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Best test to find if my Mom's dad is her biological dad

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  • Best test to find if my Mom's dad is her biological dad

    I have built up a lot of info on my maternal grandfather's ancestors. However, recently some things are suggesting that he may not be my mother's biological father. Both are no longer living. I have second cousins, (descended from my grandfather's brother).

    Could I take a test and have it also taken by a cousin, that would tell me if we are biologically related? If so, which test would be best, and should I take it, (I'm female) or one of my brothers?

    I no very little about dna testing, so any information would be appreciated.

  • #2
    Autosomal DNA test

    You could both take an autosomal DNA test, like Family Finder from FTDNA that would tell you whether you share enough DNA to be 2nd cousins.


    • #3
      Best bet is probably the Family Finder test, which will pick up second cousin relationships quite clearly. If it fails to find a relationship, you have an answer.

      However, it might not be definitive if it does show a relationship. For example, if your "real" grandfather was a close relative of your mom's father, there's still a close relation between you and your second cousins, but not where you think it is.


      • #4
        Thank you & final question

        Thanks for this. Final question, does it make any difference whether it is me or my brother who takes the test?


        • #5
          No, not for this test. You and your brother will have slightly different results, as you each have a different mix of your mother's and father's DNA, but for testing against 2nd cousins the result shouldn't vary in any significant manner.


          • #6
            I think ideally your brother would be better and the best cousin would be a son of a daughter or your grandfather's brother. This would amplify the x chromosome which would have undegone 4 splits while the rest of your DNA underwent 6. Then you could take your ff raw files and load them to gedmatch and compare at the autosomal and sex chromosome level.

            Because of the odd way the x chromosome passes on it can provide extra clues. Your x was mixed with your father's so is slightly more diluted then your brother's. The difficulty would be determining if the father was one of his brothers. If you tested the grandson who happened to be the birth father there would be a large spike in shared DNA though. They'd go from 2nd to 1st cousin. How many brothers are there? Is that a possibility? I would guess some other man would be more likely but all situations are different.


            • #7

              Just wanted to tell you the only close relative matces are my children and 1 cousin. He is my mothers first and my first once removed. He also showed up on my children's list 2-3 and he is their 1st twice removed. I was thrilled that it worked but sure it is because it is fairly close family. Hopefully if your related it will show and if not probably not related. The cm's for my match to him was in the 400's and about 197 for the you a gauge although it could be a bit of wiggle room.


              • #8
                Thx Osiris

                I didn't understand a lot of your post, but what I did understand makes sense,. I will have my brother tested rather than myself, and a second cousin rather than second cousin once removed. Boy, am I going to need some assistance interpreting the results, but hopefully Family tree can help with that.

                There is almost no chance that my grandfather's brother could be the father. The boys were adopted at an early age by different parents, raised separately, and there was very limited contact. In the relevant time frame,my mother's parents were in Chicago living a bohemian lifestyle (the twenties, bath-tub gin, grandmother played honkytonk in a speak easy, grand-father was stage manager at a vaudeville theatre), while his brother was living in South Western Ontario, attending church and ploughing the land.


                • #9
                  Be sure to post back to this thread when you have results!