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Gedmatch and the X

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  • Gedmatch and the X

    A friend of mine and her daughter (they've tested with 23&me and FTDNA) have a query. They are both matched with another party autosomally (the mother has 40.5cM and the daughter 38.8cM affinity totals), but only the daughter is related on the X (she has a common chunk of 11.8cM with the third party, while the mother has ZERO). Is this a Gedmatch glitch or does it have an explanation? There is afaik no paper trail relationship with that third party.

  • #2
    The daughter (XX) could match on the basis of the paternal X. This would indicate that the daughter is related to the match through both her parental lines.

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    • #3
      That makes sense. Thanks. I'll tell them.

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      • #4
        I agree, the difference is likely the X chromosome the daughter inherited from her father.

        Also verify that the mother matches the daughter on the X chromosome. If not, it is likely that the mother's X chromosome data was not uploaded to Gedmatch. (FTDNA, unlike 23andMe, separates the X chromosome data into another data file)

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        • #5
          Hi

          Wondering why do I share small X-chr. segments with 95% of my distant matches in my Gedmatch list,but only with very few of my closest matches?

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          • #6
            Originally posted by Carolus View Post
            ... why do I share small X-chr. segments with 95% of my distant matches in my Gedmatch list,but only with very few of my closest matches?
            Are you male or female?
            How big are the small segments shared with most distant cousins?
            What, if any, are the shared characteristics of your closest matches?

            Generally, such results indicate you are broadly and distantly related to a population based on shared ethnicity/ancestry but you have none or few close matches based on the same ethnicity/ancestry.

            If you are male all X-based cousins are through your maternal lines. If you are female some X-based cousins are through your maternal lines and some through your paternal lines. If male your X matches are closer. If female the matches through your maternal X are closer and those through the paternal line more distant due to the generational retardation of X recombination in paternal X.

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            • #7
              X inheritance question

              Originally posted by tomcat View Post
              Are you male or female?
              How big are the small segments shared with most distant cousins?
              What, if any, are the shared characteristics of your closest matches?

              Generally, such results indicate you are broadly and distantly related to a population based on shared ethnicity/ancestry but you have none or few close matches based on the same ethnicity/ancestry.

              If you are male all X-based cousins are through your maternal lines. If you are female some X-based cousins are through your maternal lines and some through your paternal lines. If male your X matches are closer. If female the matches through your maternal X are closer and those through the paternal line more distant due to the generational retardation of X recombination in paternal X.
              This is my problem : I am looking for relatives of my maternal gmother. I have taken Mtdna, FF+ FGS. I have no older relatives to test . Someone suggested
              I have my brother take the x chromosome test at 23 & me, but how would that help? My mother's parents ancestry was british isles for both her mother and father. So it seems to me that i would still have difficulty determining which matches came from my paternal gfather and which were from my maternal gmother.

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              • #8
                Originally posted by SCnMD View Post
                This is my problem : I am looking for relatives of my maternal gmother. I have taken Mtdna, FF+ FGS. I have no older relatives to test . Someone suggested
                I have my brother take the x chromosome test at 23 & me, but how would that help? My mother's parents ancestry was british isles for both her mother and father. So it seems to me that i would still have difficulty determining which matches came from my paternal gfather and which were from my maternal gmother.
                If your brother took the 23&Me test, that includes coverage of the X chromosome, you would know that his single X came from your mother and that it was a recombined product of the two X's she got, one from each parent - your maternal grandparents.

                You would still have the problem of sorting the maternal grandfather's contribution from that of the maternal grandmother and that would not be facilitated by the fact that both maternal grandparents were both of British Isles ancestry unless one was of a distinctive sub-population like Welsh, Irish, Cornish, Scots etc. and you knew which maternal grandparent belonged to such sub-population.

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                • #9
                  Originally posted by tomcat View Post
                  If your brother took the 23&Me test, that includes coverage of the X chromosome, you would know that his single X came from your mother and that it was a recombined product of the two X's she got, one from each parent - your maternal grandparents.

                  You would still have the problem of sorting the maternal grandfather's contribution from that of the maternal grandmother and that would not be facilitated by the fact that both maternal grandparents were both of British Isles ancestry unless one was of a distinctive sub-population like Welsh, Irish, Cornish, Scots etc. and you knew which maternal grandparent belonged to such sub-population.

                  Thanks, thats what I thought

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                  • #10
                    Originally posted by tomcat View Post
                    Are you male or female?
                    How big are the small segments shared with most distant cousins?
                    What, if any, are the shared characteristics of your closest matches?

                    Generally, such results indicate you are broadly and distantly related to a population based on shared ethnicity/ancestry but you have none or few close matches based on the same ethnicity/ancestry.

                    If you are male all X-based cousins are through your maternal lines. If you are female some X-based cousins are through your maternal lines and some through your paternal lines. If male your X matches are closer. If female the matches through your maternal X are closer and those through the paternal line more distant due to the generational retardation of X recombination in paternal X.
                    Hi Tomcat,
                    Sorry,I didnĀ“t mention that I am a male and my ancestry is total Finnish.
                    My shared segments are very small only 3-4 cMs and distant.I have many close matches,but I do not share X-segments with many of them cause of my only maternal X. However,Finland is a genetic isolation and I would not expect to see so many zeroes with other Finns. It is said that the diversity of X-chromosome is much lower than in autosomes.In addition,less number of recombinations.
                    I am still wondering why I have not more zero X segments shared with my distant autosomal matches,most foreigners.

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