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X Match

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  • X Match

    I have a known match with my first cousin. She is from the maternal side of the family, my mother's sisters child. I am male and we have in addition an X match.

    I am under the impression that a male gets his X Dna from his mother. Therefore when I match with other X matches, say a third cousin you would assume that this third cousin X match would also match my first cousin. However when I do an In Common Match they do not in most cases show .

    So I must have an incorrect grasp on this

    I am sure someone will be able to help me with this


  • #2
    Your mother(and cousins mother) has two X chromosomes, one from their father (which is identical in both sisters if full siblings), and one from their mother (random recombination of their mothers 2 X's).

    You received a random 50% of Your mothers two X's to form your single X

    Cousin received a random 50% of her mothers two X's to form one of her X's, her other X came from her father.

    Where you match your cousin you will be matching on shared segments of your maternal Grandfather(his mother) and/or maternal Grandmother

    Any X matches you have, to be shared with your cousin they would have to overlap a segment you share with your cousin.

    X matching at FTDNA is also only shown if that match shares an autosomal segment. FTDNA does not match on X alone no matter what size of segment there is if there is no autosomal match.

    As well any segment under 7cM is likely to be a false positive (IBS - Identical by state)
    Last edited by prairielad; 26 May 2017, 10:13 AM.


    • #3
      X Match

      Thank you for this explanation. I got it now.