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  • X Match ??

    I'm not the most knowledgeable when it comes to genetic genealogy so please excuse me if I'm missing the obvious. My Dad tested on Ancestry and I uploaded the results to both FTDNA and Gedmatch. We have the same match in common in all 3. FTDNA say X-match in the results. Gedmatch says there is no X-match. If it was an X-match, it is going to change the direction of my research. How do I know which is correct?
    Last edited by Rahnee; 26th December 2017, 06:03 PM.

  • #2
    How long is the shared segment on the X chromosome at FTDNA? If it's under 7 cM definitely ignore it and you may be able to ignore it if it's under 10 cM. FTDNA confuses a lot of people by calling matches X matches when the shared segments are so tiny they are probably just segments that occur in the general population. I don't know why they do that.

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    • #3
      One thing nobody ever seems to mention is the fact that part of the X chromosome recombines with the Y Chromosome. I know for sure that as of the time I am writing this, FTDNA does not differentiate between the part that recombines and the part that doesn't (I know... it sucks). If gedmatch is saying that there isn't an x-match, I'm guessing they are dismissing the part that recombines which obviously gives you much more useful information, because it limits the number of people you could have inherited it from.

      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.

      If you only look at the part that doesn't recombine, for men, they get that part from their mother, who got it from both her parents, but her father only got it from his mother. So only 3 of the 4 great-grandparents on that side contributed. For women it's the same, except it's both sides of her family, so for her it's 6 out of 8 grand-parents she got it from.

      Moral of the story is, the FTDNA 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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