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  • mutations

    What does it mean if I got an exact match at 25 markers then at 37 markers it shows a distance of -2 with the same person, but ftdna e-mail said there is a 99% likelihood that we share a common ancestor?

    How exactly does a mutation occur?
    Thanks for the input,

  • #2
    Mutations arn't supposed to happen, but they do.
    Some claim areas where they live, radiation, living habits, etc.
    Inbreeding is also bad.
    Get the 67 point test.


    • #3
      Probably the best explanation you can get will be from the various tutorials on FTDNA's website. Take a look at these and I think they will help answer your questions:

      The second link gives you information on what you can say about the relationship between two men who match either perfectly or closely at 37 markers. In your case there are differences on two markers. The tutorial in the second link says that in this case your line and the other line are definitely related.

      My best guess would be that the common ancestor probably lived within the last few hundred years, but it could have been within the last 200 years. Now you need to contact the close match and look for the common ancestor in your family trees, or at least a place and time where both of you had paternal line ancestors living.

      As far as how a mutation occurs, it's not known exactly why it occurs, just that when the DNA replicates itself, it makes a mistake and either adds or subtracts usually one sequence of chemicals called nucleotides at a specific location on the y. (This is called a "short tandem repeat" or STR - see So the son of the man who has had the mutation in the number of counts of the sequence at a certain spot gets that mutation from his father and passes it down to his sons, etc. By looking at the different counts of sequences at different markers, genetic genealogists can see where there's a fork in a paternal line and that two men are in different branches of the paternal line. Then an estimate, based on known mutation rates for specific STRs, can be made as to when the common ancestor of both branches from the fork lived.
      Last edited by MMaddi; 9 June 2010, 05:26 PM.


      • #4
        Thanks that does help clear up mutations so it is not necessarilary an adoption or a half brother etc. Just a fluke I guess.


        • #5
          A majority of the y chromosome mutations occur more frequently due to external environmental influences on the male gamete cells; one example, heat. Since in theory they should not occur they become easier to detect after long periods of time whereas autosomal DNA recombines too quickly to detect mutations in it.

          No it is most likely not an adoption when you see a genetic distance of two. A genetic distance of two means either two markers were one number different each or one marker was two numbers different. What that translates to is the two are probably related to a common ancestor yes but the question is how far back in time?

          The answer depends on first the genetic distance and second the actual marker(s) that is different. Some markers mutate (change) easier or faster than others.

          The best indicator to this is to rely on the built in FTDNATip information as it accounts for the genetic distance and the marker(s) which are different.

          The next thing to remember is there are cases where a father and son can be a genetic distance of two, it has happened. There are also cases where a genetic distance of 2 has occurred with two men hundreds of years apart to their common ancestor.

          As has been said, if you need to know a more refined indication on their distance to most common ancestor you will need to upgrade both of them to a 67 marker test. If you just needed to know if they were related to a common ancestor but don't care if hundreds of years vs. a few hundred then you really have that in the fact they are 37 genetic distance of 2.

          Getting more markers tested is like raising the power level of a microscope. You see a connection so then you dial in more power to see a better picture.. and so on.. the more markers tested, the clearer the picture will become.

          Another thought just occurred to me. If you have just one other match at 37-gd2 that may not tell you what you want to know if you are looking to verify a surname like I am. It is best to see a pattern of the same surname occurring multiple times with multiple close matches to be sure. In my case I have one close match but that person had something occur in his past lineage which resulted in a surname change - thus my search to verify my father's surname has to continue as he and my father will not have the same surname. So if this is the case with you too and you need to verify a surname for an adoption or something then look for more matches - but if you just wanted to test two known individuals to see if they were really related then you have what you needed.
          Last edited by mkdexter; 10 June 2010, 02:43 AM.