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No X match between brother & sister

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  • No X match between brother & sister

    I uploaded my brother's raw data to GEDmatch and compared the X chromosome. To my shock 0.0 cM match, even when lowering the cM threshold to 3.5. Does this mean my X comes mostly from my father's mother? Is this unusual?

  • #2
    Nevermind. GEDmatch shows no X match segments but FTDNA results show us as x matches. Just got list of matches seconds ago.


    • #3
      Females have 2 X's (one from father, one from mother), males only have 1 X (one from mother)

      The X you received from your father, will be from his mother. Your other X will either be your mother full paternal X, her full maternal X, or a random recombination of her paternal and maternal X's

      Your brothers X will be either be your mother full paternal X, her full maternal X, or a random recombination of her paternal and maternal X's

      That said two full siblings could possibly receive the opposite X's from mother and end up not matching on X (Rare)

      I would first confirm if you have uploaded the X chromosome Raw Data for each kit correctly and possibly wait a bit longer for Gedmatch to process kits.

      If both kits have tested at FTDNA check the chromosome browsers X chromosome when comparing both kits.

      Another thing you can check is to run raw data through David Pikes Utility and see if it comes up with a match. Build number has to be the same to run utility (either both have to be build 36 or both have to be Build 37)
      Also before running, open FTDNA's X raw Data file and confirm whether if it is sorted from smallest to largest based on the numbers in the Position column.
      If it is sorted by RSID number it will not work with utility.
      File will have to be modified to work with David Pikes utilities.


      • #4

        I think I need to give FTDNA a day or so to finish processing my brother's test. My raw data was transferred from AncestryDNA months ago to FTDNA. It had already been uploaded to GEDmatch. I uploaded my brother's just hours ago after you told me which build to use. :-) At that time FTDNA didn't have any matches showing for my brother. Now, I'm showing up in his matches as an X match, but I'm not able to use the chromosome browser with him. On GEDmatch, while it indicated no matching segments on the X I could see some yellow lines, just nothing significant. Would the fact our DNA was processed by the two different companies have any bearing on the results for the X?


        • #5
          It could, it just depends on which snps (rsid number)each company tested.

          You would have to open your x raw data file from ftdna and see if a high number of no calls are shown (-- equals no call)

          any snp that ftdna tests that is not tested by ancestry will show up in transfers raw data at ftdna as a no call. In turn, any ancestry's tested SNP's that ftdna does not test will be omitted from ftdna raw data file..

          but I think ancestry and ftdna use the same testing chip


          • #6

            I looked at my brother's raw data for the X chromosome.

            1. The "position" is the sort feature, not RSid.

            2. The "no call" rate seems in the 6% range, based on there being 40 no calls in the first 631 RSids. That's as far as I counted. :-)

            I will run them through GEDmatch again tomorrow and look closer at the results before trying the other utility you mentioned. I'm also hoping FTDNA completes processing his FF test and I'm able to use the Chromosome Browser.

            Thanks for your help today.


            • #7
              Much different results this morning at GEDmatch.

              Largest segment = 75.6 cM
              Total of segments > 7 cM = 112.2 cM Actual.



              • #8
                I inherited my maternal grandmother's X unrecombined, I haven't tested my brother yet but it's possible he could have inherited my maternal grandfather's X unrecombined....then we wouldn't have any X chromosome in common.
                The inheritance pattern of the X really fascinates me. I was able to trace at least 22cm of my X to my 6th great grandparents.