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What exactly does an X-match mean, and what are the rules?

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  • What exactly does an X-match mean, and what are the rules?

    My mother's paternal uncle is an X-match to her: what exactly does this mean?

  • #2
    Two things to watch for: First, be sure that the matching segment on the X chromosome is long enough to be "real" -- 10 cM at a minimum, and if you happen to find an X match on GEDmatch's One-to-Many report, be sure to VERIFY it by using the X One-to-One comparison tool. Second, understand how the X chromosome is inherited: Males get one (possibly recombined) X chromosome from their mother, none from their father. Females get one (possibly recombined) X chromosome from their mother, and one intact, not recombined X chromosome from their father. There are many, many charts on the internet showing this pattern of inheritance.

    In your situation, your mother inherited one intact X chromosome from her father, who got that X chromosome from his mother. The uncle (your mother's father's brother) also got all or part of that same X chromosome from his (their) mother, which is as it should be.

    X matches are of interest for genealogy mainly when they show that two people MUST be related through the chain of inheritance of the X chromosome. Absence of an X match is often not informative, though that's another story! The presence of an X match for two people who don't show a reasonably strong autosomal match is problematic: unless you have some idea how two people are related, an X match is almost impossible to interpret, even if it is so large that it has to be real.

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    • #3
      http://www.genie1.com.au/blog/63-x-dna

      Rhonda, this link shows one example of the patterns of inheritance on the X for each male and female.

      This is also another chart which I like better, but cannot find at the moment. It is more like a fan chart.
      Last edited by Biblioteque; 9th November 2018, 07:04 PM.

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      • #4
        This is my first posting. I'm hoping to solve a dead end on my maternal side. My mothers paternal great grandmother is listed in census records by her husbands surname but he is not listed perhaps killed in the Civil War.I'm trying to find her maiden name and have taken Family Finder. My closest X matches are at 70 cm and longest block of 24 with 48 individual matches with the least being 30 cm at 15 block. Can I find what I'm looking for using this info.
        Last edited by Raven45; 12th November 2018, 05:48 PM.

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        • #5
          Raven45, have you researched any Civil War records to see if you can confirm your hypothesis and possibly get leads for finding genealogical data?

          What parameters were you using on you X-DNA 'one-to-one' comparisons? I am assuming that you were doing that on GEDmatch.

          I find X-DNA comparisons virtually worthless when you are looking at common ancestors more than a few generations back.

          Jack
          Last edited by georgian1950; 12th November 2018, 07:01 PM.

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          • #6
            Originally posted by Raven45 View Post
            This is my first posting. I'm hoping to solve a dead end on my maternal side. My mothers paternal great grandmother is listed in census records by her husbands surname but he is not listed perhaps killed in the Civil War.I'm trying to find her maiden name and have taken Family Finder. My closest X matches are at 70 cm and longest block of 24 with 48 individual matches with the least being 30 cm at 15 block. Can I find what I'm looking for using this info.
            I think most of us can feel your pain to varying degrees on trying to research any maternal branch of our family trees going back to before 1850 in the United States, the quality, and condition, of the records available from that time frame leaves a lot to be desired.

            Now as to what I understand to be the case with the X-DNA matches on your Mother's Paternal Great-Grandmother, we'd need clarity on which "line" we're running down. If we're talking about the Patrilineal Line(the one that can be tested with Y-DNA), you're pretty much sunk before you start.

            To try to generate a mini table:
            1st entry is mother's father, 2nd is mother's grandparent, 3rd is mother's great-grandmother

            M-M-F (No X-DNA match possible through this line directly)
            M-F-F (X-DNAmatch possible, mtDNA testing of a cousin on a F-F-F branch of that line may be advised if possible. But the utility of such a test is limited, speaking from first-hand experience on that front)

            Basically the thing that helps on X-DNA, particularly on male lines, is that when it runs through a Male Generation, recombination is greatly curtailed, so it allows a little bit of extra reach. With "maximum effect" being found on a line that runs M-F-M-F-M-F from generation to generation. The one thing that will stop it cold however, is successive M-M generations, as male fathers cannot pass on their 23rd X Chromosome to their sons. What makes X-DNA hard to work with is trying to find the paper trail to support such a M-F-M-F-M-F progression as maternal lines tend to be very poorly documented in a lot of places as you proceed further back into the 19th century. This is also the major problem for mtDNA as well.

            X-DNA sees further complications from incest, endogamy, and the whole matter of "multilple choice" as to how or where that DNA may have come from. "Greedy matching" on the part of alogorythms which have no way of knowing which parent contributed which segment of DNA for either matched person further compounds things. This is where testing multiple people, on both sides, potentially helps rule out a match by chance vs match by descent. But that likely only works after contending with the additional frustrating part of 23rd chromosome inheritance specifically.

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            • #7
              Bartarl260, you are right and it appears that I can't get the answer I'm looking for using Family Finder X. The line of descent is indeed mother, her father, his father and lastly his mother. This certainly also explains why I am getting matches to surnames that were unknown or distant cousins on the periphery of my family tree.

              Georgian1950, yes I have searched the Civil war as well as marriage records of the county they lived in but haven't uncovered anything definitive yet.

              Thank you both for taking the time to help me with my search.

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              • #8
                At least for a Civil War soldier on the Union side who left a widow, the widow (under her married name) should be listed in the US Civil War pension index. Her application for a pension as the widow of a Union soldier should document her marriage. Don't forget to track down US Census mortality schedules as well as STATE (not Federal) census records. If you happen to be researching in Iowa, for example, what you need might be in one of the state censuses.

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                • #9
                  Thanks John McCoy, the ancestor in question was a Confederate soldier. I will check the records available and see if anything turns up.

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                  • #10
                    One thing nobody ever seems to mention is the fact 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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                    • #11
                      Originally posted by snetphilie View Post
                      One thing nobody ever seems to mention is the fact 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
                      Thank you, that's both amazing and creepily confusing: DNA is like Puck playing pranks and even genealogists are always getting fooled!

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