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Using NON X-match strategy to Find MRCA

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  • #16
    My third sister to same Grandparents. All sisters are full siblings.

    All follow the X inheritance path to inherit XDNA from maternal Grandfather, but only 1 of the 3 did.
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    • #17
      Originally posted by ltd-jean-pull View Post
      I may not be understanding what you are trying to do.

      A distant male relative of mine shares no X-DNA with his maternal grandmother. He received his maternal grandfather's X-chromosome.

      Using your rationale if he wasn't an X-match to your mother you would be thinking he can't be related via any line that contributed X-DNA, whereas it is quite possible the connection is via his maternal grandmother.
      Can you explain further why you think it's quite possible? Thanks!

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      • #18
        Originally posted by John McCoy View Post
        Since it is indeed possible for a person to inherit a non-recombinant X chromosome from a female (and for a sibling to inherit the other homologous X chromosome!), the lack of X matches is not strong evidence for or against a particular relationship. Rather, the existence of an X match IS evidence of a relationship that follows the pattern of inheritance of the X chromosome.

        The lack of an X match may tip the odds, but I don't regard that as proof of anything.
        I know a lot of people have this same opinion, but if you use logic, pool A has Xmatches and therefore, the rest is pool B - nonXmatches. Thus, it follows that if you are not in pool A, you must be in pool B. So I think there is something here to investigate. Unless you can show us why it is not strong evidence? do you have an example?

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        • #19
          Originally posted by prairielad View Post
          My third sister to same Grandparents. All sisters are full siblings.

          All follow the X inheritance path to inherit XDNA from maternal Grandfather, but only 1 of the 3 did.
          I'm not sure I follow your logic. your sisters could inherit their x from either your maternal or paternal grandparents and they did... That follows exactly the x inheritance paths. So why would this disprove a nonXmatch?

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          • #20
            Originally posted by alphavisions View Post
            Can you explain further why you think it's quite possible? Thanks!
            Because it actually happened in the real life example that ltd-jean-pull presented. And it may happen in your case as well, which is why the assumption of no matching x segments may cause you to rule out a line in which the common ancestors actually may be found.

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            • #21
              Originally posted by alphavisions View Post
              I know a lot of people have this same opinion, but if you use logic, pool A has Xmatches and therefore, the rest is pool B - nonXmatches. Thus, it follows that if you are not in pool A, you must be in pool B. So I think there is something here to investigate. Unless you can show us why it is not strong evidence? do you have an example?
              prairielad and ltd-jean-pull gave you real-life examples.

              While a recombination of the two x chromosomes, one from her father and the other from her mother, is what a woman usually passes on to her children, there are known cases, not just for prairielad and ltd-jean-pull, where an unrecombined x from either the the maternal grandfather or grandmother is passed on whole to the child by his/her mother. You would not know this is the case in your situation unless you have tested the maternal grandparents and their grandchildren, as prairielad has done.

              So, he knows by mapping the x segments that the maternal grandfather did not contribute any xDNA to two out of three sibling grandchildren. You don't have that information until you do the same, which is why you can't safely assume what you're assuming in this thread.
              Last edited by MMaddi; 18th August 2017, 11:02 AM.

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              • #22
                As an example of X non-matching....

                My mother has a third cousin, so they share a gg gm, born in 1813. So we have detailed trees and plenty of census and other records.

                My mother shares 61 cM with her third, so very reasonable.
                My mother also shares a Matching mtDNA of GD = 0 with her third cousin. So a double DNA confirmation.

                The mtDNA path coincidentally follows an X path. Although they should share some X DNA, 12 cM, they don't. Not even 1 cM. Nada. Zero.

                So not all X cousins share X DNA.
                Last edited by mabrams; 28th August 2017, 06:40 PM.

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                • #23
                  Answer

                  While using gedmatch testing on 2 nonXmatches, they gave this information about non-Xmatching which I feel comfortable confirms there is some value to nonXMatches:

                  Based on X-DNA Genetic Distance, there is no relationship through the X-Chromosome. This means that the ancestry of one or both of these 2 individuals probably has one or more Father-to-son generations that has blocked the transfer of X-DNA. That eliminates possible relationship paths that do not contain father-son generations.

                  Feel free to use the information as you desire.

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