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X-matches on FTDNA

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  • X-matches on FTDNA

    I'm so confused about X-matches.

    I have 51 X-matches on FTDNA. Is it safe to assume that all 51 of those matches are on my mothers side? And not my fathers?

    There are 2 sister's that are on my X-match list, that I've been very interested in. I've been thinking that they are somehow tied to my dad's birth mother, but now I'm not sure. If they are indeed on my mom's side, I've wasted a lot of time/research trying to match them to my dad.

    I match both sisters the same spot on Chrom X, for 2.7cM.

    Beyond Chrom X, I also match on 18 segments, and they are predicted to be 2nd - 4th cousins.

    ** I'm not adopted, but my dad is. (passed away) I've been trying to find his birth-parents for almost a year now.

    ** Fishing in all ponds, plus Y-67.

    Greatly appreciate any clarification on this.

  • #2
    No, it's not safe to assume that all X-matches are from your mother's side. Also 2.7cM is not a large enough piece of shared DNA to be useful.

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    • #3
      X matching is an aid, but not fool proof

      It is recommended on X that anything under 10cM will have a high chance of being a false X match. Many people say only focus on X if segment is over 20cM.

      Male to Male X comparison have a higher chance of segments being true. Each only has one X value to compare.

      Male to Female X comparison will cause a higher number of false X segments over a Male to Male comparison.
      Males one X value compared to females two. Only one of females has to match males single value to form a single value sequence, which can cause a false segment on smaller segments.

      Female to Female X comparison will cause the highest number of False X segments. Comparing both females 2 values against one another to form a single value sequence.

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      • #4
        Plus it's very important to remember that part of the X chromosome recombines with the Y Chromosome.

        So it is in fact possible for you to inherit part of your X chromosome from your mother's father's father. Your mother's father's X partially recombined with his Y, so one of your mother's X's contains a portion of her father's Y, and then her two X's recombine and you likely get some of that passed onto you.

        The same holds true for your father. Part of his X and Y recombined, so if you are male, you received part of the X he got from his mother in your Y chromosome, and of course the rest of the Y from him, but even his Y was a combination of his father's X and Y. If you are female, you still receive part of the Y that your father got from his father.

        Moral of the story is, the X match doesn't filter out the part of the X that recombines with the Y, so it is not a very accurate indicator of anything.

        Oh, and here's a video that shows how the X/Y recombination is different than the other chromosomes! https://www.biointeractive.org/class...n-y-chromosome

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