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How often will 5 generation cousins have "only" 36 of 37 marker match?

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  • Jim Barrett
    replied
    Mutations can occur at any time and on any marker. It doesn't matter if it is a fast or a slow mutating markers. Father and son or two brothers could easily match only on 11 of 12 markers.

    Take 10 coins, shake them up and drop them on the floor. Averages, this is what mutation rates are based on, tell us you should have five heads and five tails. Try this 100 time and see how many time you get five heads and five tails.

    If you match on 36 on 37 markers you have a good match.

    Leave a comment:


  • spruithean
    replied
    Originally posted by Richard2267 View Post
    I have used Y-DNA to help prove my direct line male ancestors. I have strong genealogy paper trails for myself and a distant cousin, we are descendants of two different sons of our earliest known, direct line male ancestor, 4 and 5 generations back. We got a strong DNA match, but not perfect, 36 of 37 markers, and the mismatch was on CDYa. A genealogy friend has nearly the exact same thing, a solid paper trail from two sons of his earliest known direct line male ancestor, a 36 of 37 marker match, in his case the mismatch was on GATA H4. We were both sure we would have a match and, though we understand that these are strong matches that largely prove our paper trail, we were both a bit surprised we didn't get perfect matches.

    So, my question. If we are talking about a DNA match between two descendants who are known to be directly related 5 generations back (for the sake of argument let's assume there is absolute proof), about how often would we expect a 37 marker DNA test to result in a one off mismatch? One in ten, 1 in 20, 1 in 100?

    Also, what is the liklyhood that, where there is an "unexpected" mismatch such as the two outlined above, there might have been some ambiguity when analyzing the samples? Is there any doubt when reading these numbers or is it always cut and dry? If the reading at CDYa says 33 it's absolutely 33, and not just more likely 33 than 32 or 34?

    Thanks, Richard
    Richard, CDYa/b are fast mutators so really its nothing to worry about. A 36/37 match is a great match.

    Good luck in your searches.

    Leave a comment:


  • bob armstrong
    replied
    I have a proven paper trail back to the late 1690's, & was fortunate enough to find living descendants from three of the four branches which share a common ancestor in c1701.
    I was pleased to see that I matched 36/37 with them, & my miss was on fast-moving markers.
    Don't know if that helps
    Cheers
    Bob

    Leave a comment:


  • efgen
    replied
    Mutations are random occurrences and there's no way to precisely say when a mutation will happen, or how many generations back a particular mutation occurred. There are probabilities and confidence intervals, which you can read about here:

    http://www.familytreedna.com/faq-markers.aspx

    The owner of FTDNA is a 36/37 match with his father. Mutations have to happen sometime, and they always happen between a father/son pair. It's just a roll of the dice as to which father/son pair they will happen in, and at what marker.

    Elise

    Leave a comment:


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    Guest started a topic How often will 5 generation cousins have "only" 36 of 37 marker match?

    How often will 5 generation cousins have "only" 36 of 37 marker match?

    I have used Y-DNA to help prove my direct line male ancestors. I have strong genealogy paper trails for myself and a distant cousin, we are descendants of two different sons of our earliest known, direct line male ancestor, 4 and 5 generations back. We got a strong DNA match, but not perfect, 36 of 37 markers, and the mismatch was on CDYa. A genealogy friend has nearly the exact same thing, a solid paper trail from two sons of his earliest known direct line male ancestor, a 36 of 37 marker match, in his case the mismatch was on GATA H4. We were both sure we would have a match and, though we understand that these are strong matches that largely prove our paper trail, we were both a bit surprised we didn't get perfect matches.

    So, my question. If we are talking about a DNA match between two descendants who are known to be directly related 5 generations back (for the sake of argument let's assume there is absolute proof), about how often would we expect a 37 marker DNA test to result in a one off mismatch? One in ten, 1 in 20, 1 in 100?

    Also, what is the liklyhood that, where there is an "unexpected" mismatch such as the two outlined above, there might have been some ambiguity when analyzing the samples? Is there any doubt when reading these numbers or is it always cut and dry? If the reading at CDYa says 33 it's absolutely 33, and not just more likely 33 than 32 or 34?

    Thanks, Richard
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