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How Many Ancestors?

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  • How Many Ancestors?

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

    "We can give a simple answer by assuming that each chromosome is passed on intact, with a 50% chance of getting either one from a pair. This gives us a maximum of 44 genetic ancestors, and means that the probability of being related to any particular ancestor N generations ago is 1 – (1 – 0.5N – 1)22. We’d have about 43 genetic ancestors out of 1024 genealogical ancestors after 10 generations."

    "The probability of having DNA from all of your genealogical ancestors at a particular generation becomes vanishingly small very rapidly; there is a 99.6% chance that you will have DNA from all of your 16 great-great grandparents, only a 54% of sharing DNA with all 32 of your G-G-G grandparents, and a 0.01% chance for your 64 G-G-G-G grandparents. You only have to go back 5 generations for genealogical relatives to start dropping off your DNA tree."

  • #2
    You can offer that as a response each time someone is looking for a confirmation or a denial of ancestry beyond Family Finder timeframe.

    W.

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    • #3
      A better, that is, more detailed by including recombination, analysis finds that the number of ancestors we carry can be thought of around 800 to 1000, for any time back beyond the 10th generation.

      See: http://gcbias.org/2013/11/11/how-doe...ack-over-time/

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      • #4
        Originally posted by S9 H9 View Post
        A better, that is, more detailed by including recombination, analysis finds that the number of ancestors we carry can be thought of around 800 to 1000, for any time back beyond the 10th generation.

        See: http://gcbias.org/2013/11/11/how-doe...ack-over-time/
        10 generations back there wasn't 1000 people living within a 10 mile radius of where I was born.

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        • #5
          Originally posted by 1798 View Post
          10 generations back there wasn't 1000 people living within a 10 mile radius of where I was born.
          Are you saying you were born in the same locale as all your ancestors, for 10 generations?

          Even if that is true for you, for many people there were plenty of regional family groups that interbred from valley to valley, etc.

          And, your ancestors had legs. Maybe horses (if on a continent.) Or if need be, boats, rafts, etc.

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          • #6
            In plains, 20 km radius was the practical limit. With hills, less.

            A major river or any marshes were like impregnable borders to marriages.

            W.

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            • #7
              Originally posted by dna View Post
              In plains, 20 km radius was the practical limit. With hills, less.

              A major river or any marshes were like impregnable borders to marriages.
              You have to bear in mind that "the girl next door" at the time of marriage may have been born in a different region, country, or continent altogether. Or her parents weren't necessarily from the same region as her husband's parents.

              However, in some cases she may have lived close by to her future husband's close relatives and not close by to him. In others, she was only happened to be living close by where the raiding party/settlers came to shore.

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              • #8
                Originally posted by rbmirvin View Post
                You have to bear in mind that "the girl next door" at the time of marriage may have been born in a different region, country, or continent altogether. Or her parents weren't necessarily from the same region as her husband's parents.

                However, in some cases she may have lived close by to her future husband's close relatives and not close by to him. In others, she was only happened to be living close by where the raiding party/settlers came to shore.
                How can one person change the autosomal dna of a region?

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                • #9
                  One very important piece of information missing from this thread is how far back can 5cM, 7cM, 10cM, and 12cM segments go. Just because relatives stop sharing DNA at 5 generations doesn't mean that a segment can't go on for 10, 12 or 15 generations. It actually does. It just doesn't do it for all of our ancestors.

                  See the example fan chart by Blaine Bettinger to see how some DNA continues on and some drops off.

                  http://www.thegeneticgenealogist.com...-genetic-tree/

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                  • #10
                    Originally posted by rbmirvin View Post
                    You have to bear in mind that "the girl next door" at the time of marriage may have been born in a different region, country, or continent altogether. Or her parents weren't necessarily from the same region as her husband's parents.

                    However, in some cases she may have lived close by to her future husband's close relatives and not close by to him. In others, she was only happened to be living close by where the raiding party/settlers came to shore.
                    For centuries, a family could not just come to a village. There would be no place for them.

                    W.

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