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  • My matches & my brothers matches

    I am a bit confused: (Important note I administer my brother's account.) My brother has a match that is a 2nd to 4th cousin match -- I do not have this person as a match at all -- so the person in question who matches my brother matches him on chromosome 19 at 46.95cm. I match my brother (on all chromosomes of course) on chromosome 19 at 59.73cm.

    Just looking at it, it looks like I should match this individual also. I do understand that my brother has matches that I don't have and that our dna is not exactly alike. I just find it confusing when one of us has a match that the other doesn't have and yet when I look at the chromosome browser it looks like we should both match.

    I hope this post isn't too confusing. I have tried to find a way to explain it to have it make sense.

  • #2
    While in your brother account, could you please select yourself and that person, then go to the chromosome browser.

    Do you see yourself and that person in the same place on chromosome 19? There is over 99cM in ch 19, so you could be in the same place or only partially overlap.

    Mr. W

    Comment


    • #3
      We each have two of each chromosome, a maternal one and a paternal one. 23 pairs, 46 single chromosomes.
      Chromosome browsers merge the two into one due to nature of testing can not distinguish between the two(which is which).

      Where siblings share DNA they will be either,
      1)Half base pair matching, only matching on their maternal or paternal chromosome, Sharing DNA from the same maternal or paternal Grandparent on one of the single chromosomes and inherited the opposite grandparents on the other.
      ie) Each share paternal Grandfathers DNA of paternal chromosome, and One received maternal Grandmother and the other received maternal Grandfather of their maternal chromosome.
      2)Full Pair matching, matching on their maternal and paternal chromosomes. Sharing DNA of the same Paternal Grandparent and the same Maternal Grandparent.
      ie) Both received Paternal Grandmothers DNA on paternal chromosome, and both received maternal Grandmother on their maternal chromosome.
      3)No matching. Each received the opposite paternal Grandparent and each received the opposite maternal Grandparent.

      In your instance with this match it would be that you and brother are Half base pair matching ie matching on say maternal chromosomes, and each inherited opposite say paternal grandparent on paternal chromosomes. Match is matching brother on paternal chromosome in which you receive the DNA from opposite paternal grandparent.
      Above is hypothetical as to which maternal or paternal chromosomes you are sharing with each other and which maternal or paternal chromosome this match is matching brother on.

      Half and full base pair matching can not be seen on FTDNA, but if you utilize Gedmatch and use one to one with Graphic you will see areas that you share half or full base pair matching with brother. Full base pair being displayed as larger solid chunks of Green
      Last edited by prairielad; 2 November 2017, 03:58 PM.

      Comment


      • #4
        Originally posted by prairielad View Post
        We each have two of each chromosome, a maternal one and a paternal one. 23 pairs, 46 single chromosomes.
        Chromosome browsers merge the two into one due to nature of testing can not distinguish between the two(which is which).

        Where siblings share DNA they will be either,
        1)Half base pair matching, only matching on their maternal or paternal chromosome, Sharing DNA from the same maternal or paternal Grandparent on one of the single chromosomes and inherited the opposite grandparents on the other.
        ie) Each share paternal Grandfathers DNA of paternal chromosome, and One received maternal Grandmother and the other received maternal Grandfather of their maternal chromosome.
        2)Full Pair matching, matching on their maternal and paternal chromosomes. Sharing DNA of the same Paternal Grandparent and the same Maternal Grandparent.
        ie) Both received Paternal Grandmothers DNA on paternal chromosome, and both received maternal Grandmother on their maternal chromosome.
        3)No matching. Each received the opposite paternal Grandparent and each received the opposite maternal Grandparent.

        In your instance with this match it would be that you and brother are Half base pair matching ie matching on say maternal chromosomes, and each inherited opposite say paternal grandparent on paternal chromosomes. Match is matching brother on paternal chromosome in which you receive the DNA from opposite paternal grandparent.
        Above is hypothetical as to which maternal or paternal chromosomes you are sharing with each other and which maternal or paternal chromosome this match is matching brother on.

        Half and full base pair matching can not be seen on FTDNA, but if you utilize Gedmatch and use one to one with Graphic you will see areas that you share half or full base pair matching with brother. Full base pair being displayed as larger solid chunks of Green
        And the above applies to "chunks" (segments of the chromosomes) too. Siblings (full siblings) can have any of the above scenarios on different segments of any chromosome.


        Mr. W
        Last edited by dna; 2 November 2017, 04:02 PM.

        Comment


        • #5
          (Edited)Following attachment may give you a better visual and understanding of my above post. Due to the random recombination of parents chromosomes pairs, each child is a different random mixture of Grandparents, and how it results in Full, half or no match to each other.
          Attached Files

          Comment


          • #6
            I get so frustrated when something goes over my head. One of my favorite things to do is research and figure stuff out - most people hate it, but I love it, no matter the subject even if it is dry and boring. This dna business, however, ZOOM! Complete fly by!

            OK, I am really trying to understand. Here are a couple of screen shots. One from the chromosome browser on ftdna. This was from my brothers account. I am the blue line and the individual in question is the orange line. I was going to post it differently - but out of concern for this persons privacy I thought this would be the best way.

            The second and third screen shots are ftdna the little explanation you get when you mouse over the color on the chromosome browser and the last screenshot is from gedmatch. It shows the one-to-one comparison between me and my brother on chromosome 19.

            I read your explanation prairie, but...zoom. This is really making me feel stupid! Ask me about law...or history...or British Literature...or useless trivia, that is where I really shine
            Attached Files
            Last edited by Sis65; 2 November 2017, 04:49 PM.

            Comment


            • #7
              I am an amateur too, and I agree: genetics is extremely complicated.

              If that person is matching your brother only on Chromosome 19, then the Chromosome Browser gave you the answer. You are possibly matching that person only for as little as 8 cM, which would be below the threshold of 9 cM (I think it is 9cM...).


              Mr. W

              P.S.
              I think there is a tool that would tell you how many centiMorgans are in any defined region, but I am drawing blank here. I do not use it.
              Last edited by dna; 2 November 2017, 05:03 PM.

              Comment


              • #8
                This is an over-simplification: Your mother has 2 of each chromosome, one that she got from her father and one that she got from her mother. Her egg cells will have one or the other not both. You happened to get the one she got from one parent, but your brother got the one she got from her other parent and that's why this person matches your brother, but not you.

                Usually, the chromosome your mother got from her father will swap a segment or two with the one she got from her mother. This is called recombination. Occasionally it doesn't occur.

                The same thing applies to your father's chromosomes. Each sperm carries either the chromosome he got from his father or the one he got from his mother, or more likely a chromosome that has undergone recombination. And that goes for all 22 pairs.

                In the mother the X chromosome behaves just like the other chromosomes (autosomes), but half of a man's sperm will have a Y chromosome and half will have an X chromosome. The X and Y can't swap segments.

                I recommend that you read The Family Tree Guide to DNA Testing and Genetic Genealogy by Blaine T. Bettinger.

                Comment


                • #9
                  This situation is perfect for the "TRIANGULATOR".

                  https://dna-explained.com/2017/10/21...-triangulator/

                  Comment


                  • #10
                    Well, we're going to have to forget about the Triangulator for a while because it's been pulled

                    Sis65 - these articles by Roberta Estes might help explain why your brother matches a cousin but you don't. Roberta writes in a very straightforward way, and avoids most of the technical language that makes us newbies' brains freeze
                    https://dna-explained.com/2014/02/19...l-inheritance/
                    https://dna-explained.com/2015/08/23...ritance-study/

                    The articles are from 2014 and 2015 but I think they're still valid. If I'm wrong on that, someone please put me right.

                    Also, as at late May 2016, a match had to meet one of these criteria: sharing a total of 20cM with at least one segment greater than 7.69cM; or sharing one segment of 9cM+ regardless of total cM. As far as I know, that's still the case.
                    Last edited by Fern; 3 November 2017, 04:12 AM. Reason: Clarity

                    Comment


                    • #11
                      Originally posted by Fern View Post
                      Also, as at late May 2016, a match had to meet one of these criteria: sharing a total of 20cM with at least one segment greater than 7.69cM; or sharing one segment of 9cM+ regardless of total cM. As far as I know, that's still the case.
                      In the absolute sense, two kits are either a match or not and in the process of determining that, they may or may not meet some arbitrary criteria to call them a match.

                      Autosomal DNA matching methodology is a long way from being perfected.

                      Jack Wyatt

                      Comment


                      • #12
                        Originally posted by Sis65 View Post
                        I get so frustrated when something goes over my head. One of my favorite things to do is research and figure stuff out - most people hate it, but I love it, no matter the subject even if it is dry and boring. This dna business, however, ZOOM! Complete fly by!

                        OK, I am really trying to understand. Here are a couple of screen shots. One from the chromosome browser on ftdna. This was from my brothers account. I am the blue line and the individual in question is the orange line. I was going to post it differently - but out of concern for this persons privacy I thought this would be the best way.

                        The second and third screen shots are ftdna the little explanation you get when you mouse over the color on the chromosome browser and the last screenshot is from gedmatch. It shows the one-to-one comparison between me and my brother on chromosome 19.

                        I read your explanation prairie, but...zoom. This is really making me feel stupid! Ask me about law...or history...or British Literature...or useless trivia, that is where I really shine
                        This is a little advanced but you can find out cM of overlap using following site.
                        http://compgen.rutgers.edu/map_interpolator.shtml

                        Using site, overlap cM is about 24cM, thus this person would show as a match (passes FTDNA minimum matching threshold) if they were matching you on the same single chromosomes that you are matching your brother. Since they do not show up on your matchlist, this means match is matching your brother on the opposite chromosome that you are matching him (the half base pair section, yellow of Gedmatch one to one)
                        Attached Files

                        Comment


                        • #13
                          Thank you Moberlydrake for your oversimplification It is much appreciated! And thank you Fern for the links. I looked through them this morning, but will read them more thoroughly later today with another cup of coffee!
                          I am glad, Mr. W. that you agree that it is complicated -- I would hate to be the only person not getting it!
                          I have lurked on a couple of dna forums that I have decided I would never join or ask questions simply because I have seen where a new member will ask what in my mind is a valid newbie question and they get torn to shreds by the so called experts. I don't think people should be humiliated because the don't understand something as complex as dna. That is why I post my question here everyone has been super helpful and has not made me feel bad about not understanding.
                          Thanks for all the responses!!
                          I am liking that triangulator idea; hopefully it will be back up and running soon, I would love to mess around with it.
                          **Thanks Prairielad -- I just saw your post and I am going to click on that link and see what I can learn.

                          Comment


                          • #14
                            Originally posted by Fern View Post
                            [----] Also, as at late May 2016, a match had to meet one of these criteria: sharing a total of 20cM with at least one segment greater than 7.69cM; or sharing one segment of 9cM+ regardless of total cM. As far as I know, that's still the case.
                            Anybody knows a place in familytreedna.com ( but not forums.familytreedna.com ) that says so?

                            I have looked through my "Project Administrator News" in the GAP and cannot see it there...


                            Thank you - Mr. W

                            Comment


                            • #15
                              Originally posted by dna View Post
                              Anybody knows a place in familytreedna.com ( but not forums.familytreedna.com ) that says so?

                              I have looked through my "Project Administrator News" in the GAP and cannot see it there...


                              Thank you - Mr. W
                              I do not believe FTDNA states what they use as their main matching criteria, but the basic criteria was determined by looking at testers results
                              -Only matches sharing 20cM or more were shown on match lists
                              -No longest segment under 7cM has being reported

                              As for the 9cM longest segment matches to be shown for those the do not meet to 20cM threshold, this was announce, for one, in an email to Group administrators when it came in effect. I remember getting email, but have deleted it. May be another group admin still retained it and will repy about it.

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