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  • Longest survived dna segment

    As things are slow and I haven't had any new matches since the 3rd thought I would make a post.

    Is this possible or anyone else have such an experience:

    On chromo 12 I have a shared segment match of 75.7 cm who turned out to be my 5th cousin 1r. Our common ancestor was born 1735.
    Along this segment I have worked out a total of 6 matches within the segment

    Match A, 75.7 cm, 5th cousin 1r
    Match B, 42.8 cm, 4th cousin 3r
    Match C, 16.5 cm, sibling of A
    Match D, 14.9 cm, 4th cousin 1r
    Match E, 12.5 and 2.4 cm, 5th cousin 1r
    Match F, 11.2 cm, 6th cousin

    All the above descend from same common ancestor born 1735 except match F who descends from his brother.
    In addition I have 32 in common matches to match A within the segment. These vary between 40 and 5 cm. 13 of these have trees with short branches or just don't line up.
    Maybe a case of recombination but in my case the common ancestor shows once on my known tree. I have a few short branches on my tree and all the lines I have worked out are Colonial America.

  • #2
    Good question. Don't know the answer but it's a subject I have been giving some thought of late in relation to trying to understand how few genetic ancestors we may have.

    Most of us are probably familiar with this subject..

    http://www.genetic-inference.co.uk/b...share-our-dna/

    But then my mother got a match with a largest cm above 37cm that seemed to go back more than 200 years and then she got another unconnected one also above 37cm also seemingly from more than 200 years ago. How many more will come along in the future. It got me thinking that maybe we have far fewer genetic ancestors at the 10th generation and earlier than we suspected, perhaps much less than the 120 ancestors or so we used to think we had inherited DNA from, and perhaps those that we do inherit from go back much further in time than we originally thought.

    Earl.

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    • #3
      I am glad you put in the relationships rather than just years. Generations can be short or long. I have third cousins with our common great great grandfather born before the Constitution.

      Only the top two in your list are low odds of happening. The segments in the 10-16 cM range are common for that range of relationships. My cheat sheet says the odds for the 40 cM segment at that range are still around 4%. The sibling with the 75 cM match vs the one with the 16 cM match is a real wild card. Very long odds or some other factor.

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      • #4
        Related to this question, I have a really odd single-segment match of 91 cM on chromosome 1 with someone who, for the life of me, I see no relation possibly closer than six or seven generations back. This is the only segment above 5 cM that matches at all. There seems to nothing at all elsewhere -- that big matched segment is just sitting there all by itself.

        I'm not sure what to make of this.

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        • #5
          Originally posted by JohnG View Post
          Generations can be short or long. I have third cousins with our common great great grandfather born before the Constitution.
          Yes, in my case I am 51, my father was born 1899 and his father was born 1852! The matches I refer to are in my 1852 grandfathers line.

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          • #6
            Originally posted by rd11 View Post
            Related to this question, I have a really odd single-segment match of 91 cM on chromosome 1 with someone who, for the life of me, I see no relation possibly closer than six or seven generations back. This is the only segment above 5 cM that matches at all. There seems to nothing at all elsewhere -- that big matched segment is just sitting there all by itself.

            I'm not sure what to make of this.
            It might be a genetic persistence jackpot (1 in ten thousands or hundreds of thousands odds), a sign of lots of ancestors from a common pool, or an indication that the paper trails of one or both people are not quite right. One of my matches had the latter happen.

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