is two different people tested, who are related.

      So only one question remains - How likely is an 8cM segment match on the X-Chromosome between two females to be IBD? I know the percentages for the rest of the autosomal chromosome but the X never seems to work for me. Seems the segments have to be bigger.

      I am only seeing very small X-matches on FTDNA and they mean nothing. Not sure why FTDNA even shows these as a match.

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