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Determining relatedness & common ancestor based upon 48/67 correctly matched markers

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  • Determining relatedness & common ancestor based upon 48/67 correctly matched markers

    I am new to DNA genealogical studies and need some help in understanding the following. Recently I had to compare my own genealogy with the Lord of my clan. We each had 67 markers identified. Of the 67 markers there was 19 mismatches, and 48 correct DNA marker matches. In the first 37 markers there were 12 mismatches, and in the last 30 markers there were 7 mismatches. There are at least 21 generations since the first individual was named Lord of our clan. I understand that there are mutations, and wonder if these could account for the differences in our markers. How do I or how can I calculate the degree of relationship when there is 48 of 67 markers that are matched. I may be wrong, but I think this means that there is enough genetic material to show there is a relationship, but that the relationship exists further back in our generations, i.e., 20 generations versus 4 generations. Also, how do I calculate the likelihood, based upon percentages, of a common ancestor in each generation? Thank you.

  • #2
    You could use McGees Y comparison utility;
    http://www.mymcgee.com/tools/yutilit...ode=ftdna_mode
    You can choose % probability and generation vs years, FTDNA mutation rates or more conservative McDonald rates.
    Remember these are only guides.

    If you are both in a FTDNA Surname project, the Admin should be able to give you the % Probability up to 24 generations.

    I have 2 men in one of my projects with a Genetic Distance of 19 at 67 markers.
    This is what the FTDNA TIP has for as % probability of them having a common ancestor within so many generations.;
    4 generations is 0.00%
    8 generations is 0.00%
    12 generations is 0.08%
    16 generations is 0.98%
    20 generations is 5.01%
    24 generations is 14.82%
    Last edited by rivergirl; 27 April 2009, 07:26 PM.

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    • #3
      25 ot of 37; 48 out of 67...

      My guess is that the patrilines converge thousands of years ago, long before the clans we know today had been established.

      What about the haplogroup? Get a deep SNP test done & see if the two subjects belong to the same deep haplogroup.

      Timothy Peterman

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      • #4
        Another tool is http://dna-project.clan-donald-usa.org/tmrca.htm

        Assuming your two cases are in the same haplogroup, then the calculator suggests you are most likely related about 60 generations ago.

        Choose any generation length you like, and multiply by 60.

        25 years X 60 = 1,500 years.

        Regards,
        Jim

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