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Private SNPs Matching and STR Conflict

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  • Private SNPs Matching and STR Conflict

    On Y-67 I do have a match at GD=1 which would indicate a common ancestor at 16 to 20 generations at 95-99 % certainty.
    The age of my subclade (R-FGC14600) calculated from three BigY's by YFULL is about 600 years. I do have five private SNPs. My match tested those five at YSEQ and ALL came negative. Does this make any sense?

  • #2
    Yes, it makes sense. Your private SNPs would only be shared with someone much closer in a genealogical time frame and would then no longer be private. The common ancestor percentage is an estimate and only based on the averages of others. This match could easily still be part of that 1-5% that shares your common ancestor past those 20 generations.

    If your match were to take a Big Y, maybe you find your common ancestor was from 700 years ago. Or those 5 private SNPs of yours are from 400 years ago and your match is from a different branch from 500 years ago. No way of knowing before your match takes it.

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    • #3
      I assumed it would match at least some SNP based on the supposed mutation rate which is every, say, 140 years (hence 700 years would be included)... But of course, the 600 years YFULL estimate could be optimistic or...

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      • #4
        The mutation rate is also based on an average. Some can happen sooner while others later.

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        • #5
          Originally posted by goldschlager View Post
          On Y-67 I do have a match at GD=1 which would indicate a common ancestor at 16 to 20 generations at 95-99 % certainty.
          The age of my subclade (R-FGC14600) calculated from three BigY's by YFULL is about 600 years. I do have five private SNPs. My match tested those five at YSEQ and ALL came negative. Does this make any sense?
          95-99 % certainty
          That leaves 1-5% cases when GD=1 with Y-DNA67 test does not indicate a common ancestor within 16-20 generations.

          Mr W

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          • #6
            Originally posted by goldschlager View Post
            The age of my subclade (R-FGC14600) calculated from three BigY's by YFULL is about 600 years. I do have five private SNPs. My match tested those five at YSEQ and ALL came negative. Does this make any sense?
            Did your match test FGC14600 itself?

            Has YFull already measured your Y-STRs from your BAM file--and have you verified that these match your regular FTDNA results?

            I ask because in my project, an apparent sample switch occurred recently. We eventually persuaded FTDNA to re-run the Big Y on a new sample.

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            • #7
              Originally posted by lgmayka View Post
              I ask because in my project, an apparent sample switch occurred recently. We eventually persuaded FTDNA to re-run the Big Y on a new sample.
              How was it detected? Were the STR markers from a Y-STR test compared with the ones from a Big Y, or was it through a different method?

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              • #8
                Originally posted by The_Contemplator View Post
                How was it detected? Were the STR markers from a Y-STR test compared with the ones from a Big Y, or was it through a different method?
                1) A very close Y-STR match with the same ancestral surname ordered a SNP pack, and got very different results from the first person's Big Y.

                2) YFull measured the Y-STRs of the first person's Big Y. Those Y-STRs did not come close to matching FTDNA's original set.

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                • #9
                  Yikes, hopefully the tester of the Big Y of whoever they switched with also got their corrected results.

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