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GD of 6 @ 67 STR for 2nd Cousins Once Removed

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  • GD of 6 @ 67 STR for 2nd Cousins Once Removed

    Just got results back for a 67-STR y-DNA test that showed a genetic distance of 6 between the donor and an individual who is a known second cousin, once removed.

    One individual is 3 generations from the MRCA and the other is 4 generations out, each a descendant of sons of MRCA.

    This seems way out of bounds for y-DNA results for two men that close.

    The same surname *is* indicated by the test results.

    (The MRCA was born in 1858 and died in 1922, so no exposure to freakish levels of radiation occurred to mutate DNA faster, lol).

    Any assistance is appreciated.

  • #2
    A 61/67 match between 2nd cousins, once removed does seem excessive. But remember that calculations of "time to most recent common ancestor" (TMRCA) are based on mutation rate averages. Some paternal lines have a higher rate and others have a lower rate. Those who are at the extremes on either end are "outliers." That's probably going on in your situation.

    There are a couple of things you can do.

    Probably the most decisive test would be Family Finder. If the two men are actually 2nd cousins, once removed, they would share enough autosomal DNA to be able to confirm that. It's a close enough relationship that over 90% of 2nd cousins, once removed share enough DNA to be recognized as a match. If they are no match or a distant match, then you're probably looking at a different cousin relationship than you think.

    Also, both men could order the appropriate SNP pack test to make sure that they're in the same haplogroup/subclade. But that would be more expensive than Family Finder and not as definitive.

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    • #3
      Originally posted by Uncle Lucifer View Post
      Just got results back for a 67-STR y-DNA test that showed a genetic distance of 6 between the donor and an individual who is a known second cousin, once removed.
      which markers do they differ on?

      Comment


      • #4
        Originally posted by Uncle Lucifer View Post
        Just got results back for a 67-STR y-DNA test that showed a genetic distance of 6 between the donor and an individual who is a known second cousin, once removed.
        One possible cause of this is a recLOH -- a single mutation which causes simultaneous changes in DYS459, DYS464, and CDY.

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        • #5
          Originally posted by lgmayka View Post
          One possible cause of this is a recLOH -- a single mutation which causes simultaneous changes in DYS459, DYS464, and CDY.
          Do you mean a single mutation caused simultaneous mutations in 3 different markers, or that perhaps one mutation in each of those multi-copy markers caused differences in each copy? I'm confused.

          Comment


          • #6
            Thanks for all the replies. Here are the values. The basic group is R1a:

            STR Modal Donor 1 Donor 2

            DYS449 33 33 32
            Y-GATA-H4 12 11 12
            DYS456 17 18 17
            DYS481 23 24 23
            DYS487 13 13 15

            Donor 1 is a male first cousin of mine, Donor 2 is a second cousin once removed from Donor 1 and me.

            MRCA lived from 1858-1922, three generations from Donor 1, four generations from Donor 2.

            Thanks again.

            -L.

            Comment


            • #7
              Originally posted by Uncle Lucifer View Post
              Thanks for all the replies. Here are the values. The basic group is R1a:

              STR Modal Donor 1 Donor 2

              DYS449 33 33 32
              Y-GATA-H4 12 11 12
              DYS456 17 18 17
              DYS481 23 24 23
              DYS487 13 13 15

              Donor 1 is a male first cousin of mine, Donor 2 is a second cousin once removed from Donor 1 and me.

              MRCA lived from 1858-1922, three generations from Donor 1, four generations from Donor 2.

              Thanks again.

              -L.
              The post by lgmayka offered a possible explanation, which I hadn't considered. When two men who are fairly close cousins by paper trail research have a greater genetic distance than normally expected, you should look at the multi-copy markers mentioned by lgmayka as involved in recLOH events.

              However, from what you've reported in this post, none of those markers are involved. So, the unexpected genetic distance (61/67) is not due to a recLOH.

              Go back to my post of yesterday afternoon for the explanation I offered, along with the suggestion for both of you to order Family Finder to confirm the paper trail relationship of 2nd cousin, once removed.

              Comment


              • #8
                Originally posted by benowicz View Post
                Do you mean a single mutation caused simultaneous mutations in 3 different markers, or that perhaps one mutation in each of those multi-copy markers caused differences in each copy? I'm confused.
                Yes, recLOH refers to a single mutation event involving multi-copy markers on the same palindromic arm of the y chromosome. If you want more information than is in the short Wikipedia article that lgmayka linked to, read a slightly longer article by Thomas Krahn at http://www.dna-fingerprint.com/modul...rticle&artid=9. The article includes some useful diagrams to illustrate recLOH.

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                • #9
                  Originally posted by Uncle Lucifer View Post
                  Thanks for all the replies. Here are the values. The basic group is R1a:

                  STR Modal Donor 1 Donor 2

                  DYS449 33 33 32
                  Y-GATA-H4 12 11 12
                  DYS456 17 18 17
                  DYS481 23 24 23
                  DYS487 13 13 15

                  Donor 1 is a male first cousin of mine, Donor 2 is a second cousin once removed from Donor 1 and me.

                  MRCA lived from 1858-1922, three generations from Donor 1, four generations from Donor 2.

                  Thanks again.

                  -L.
                  DYS449, DYS456 & DYS481 are all fast mutating markers!

                  Comment


                  • #10
                    Originally posted by Uncle Lucifer View Post
                    Thanks for all the replies. Here are the values. The basic group is R1a:

                    STR Modal Donor 1 Donor 2

                    DYS449 33 33 32
                    Y-GATA-H4 12 11 12
                    DYS456 17 18 17
                    DYS481 23 24 23
                    DYS487 13 13 15

                    Donor 1 is a male first cousin of mine, Donor 2 is a second cousin once removed from Donor 1 and me.

                    MRCA lived from 1858-1922, three generations from Donor 1, four generations from Donor 2.

                    Thanks again.

                    -L.
                    This may not seem like a big deal, but the infinite allele method would return a GD of 5, not 6, because DYS487 is a two-step mutation.

                    Comment

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