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X-Match - Why are my paternal cousins x-matches?

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  • X-Match - Why are my paternal cousins x-matches?

    My paternal second cousins (descended from my father's paternal uncles) are all shown as x-matches to me (I am female) on their FTDNA test results. I understood that X-matches had to be descended either from my mother's line or from my paternal grandmother's line. Please explain why my paternal second cousins are x-matches.
    Liz

  • #2
    The first question is, how large are these X segments? Check them on the Chromosome Browser. If they are small, it is noise.

    X-DNA can't be passed down through two successive male generations. I gather from your name, Liz, that you are female; so you got one X chromosome from your father, and one from your mother. If the cousins are as you say, and descend from your father's paternal uncles (not your paternal uncles), then that is at least two male generations in a row, and no X is passed down. The cousins would be 1st cousins, once removed if they are children of your father's paternal uncles, and 2nd cousins if they are grandchildren of your father's paternal uncles.

    I suppose if there is any chance that your father's paternal uncles were related in some way to your paternal grandmother, you might share some segment on the X.
    Last edited by KATM; 31st January 2018, 09:31 AM.

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    • #3
      X-Match Chromosome Browser

      Thank you for your very clear response. Your description of the way in which X chromosomes are passed on is in line with my understanding. So I think the first sentence in your response i.e. 'how large are the X segments' is probably the solution.

      I do not fully understand how the Chromosome Browser works but looking at the data in tabular form for those eight second cousins who are x-matched to me, most of them are in the range 1.02 to 5.31 Cm with one cousin having an X segment of 15.12 Cm. Would you class these figures as low? If so why do FTDNA include such x-matches in the results if the figures are too low to be meaningful?
      Liz

      Comment


      • #4
        Originally posted by emk1950 View Post
        I do not fully understand how the Chromosome Browser works but looking at the data in tabular form for those eight second cousins who are x-matched to me, most of them are in the range 1.02 to 5.31 Cm with one cousin having an X segment of 15.12 Cm. Would you class these figures as low? If so why do FTDNA include such x-matches in the results if the figures are too low to be meaningful?
        Liz
        Your father’s paternal uncles (“great” uncles to you), as well as his paternal grandfather, each received their single X chromosome from their mother (your paternal great-grandmother). They would pass this X chromosome down to any daughters they might have. But your father received his X chromosome from his mother.

        If your mother, and your father’s mother, are not related to your father’s paternal grandmother, then the X chromosome matching you are seeing with these cousins is not inherited, but what is called “Identical by State (IBS)” or sometimes also called “Identical by Chance.”

        It would be good for you to fill out some X inheritance charts, just to make sure that there is no relationship between your mother, your father’s mother, and his paternal grandmother. You can find some at Blaine Bettinger’s blog “Unlocking the Genealogical Secrets of the X Chromosome.” (these are in “fan” chart format). Debbie Parker Wayne has some X-DNA inheritance charts in pedigree format. (also check her updated section for other versions, under “X-DNA” on that page).

        It's usually advised to consider a match first based on the autosomal DNA, and use the largest segment of that. Then, if the person is also an X match, the X chromosome can be used to narrow the field of probable contributing ancestors. For recent genealogical matching, if a segment on the X is less than 7 cM, or really even 10 or 20 cM, it may not be meaningful. So, most of the X matching with your 2nd cousins is likely just noise. I'm not sure about that 15.12 cM segment with the one 2nd cousin, though; best to check with X-inheritance charts to double-check that there is no other way you are related to that cousin.

        FTDNA includes very small matching segments for both autosomal and X-DNA in what they report. Basically, they are showing you everywhere you match, but this gives a misleadingly high count for total matching cM. Pay attention to matches with the largest segments.
        Last edited by KATM; 31st January 2018, 01:56 PM.

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        • #5
          emk1950, if you don't fully understand the Chromosome Browser, try these pages:
          • "Family Finder – Chromosome Browser Page" in the FTDNA Learning Center. There, they mention a Chromosome Browser Tutorial, but that doesn't appear to exist anymore; they should update wherever it's mentioned. The link for "Page Tour," on the Chromosome Browser page in your account, gives some minimal information, and then the "Learn More" link goes to the Learning Center page I linked to in this bullet.
          • Roberta Estes has a post about "Nine Autosomal Tools at Family Tree DNA," and the Chromosome Browser is discussed as tool #5 there

          Also: a benefit of having so many 2nd cousins tested is that the autosomal segments where they match you (and each other) are inherited from your common great-grandparents (paternal for you). This is good for mapping your chromosomes, to determine the common ancestor for your matches.

          You can use your 2nd cousins’ kits to filter some of your matches into a paternal list; see “Family Finder – Family Matching System” and "Family Finder Matching Tool” in the FTDNA Learning Center for instructions. You will need to either upload a GEDcom file to your "myFamilyTree" at FTDNA, or create one there.
          Last edited by KATM; 31st January 2018, 02:00 PM.

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          • #6
            Family Finder Table View

            Thank you so much for all this information which has been most helpful. I have looked at the tutorial you recommended which has thrown up a related question regarding the x-matches with paternal second cousins as described at the beginning of this thread. Looking at the Family Finder Table View, I see that some of my x-matches are shown as having anything up to 6 lines against the X chromosome. What does this mean? Do I add the figures together for all the X lines or just take the highest figure to decide whether the match is 'noise' or not?
            Liz

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            • #7
              I would disregard the lines showing segments below 5 cM, and see what's left. Perhaps you could post an image of one like this, though.

              Comment


              • #8
                At one point, about two years ago, I had 11 X matches to my father. I suppose there are more now.

                Of the 11, I found 3 of them on GedMatch, where I can do a better X analysis. X One to One, 1cM etc

                It turned out that on these three matches, I could find the exact same small X segments when matched to my mother. I have my mother's FTDNA test posted at GedMatch (my father is deceased).

                So while the autosomal matches were definitely paternal, it turns out the little tiny X segments were from my mother.

                (Both of my parents have similar Colonial ancestry and geography, although I have never found an actual common ancestor)

                Comment


                • #9
                  Xmatch - DNA analysis

                  In reponse to the reply from KATM of 2nd February, here is an example of a table with six X-matches. Apologies for the delay.

                  Comparison Data for: my 2nd Cousin
                  Chromosome Start Location End Location centiMorgans (cM) # of Matching SNPs
                  1 151090004 154525577 2.93 383
                  1 234684823 247093448 25.48 2423
                  2 53323314 58648028 3.77 668
                  2 100691380 223858027 112.36 15073
                  3 19451449 21466429 1.87 277
                  3 61982076 63105909 2.13 277
                  3 119805606 122056825 1.88 321
                  3 128892631 131687123 2.06 307
                  3 132224377 134373367 2.18 292
                  4 55724591 83887434 24.93 3045
                  4 102455937 105185034 1.92 255
                  5 8468608 55295078 45.87 5645
                  10 9438571 10816149 2.47 254
                  13 54327965 58723000 2.04 296
                  15 80231492 83889346 3.04 282
                  20 16744590 59813113 63.39 7057
                  X 1370495 4827433 15.12 275
                  X 71991396 80020571 1.01 470
                  X 103383448 107870033 1.25 343
                  X 135558221 137934767 1.99 284
                  X 143211353 145480429 5.07 407
                  X 151913936 154570039 5.31 377

                  Liz

                  Comment


                  • #10
                    (I amended your post to add some dots for the figures, and shortened the column headings, to make the alignment easier to view)
                    Originally posted by emk1950 View Post
                    In reponse to the reply from KATM of 2nd February, here is an example of a table with six X-matches. Apologies for the delay.

                    Comparison Data for: my 2nd Cousin
                    Chr. . .Start. . . . . . . . . . .End. . . . . . . . .cM. . . .#SNPs

                    X. . . . . 1370495. . . . .4827433. . . . .15.12. . .275
                    X. . . . 71991396. . . . 80020571. . . . . 1.01. . .470
                    X. . .103383448. . . 107870033. . . . . 1.25. . .343
                    X. . . 135558221. . . 137934767. . . . . 1.99. . .284
                    X. . . .143211353. . .145480429. . . . . 5.07. . .407
                    X. . . .151913936. . .154570039. . . . . 5.31. . .377

                    Liz
                    The amount shared on chromosomes 1-22 (1-20 in this case) equaled something close to 272 cM, when counting only the segments about 5 cM. This is, as your known relationship shows, an amount that includes 2nd cousins. So we are good with that part.

                    I quoted just the X chromosome amounts above. Really the only one that you should count is the first line, the segment from 1370495-4827433, for 15.12 cMs and 275 SNPs. The SNP amount might be on the weak side, but since the segment is 15 cM, it is large enough to not be "noise" on the X chromosome. I was just reading something yesterday which said that segments on the X should be halved to be consistent with segments on the other chromosomes (1-22). If that is true, this 15 cM segment should be looked upon more as how a 7.5 cM segment on the other chromosomes would be. And that is: about the lowest range to be considered worthwhile. It may still be false, or IBS.

                    If this is a paternal second cousin, your common ancestors are your great grandparents, paternal on your side.
                    From my earlier post:
                    If your mother, and your father’s mother, are not related to your father’s paternal grandmother, then the X chromosome matching you are seeing with these cousins is not inherited, but what is called “Identical by State (IBS)” or sometimes also called “Identical by Chance.”
                    Have you eliminated any chance that such a relationship exists between the relatives above?
                    Last edited by KATM; 9th February 2018, 08:38 PM.

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                    • #11
                      The X analysis here is focusing on paternal lines and ignoring the other obvious possibilities.

                      Either your paternal uncles married women related to your mother or their children's spouses are related to your mother.

                      You may not be able to determine the relationship to your mother. Small amounts of matching X DNA can be from 10 to 20 generations ago.

                      Comment


                      • #12
                        Conclusion

                        Thank you KATM, your responses have been both helpful and interesting and I now feel that I have at least some understanding of the X chromosome.

                        However, I would like to confirm that I have researched both my maternal and paternal lines extensively (5 generations or more) and can find no possibility of a relationship between my mother, my father's mother and my father's paternal grandmother. If there is a link at all it will be too far back to be of use. I am now more inclined to think that the X-matches as described in previous posts are 'noise' or false positives.


                        Thank you again.
                        Liz

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