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How to use DNA to Find info on paternal great grandmother's 3x great grandfather?

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  • How to use DNA to Find info on paternal great grandmother's 3x great grandfather?

    I am trying to figure out a way to use DNA, if at all possible, to track down information on my my paternal great grandmother's 3x great grandfather?

    In my family tree, my great grandmother and grandfather died at an early age, which resulted in my 2x great grandfather adopting their children and renaming them to his surname. This makes researching that surname difficult using DNA, at least as far as my limited knowledge goes. I have done both the Y67 and mt-DNA tests, but these are straight lines.

    Any ideas on how DNA can be used to find this information on my 6x great grandfather who is the 3x great grandfather of my paternal great grandmother?

  • #2
    Is your Grandmother still alive?
    If not are you able to test any of her siblings?

    DNA wise, for the best results, the ideal candidate to test would be herself, her siblings, or her children/nieces/nephews.

    The further the generations away from her, the greater the chance this ancestors DNA maybe lost and replaced by spousal lines.

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    • #3
      No my grandmother and all her siblings have passed. The closest I can get is her grandson or granddaughter.

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      • #4
        Originally posted by USMC7312 View Post
        Any ideas on how DNA can be used to find this information on my 6x great grandfather who is the 3x great grandfather of my paternal great grandmother?
        What information are you looking for?

        Jack

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        • #5
          To start what Hapologroup my 6th great grandfather is or more accurately what Hapologroup the male line is for my great grandmothers

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          • #6
            Originally posted by USMC7312 View Post
            To start what Hapologroup my 6th great grandfather is or more accurately what Hapologroup the male line is for my great grandmothers
            In order to find that specific ancestor's yDNA haplogroup, you'll have to find a known paternal line descendant (son, paternal grandson, paternal grandson's son, etc.) to test. Since the y chromosome is passed down from father to son with no recombination with the mother's DNA (she has no y chromosome to recombine), the only descendants of that ancestor who can give you his haplogroup would be a paternal line descendant. Since you don't know the indentity of your 6th great-grandfather, I don't see how you'll know who are his paternal line descendants.

            For the broader question of finding anyone with whom you have your 6x great grandfather (the 3x great grandfather of your paternal great-grandmother) as a common ancestor, that will be very difficult, almost close to impossible, using an autosomal DNA test. That type of test can only reliably find cousins out to about 3rd cousins. When you reach 4th cousins, only about 50% of them will share enough DNA for the test to find matches in the database. At 5th cousins, the test will only find about 10% of the 5th cousins in the database. This is because the recombination over many generations shortens or eliminates most large segments from specific ancestors, such that the test can't find many of the actual more distant cousins who may be in the database.

            Given that you're hoping to find 7th cousins (descendants of your 6th great-grandfather), most of any distant cousins in the database will be missed by the limits of the test.

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            • #7
              Your autosomal DNA had to come from someone 7 generations back, but the odds are very small that any particular 7 generation ancestor is represented in your genome. That's because the genome is transmitted from one generation to the next in several dozen chunks, rather than being chopped up into thousands of little bits. There has been some discussion of this phenomenon here. The bottom line: while it is unlikely that the ancestor you are looking for can be detected, there is still a possibility that a significant segment has been transmitted and can be detected. If you succeed, that's great, but if you don't, there's no clear way to know if your hypothesis about the identity of your ancestor is incorrect, or if you just don't happen to get any of his DNA!

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