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How are we related?

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  • How are we related?

    My sister and I have recently (independently) has our DNA tested and have both had the same match 1 - 2nd cousins with someone. Mine was 577 cMs and my sister was 608 cMs. I have managed to find out that the other person's grandfather, my generation, was a neighbour that we knew very well but did not know we were related. My grandmother's 2nd husband and his grandmother were brother and sister but as my grandmother married him in later life after the death of her first husband we are positive there were no issue from that relationship. So only a relationship by marriage.

    What I would like to know is what is the relationship between this girls grandfather and me. I researched both sides of both families and as yet, not come up with a connection but it is obviously there. Is it just between her grandfather and us or is it between his siblings and us as well. If I can pursuade one of them to take a test, which would be better?

    I hope this is clear as it is very confusing to me but Ihope someone with more knowledge can help.

    Thank you

  • #2
    The genetic evidence you have so far isn't enough to establish the exact relationship. There is a very handy chart that you can find by a Google search, "DNA Detectives Autosomal Statistics Chart". I highly recommend it!

    One thing that can be ruled out right now is that you and your match are NOT 2nd cousins. The amount of shared DNA with full 2nd cousins will be in the range of roughly 75 to 360 cM. So, you and your sister are closer than that to your match. However, the range of possibilities is quite large: 1st cousin, half aunt/uncle with half niece/nephew, 1st cousin once removed, half 1st cousin, and a couple others that would usually involve a significant age difference.

    Your task is to take the information you already have (including the traditional genealogical information, such as ages, places of birth, where they have lived throughout their lives, and anything else you can discover about them) and use it to sketch out ALL of the possible family trees. Then you attempt to find additional information (from genetic testing and any other sources you can find) that will allow you to begin to rule out one or more or the possible family trees, until there is only one left, presumably the correct one.

    You should check right now to see if there is a significant match on the X chromosome (say, at least 10 cM), and you should check whether there are other matches that share one or more of the longer segments that you and your sister share with your new match (i.e., you are looking for matches that share a common ancestor all three of you). You should be able to use the data from additional matches to work out whether the new match is from your father's or from your mother's side of your family.

    Yes, it will probably be helpful to test additional relatives of your new match, but it will also be useful to test your own relatives (1st cousins, aunts/uncles from BOTH sides of your family) in order to work out what part of your own family tree connects with your new match. The more fairly close relatives that are tested, the more constraints are placed on the possible family trees. With enough people tested, there may be only one possible solution. Sometimes these things take time, sometimes you just have to wait until the right match or the right document surfaces, but with enough patience and persistence, it is very likely you will find the answer.


    • #3
      My First assumption based on info you provided, is that relationship between you and match is Half Great-Aunt / Uncle Half to Half Great-Niece / Nephew
      That you and her grandparent are half siblings (your father being his father since both you and sister match his granddaughter)

      But there are a few other possibilities as well, see following images

      Attached Files


      • #4
        Hi John,

        Thank you for your in depth reply. I am slowly going through the match's family tree but as she has been very reluctant to reply to anything I have asked her, although claiming she wants to know more, I am making some headway by speaking to the brother of her grandfather and researching on various sites available to me. It will be a long job but I will keep at it.

        I too am of the opinion that the relationship is closer than that of 2nd cousin (that is the label given by Ancestry) but it will be a process of elimination I think. I really wonder if the grandfather is a half brother because of the proximity of my father to his mother at the time he was born. (He was lodging just down the road) I must admit though, that he looks more like his father than mine. I hope to get some positive reaction to my request that he or one of his brothers takes a test. He may not want to know of course. Not an easy question to ask but as we are all getting on in years, it is an important one. If his brother takes a test and does not match with me, then I can be fairly confident that the brother rin question is a half brother.

        I have no aunts and uncles left now and only a few cousins many of whom are not interested in the family tree. I have asked one and he is so undecided about the privacy angle that I don't know if I can pursuade him. I wish I could afford to offer to pay for them all then that might make a difference.

        I have added my test to Gedmatch but I cannot get the other match to do the same. It seems she has lit the touch paper and retired. It is down to me to find the connection.

        Thanks again for your helpful reply, it is much appreciated.


        • #5
          Prairie Lad,

          Thanks for your reply. It is the conclusion that I too am arriving at which does narrower down research a bit. It is a bit of a shock as we were quite close neighbours and good friends, I am happy with it but I don't know how the grandfather will react if he finds we are half siblings.

          Thank you for those two charts which do indicate the possibilities quite clearly and will be helpful to me.

          Thanks again for your help.


          • #6
            Hi Prairie Lad,

            I have been giving my problem a lot of thought, even when I am not conscious of doing so and am no further forward. I have suggested to the brother of the match's grandfather about doing a DNA test but nothing came back. I will have to offer to pay for a test in the hope it will work and one of them will be willing to test. I cannot let it go now unless I am told by the grandfather to do so. I don't think he even knows as his granddaughter gave me the impression, she did not know who he was.

            You stated in your last post that the connection was on my father's side as both my sister and I match with the other person. It is my gut feeling too but how are you so sure. If it is confirmed to be the case, then that will automatically rule out 50% of the possible connections on my tree.

            I find all this DNA business hard to follow, so please forgive me if I ask stupid questions.