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  • Results interpretation question....

    I've received Y-37 results for a 4th cousin whom I've been encouraging to test. Our shared ancestor is our 3rd great grandfather, via direct paternal lines for both of us.
    I had expected an exact match, but instead we have a Genetic Distance of 1, due to a difference at DYS439 (12 for me, 13 for him).
    My questions are these:
    Do the location and numerical values of the mismatch have any relevance or significance? I gather that some locations are more important than other.
    Barring an NPE (highly unlikely in this case)what are probabilities of 4th cousins not being a full match at the 37 level?

    Thanks in advance for your help -- and patience. I'm new at this and have much to learn.

  • #2
    You might benefit from reading MMaddi's post today, #4 in this thread. He discusses the average years and generations possible for SNP changes.

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    • #3
      Originally posted by KATM View Post
      You might benefit from reading MMaddi's post today, #4 in this thread. He discusses the average years and generations possible for SNP changes.
      But MarkStickle is asking about STRs, not SNPs. STRs have a higher mutation rate and can relatively easily back mutate. So, what I wrote in the thread you linked to won't answer his specific questions.

      The basic answer to his questions is that STRs can only give a rough estimate of "time to most recent common ancestor" (TMRCA), based on average mutation rates. A 36/37 match with a 4th cousin is certainly very plausible, but you could also match 36/37 with a 5th or 6th or more distant cousin. If he wants a more reliable TMRCA, he and the 4th cousin should upgrade to 67 markers. That would as least give him a better estimate of TMRCA, but still no "slam dunk" answer.

      If he's trying to use DNA testing to confirm the paper trail to the common ancestor, it sounds to me as if he has. I suppose it's possible that the common ancestor may be one more generation back than he thinks (the common ancestor is the father of the ggg-grandfather and they're descended from different sons of the gggg-grandfather, making them 5th cousins), but I don't think STRs will give him enough resolution to say that either possibility is the case with certainty. DNA testing is based on averages and probabilities and can provide important clues, but ultimately has to be confirmed in the paper trail.
      Last edited by MMaddi; 29 January 2017, 01:49 PM.

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      • #4
        Oh dear, another senior moment!
        My apologies. Thank you for straightening it out.

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        • #5
          Originally posted by MarkStickle View Post
          I've received Y-37 results for a 4th cousin whom I've been encouraging to test. Our shared ancestor is our 3rd great grandfather, via direct paternal lines for both of us.
          I had expected an exact match, but instead we have a Genetic Distance of 1, due to a difference at DYS439 (12 for me, 13 for him).
          My questions are these:
          Do the location and numerical values of the mismatch have any relevance or significance? I gather that some locations are more important than other.
          Barring an NPE (highly unlikely in this case)what are probabilities of 4th cousins not being a full match at the 37 level?

          Thanks in advance for your help -- and patience. I'm new at this and have much to learn.
          Mark,

          Nothing to worry about. Brothers or father and son can be a genetic distance of one at 37 markers. In addition to that DYS439 is a fast mutating marker.
          Last edited by Jim Barrett; 30 January 2017, 05:08 AM.

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          • #6
            Follow up and thanks....

            This is very helpful and appreciated. In fact, my impression was that DYS-439 was relatively more prone to mutation than many others.

            I'm reasonably confident of the 4th cousin relationship from a shared 3rd great grandfather. Not only are the documentary trails well-established, but (more importantly, I think) the connection among lots of the 4th cousins and other descendents of the shared ancestor are supported by multiple autosomal tests. The "pieces of the puzzle" all fit together quite well. I think!

            Again, thanks to all. And if there are more insights or questions they'd be very welcome.

            MS

            PS. I've done the 67 marker test, and plan to upgrade the cousin in question sometime soon. As some of you may know, being the family genealogist has become a rather expensive business these days -- the number of tests I want to administer tends to run well ahead of my ability to fund them!!!!!

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