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Comparing a half cousin to a possible full cousin

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  • Comparing a half cousin to a possible full cousin

    Good Evening Everyone,

    I have a current situation which I would request some input if possible. My father and his mother both have a past mentioned match.

    Match and Grandmother Share:
    65.13cM & 42.96 -> segment length

    Match and Father Share:
    62.02cM & 42.96 -> segment length

    On testing other relatives, my grandmother's known 1st half cousin - Martin: (They have same grandfather - Vines Hardeman).

    1st half cousin (Martin) & grandmother share:
    410.60cM & 62.40 -> segment length

    It turns out that the match and my grandmother's known 1st half cousin (Martin) are related.

    Match and 1st half cousin (Martin) share:
    134.01cM & 48.30 -> segment length

    It appears that the 134.01cM suggests a 2nd cousin once removed. Is it plausible to assume that the match is a FULL cousin to my grandmother's 1st half cousin - Martin? Also, is it plausible to assume the reason for the reported 65cM shared with my grandmother is due to the match being a FULL cousin being compared to my grandmother who is a half cousin to the same known 1st half cousin -> Martin?

    Or is the reported 65cM, merely due to the common ancestor simply being a bit further in the past?

    Thanks
    Steve
    Last edited by shandy4473; 14th February 2012, 12:49 AM.

  • #2
    Are the segments mentioned the only segment shares over 5 cM. The segment counts (for segments over 5 cM) can also be helpful in addressing the expected relationship.

    Comment


    • #3
      Steve:

      Is this person matching in the segement pool that your grandmother and Martin share? If you look at the map of Martin to Grandmother you see 410cM worth of segments. Is Match A falling inside that amount or outside or both?

      Matt.

      Comment


      • #4
        Check Your Email

        Hello Matt,


        Please check your email. I sent the photo to you. It looks like the match is falling in the segment pool, but the match may be outside too.

        Thanks
        Steve
        Last edited by shandy4473; 14th February 2012, 01:28 PM.

        Comment


        • #5
          You sure have the good puzzles.

          My first thoughts are that Vines has a half brother, the ancestor to MatchA or MatchA and Martin are 3rd cousins, not 2nd. If they are 2nd then they are probably half 2nd but nothing can be proven by just the numbers alone..

          The differences in the segments where some line and up and some do not point to a fact that the relation is by Vines and a sibling of Vines. The small amount of 130cM points to either a link farther back (i.e. 3rd cousins) or Vines and a half slbling of Vines are the ancestors for both. You see differences because the comparison between Martin and your grandmother have a common ancestor but the comparison of Martin to MatchA are by a different common ancestor; siblings.

          The small 42cM longest block for your grandmother and father to MatchA are partly due to the half sibilngship between your grandmother's mother and Martin's father and partly due to the fact that the common ancestor is the parent of Vines or grandparents of Vines.

          Matt.
          Last edited by mkdexter; 14th February 2012, 02:12 PM.

          Comment


          • #6
            Email

            Thanks Matt,

            What are your thoughts about the other emails?

            We can discuss in private?

            (And yes I have the puzzles LOL!!!!!!!!!!!)


            Steve

            Comment


            • #7
              Vines Hardeman is an ancestor of Martin

              Originally posted by mkdexter View Post
              But the comparison of Martin to MatchA are by a different common ancestor; siblings.
              Thanks Matt. Actually Vines is an ancestor of Martin and my grandmother. Vines was their grandfather. So the ancestor of MatchA and Martin is either a parent or grandparent of Vines. Vines's parents were David and Eliza Hardeman.

              Question - Is 130cM a large value for 3rd cousins? Wouldn't that hover around a 2nd cousin once removed or there is no way to tell?

              Steve

              Comment


              • #8
                Yes. It's in there for 3rd cousins.

                Martin to Vines is grandparent/grandchild so any other grandchild of Vines (who is not a sibling of Martin) is a 1st cousin to Martin.

                Vine's parents being common ancestors would make Match A and Martin 2nd cousins but the number cM is too low for most cases. Vine's grandparent's being in common would make Match A and Martin 3rd cousins and 130cM works for that. The only other explanation (by paper trail in your case stating the common ancestor is a sibling of Vines) is that Vines has a half brother and that would equate to a 130cM for 2nd cousins too.

                Matt.
                Last edited by mkdexter; 14th February 2012, 05:31 PM.

                Comment


                • #9
                  2nd Cousin Once Removed

                  Originally posted by mkdexter View Post
                  Yes. It's in there for 3rd cousins.

                  Martin to Vines is grandparent/grandchild so any other grandchild of Vines (who is not a sibling of Martin) is a 1st cousin to Martin.

                  Vine's parents being common ancestors would make Match A and Martin 2nd cousins but the number cM is too low for most cases. Vine's grandparent's being in common would make Match A and Martin 3rd cousins and 130cM works for that. The only other explanation (by paper trail in your case stating the common ancestor is a sibling of Vines) is that Vines has a half brother and that would equate to a 130cM for 2nd cousins too.

                  Matt.
                  Thanks Matt. What about a 2nd Cousin once removed relationship between MatchA and Martin. And thus MatchA's parent and Martin would be 2nd cousins. Would the 130cM be too low for a 2nd cousin once removed relationship? The reason I am asking is my dad shares 170cM with his 2nd cousin once removed and they are full 2nd cousins once removed. His mom shares 340cM with the cousin.
                  Last edited by shandy4473; 14th February 2012, 05:45 PM.

                  Comment


                  • #10
                    no that works too.

                    take the shared pool you start with..

                    here are some approximations (very rough estimates)

                    sibs = 2800cm
                    1st = 900cm
                    2nd = 300cm

                    A once removed is half that because you have to add one more incidence of recombination for once-removed.

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                    • #11
                      Okay cool

                      Okay cool Matt. Thanks.

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