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Ancestry's ThruLines vs MH Theory of Family Relativity

Discussion in 'DNA Questions and Answers' started by canadianbeth, Aug 3, 2019.

  1. canadianbeth

    canadianbeth LostCousins Member

    I am not sure if this is the correct place to put this; if not please move it to the correct one Peter.

    When looking at MH yesterday and the Theory section I found someone who is listed as a 5th cousin. However, working backwards to an apparent 4th great-grandfather, the name does not match with the one I do have for my 4th great-grandfather at Ancestry. That line is proven, at least to my 3rd great-father; after that, I only have a name for his father and it is not the same as the one given at MH.

    The name for my 3rd GG is Francis Moss - it is listed as William Francis Moss for MH and only a 20% chance of them being the same person. His father is given as Robert; my Francis', according to Ancestry, was James. Looking at that, I would assume they are not; however another of Robert's sons is Hugh, and he is listed as 100% my 3rd great-granduncle. It is his descendant who is given as my 5th cousin and the match is 18.7cM, 2 segments.

    I can find no information at all on James at Ancestry, nor of Robert or the name given as his wife's. And Francis was born before GRO records so no joy there either. His daughter Mary Ann married my 2nd great-grandfather William Riches and I have found their marriage information, listing both their parents.

    I am wondering if maybe Francis' father James was the brother of Robert, which would make the relationships quite different of course; if K.M., was not my 5th cousin -what would she be? would the cM match still be correct?

    I only have 13 of these Theory matches and the rest all coincide with the information I already had; this is the only one that seems to be missing something, or someone.
  2. Tim

    Tim Moderator Staff Member

    Predicted relationships are calculated from the trees that both people load online. If one or both of the trees are incorrect then you will get some odd answers back. Also, Ancestry and MH use different predictions to work out possible relationships based on cM alone.
  3. Helen7

    Helen7 LostCousins Star

    Agreed. Also any predictions of possible relationships based on cM alone can only be very approximate, as the numbers vary massively once you get beyond about 2nd cousin. I have (documented) 5th cousins with higher cM than 3rd cousins.
    Last edited: Aug 5, 2019
    • Agree Agree x 1
  4. peter

    peter Administrator Staff Member

    I have a documented 8th cousin who does share a DNA segment, and know of documented 2nd cousins once removed who don't.

    In the latter case we initially suspected that the documentation was wrong, but other matches have proven that this is not the case.

    Every generation involves a random process, and all that randomness adds up!

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