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"x-match" means that the connection is coming from your mother?

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  • "x-match" means that the connection is coming from your mother?

    I'm a man, and I would like to understand better my "x-matches". I suppose they are coming from my mother. Or not?

    Thank you a lot for helping so much in this forum!

  • #2
    Since you are male, yes, your X-matches will be from certain ancestors in your mother's side of your tree, but not all of her ancestors. Your father gave you your Y-chromosome, but no X-chromosome, so none of his ancestors contributed to your X.

    I made a post a long time ago, with more links about the X chromosome than you could shake a stick at (well, figuratively speaking, at least). Try the two under "Learn about the X-Chromosome," and some of the charts in that post, to help you visualize the ancestors who could contribute to your X-chromosome.

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    • #3
      I was asking because from my father side I've got a couple of "x-matches" and it is difficult to understand why.

      Thank you for your very helpful post!



      Originally posted by KATM View Post
      Since you are male, yes, your X-matches will be from certain ancestors in your mother's side of your tree, but not all of her ancestors. Your father gave you your Y-chromosome, but no X-chromosome, so none of his ancestors contributed to your X.

      I made a post a long time ago, with more links about the X chromosome than you could shake a stick at (well, figuratively speaking, at least). Try the two under "Learn about the X-Chromosome," and some of the charts in that post, to help you visualize the ancestors who could contribute to your X-chromosome.

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      • #4
        FTDNA will declare an X match for all segments down to 1cM/500SNP.
        Majority of segments under 7cM tend to be false positive.

        Are the X segments for these paternal matches under 7cM?

        You can get segments sizes by viewing match in chromosome browser and clicking on View in table

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        • #5
          False positive for X match

          Originally posted by prairielad View Post
          FTDNA will declare an X match for all segments down to 1cM/500SNP.
          Majority of segments under 7cM tend to be false positive.

          Are the X segments for these paternal matches under 7cM?

          You can get segments sizes by viewing match in chromosome browser and clicking on View in table
          That answered my question I came here to get help with! I'm lucky that I unlocked chromosome browsing on the person whose DNA I'm researching. Should FTDNA not give a little disclaimer about this on the Family Finder - Matches page?!

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          • #6
            I agree! FTDNA and other vendors could do a much better job of putting some plain-language context around the results. A novice who is dumped into genetic genealogy will lack context, which, in this subject, is extremely important. It would help immensely if we could all go back in time and pay attention in high school or college biology during the unit on meiosis.

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            • #7
              Does anyone know if ftdna report 48xxxy syndrome to the customer?

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              • #8
                Originally posted by prairielad View Post
                FTDNA will declare an X match for all segments down to 1cM/500SNP.
                Majority of segments under 7cM tend to be false positive.
                This is something that everyone has wrong.

                When I was weighing how low you can go on your parameters, I came up with this idea. For a given set of parameters, say x SNP's and y minimum segment size in cM's, if you can find any two kits that do not match, the chances that those parameters would cause any false positives in comparing any two kits is practically nil. Those parameters are just not spewing forth false matches stochastically.

                So, why do we have all of the matching segments which defy explanation? They come from the parents sharing a common ancestor and the DNA from both comes together to reconstruct a segment of that common ancestor's DNA.

                Given the nature of males not passing a X-chromosome to a son, I can find pairs of kits that do not produce any matching segments using parameters as low as 100 SNP's and 1.0 cM minimum segment.

                As for showing a matching X segment believed to be on a male's father's side, it comes from the mother having a common ancestor on the father's side, possibly even being a reconstructed segment from DNA of both of her parents.

                Basically X-DNA matches are not worth the time of day (even though they are not false-positive), except for cases within just the first few generations (where total amount of match may give a clue to the nature of the relationship). Spending your time on the other 22 chromosomes is a better use of time and effort.

                Jack Wyatt
                Last edited by georgian1950; 29 April 2018, 06:09 AM. Reason: clarity

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                • #9
                  Here are the details on my case re false positive for X match:

                  My FIL has two very good matches on each side. GEDmatch tells me that my FIL's parents were not related to each other.

                  His paternal side match is a half great-niece, confirmed also through family tree research, with 322 cM in common.

                  His maternal side match is also a half great-niece, also confirmed through family tree research, with 447 cM in common.

                  No problems here. But then comes a match, an unknown female person with 143 cM in common. This person shows as an X match and a "match in common" with the niece on the father's side, and I know this X match cannot be valid. So I check the chromosome browser and the X match doesn't show until I move the option down to 1 plus cM.

                  I was actually ok at biology and I remember meiosis. I just don't see what the utility is for making "X match" its own column on the Family Finder Matches page if it will be false a great deal of the time. Thanks!

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                  • #10
                    Originally posted by prairielad View Post
                    FTDNA will declare an X match for all segments down to 1cM/500SNP.
                    Majority of segments under 7cM tend to be false positive.

                    Are the X segments for these paternal matches under 7cM?

                    You can get segments sizes by viewing match in chromosome browser and clicking on View in table
                    A male can't get falsely large X matches though as there is no opposite strand to provide a fill in.
                    It probably means that you are related to the person on both sides of your family, possibly much farther back on your mom's side.
                    I just got a big 21cM match in common with my dad that is also marked as 4cM on X for me and only 1cM on X and in a different spot for my dad. My mom has no match. Probably it's a closer match on my dad's side and potentially a quite distant match on my mom's side.

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                    • #11
                      Originally posted by Susanna View Post
                      Here are the details on my case re false positive for X match:

                      My FIL has two very good matches on each side. GEDmatch tells me that my FIL's parents were not related to each other.
                      the fact it says they are not related doesn't mean anything solid

                      1. you can still end up having parents share matches even if they are not related in any way at all

                      2. also, due to random inheritance, they can be tree related in a reasonably close time span and yet not share any DNA in common but still share DNA in common with the same matches, just different parts

                      my parents get 0% related on GEDMATCH and don't match each other on any site and yet I share LOTS of matches in common with each

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                      • #12
                        That could be that the person in question is related to both of your parents by some means, not that your parents are related to each other. Just because you have a 3rd cousin on your mother's side married to a 4th cousin on your father's side doesn't mean they were closer than 5th cousins prior to the marriage.

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                        • #13
                          Originally posted by wombat View Post

                          A male can't get falsely large X matches though as there is no opposite strand to provide a fill in.
                          It probably means that you are related to the person on both sides of your family, possibly much farther back on your mom's side.
                          I just got a big 21cM match in common with my dad that is also marked as 4cM on X for me and only 1cM on X and in a different spot for my dad. My mom has no match. Probably it's a closer match on my dad's side and potentially a quite distant match on my mom's side.
                          No X match over 7cM is likely to be false positive, but even for males, smaller segments can be false positive, especially if comparing to a female.
                          Algorithm is matching males single value to females two values. Only one of females has to match to create a matching segment and If it is finding a small segment by zig zagging back and forth between females maternal and paternal X values it will be creating a false matching segment.

                          Not all smaller then 7cM segments are false, but maybe to far back to trace, thus one maybe focusing on the wrong set of ancestors to find common ancestor.

                          It is recommended to use X as an aid if there is a longest segment of 10cM or greater (some recommend longest segment of 20cM), This is not total cM shared on X, but longest segment.

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                          • #14
                            Also highly recommended, if using GEDmatch, ALWAYS verify the X match using the X One-to-One comparison tool!

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                            • #15
                              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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