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  • Try to lean to the left or start on top

    While we are waiting for FTDNA to go live with X chromosome segment (SNP) matching, best to discuss more fun facts.

    People often ask where to start when they are matched with a cousin on the X chromosome and you have no idea how you are related. The goal is to find a most recent common ancestor (MRCA) with that cousin that falls within the X pattern of inheritance. So best to look at math probabilities first.

    As the percentage of ancestral X chromosome participants decreases as you go back in time, what happens to the probabilities? Do all the X participants 7 generations back in your pedigree have an equal chance of giving you an X segment? Absolutely not. Some have a much, much greater chance than others even though they all fall within the X pattern of inheritance in the same generation. Did you know that you have some favored X ancestors in each generation? The more males in the path from the ancestor down to you, the higher the chance of getting an X segment from that line. This is because the segments do not get cut up through recombination.

    That doesn't mean you will get an X from these males. Some people like my mother gave me her mother's X and for some reason she hardly mixed it in with her father's X at all so that entire X lineage was lost to me in one fell swoop. I have to depend on my siblings to see the segments coming from my maternal grandfather since my parents are deceased. So much for probability...

    Well, lets get back to the math probabilities anyway even if you can't depend on math in real life to do what you want it to do sometimes. For many people, the probabilities can often lead you in the right direction so you don't waste as much time.

    http://www.thegeneticgenealogist.com.../NewChart5.jpg shows some probabilities. One fifth great-grandmother has a 1 in 8 chance but another male and female in that same generation only have a 1 in 64 chance each of making contributions to your X. The difference becomes even greater as you go back in time. The 5th great-grandmother who gave you her entire mitochondrial DNA really doesn't have the same advantage when it comes to being a participant in your X chromosome contribution. Remember that the mitochondrion and the X chromosome are inherited entirely separately. There is a very high chance the X will be broken up and/or lost when it passes through several females. So the mitochondrial all-female path becomes less and less important for the X chromosome as you go back in time. The lines that show male-female-male-female etc. have a higher success rate for X chromosome survival as a general rule.

    The X chromosome pedigree can be very helpful in knowing where to start. You want to find a MRCA (or ancestors) when you have an X matching segment with a newly-identified cousin. Check the probabilities first and concentrate on those lines to the left in Blaine Bettinger's fan chart where the fathers are listed to the left of their female mates.

    Lean to the left...

    Or if you want to follow a horizontal pedigree chart with the males listed on top, aim for the line on top as you read left to right following the X-inheritance pathway. See Deb's Delvings here:
    http://debsdelvings.blogspot.com/201...ce-charts.html

    This is just a suggested approach and you may find it impossible to connect with a distant cousin's pedigree. There is a reasonable chance your connection is with that 10th great-grandparent who had an amplified 1 in 64 probability of giving you a contribution. If this cousin also has an autosomal match with you, your chances are higher that there is a much more recent MRCA. Nobody can really make a prediction based on the size of the segment on just one X chromosome in isolation.

    Kathy

  • #2
    Kathy,

    Thanks for that fascinating post!

    I am aware of the x chromosome inheritance pattern as shown in Blaine Bettinger's helpful diagrams for x inheritance in men and women. But I had never thought of the difference in probability that specific ancestors have in contributing to my x.

    As a man, "leaning to the left" means that I should look to my maternal grandfather's ancestors as more likely to be involved in contributing to a shared segment on the x. That's very useful information.

    Comment


    • #3
      So, for a woman...

      So, we should also look to paternal X-matches first? Would my father's mother's father, etc. have the highest probability?

      Comment


      • #4
        Interesting

        This is really interesting. I have a line I want the see how far back it holds, perhaps X-DNA phasing is the way to go about it? Here is the line:

        Code:
        
        
        Gregers mother might be a wife of Birger Jarl Magnusson, duke of Sweden
        http://en.wikipedia.org/wiki/Birger_Jarl
        
        26. [m]   0.0008 % = 1/131072 Gregers mother 
        25. [F]   0.0008 % = 1/131072 Greger Birgersson Folkungaätt
        24. [m]   0.0015 % = 1/65536  … Gregersdotter Folkungaätt
        23. [m]   0.0031 % = 1/32768  Margareta Philipsdotter Örnsparre
        22. [m]   0.0061 % = 1/16384  … Magnusdotter Tunasons ätt
        21. [F]   0.0061 % = 1/16384  Bengt Fadersson Sparre av Hjulsta och Ängsö
        20. [m]   0.0122 % = 1/8192   Märta Bengtsdotter Sparre av Hjulsta och Ängsö
        19. [m]   0.0244 % = 1/4096   Elin Andersdotter Årbyätten
        18. [m]   0.0488 % = 1/2048   Dorotea Pinnow
        17. [m]   0.0977 % = 1/1024   Bengta Bülow
        16. [F]   0.0977 % = 1/1024   Nils Jönsson i Hå Halvhjort av Älmtaryd
        15. [m]   0.1953 % = 1/512    Ingrid Nilsdotter Halvhjort av Älmtaryd
        14. [m]   0.3906 % = 1/256    Elin Håkansdotter Båt af Billa
        13. [m]   0.7812 % = 1/128    Anna Olofsdotter Hwith
        12. [F]   0.7812 % = 1/128    Lindorm Stråle af Ekna
        11. [m]   1.5625 % = 1/64     Magdalena Stråle af Ekna
        10. [m]   3.125  % = 1/32     Malin Enhörning
        09. [m]   6.25   % = 1/16     Helena Gyllennieroth
        08. [F]   6.25   % = 1/16     Otto Strömsten
        07. [m]  12.5    % = 1/8      Cathrina Gustafva Strömsten
        06. [F]  12.5    % = 1/8      Johan Gabriel Gadd
        05. [m]  25.0    % = 1/4      Märtha Johansdotter
        04. [F]  25.0    % = 1/4      Johan Alfred Johannesson
        03. [m]  50.0    % = 1/2      grandfathers mother
        02. [F]  50.0    % = 1/2      grandfather
        01. [m] 100.0    % = 1/1      mother
        00. [F] 100.0    % = 1/1      me
        
        The line most probably will break, but I whould like to find out where

        Any ideas what test/tests I should go on taking first on myself? So far I havn't got any DNA-results for me or any of my ancestors/relatives. I have ordered Y-DNA111 och FF, what is the first step in X-DNA?

        Comment


        • #5
          Originally posted by PeterLarsen View Post
          This is really interesting. I have a line I want the see how far back it holds, perhaps X-DNA phasing is the way to go about it? Here is the line:
          Remember, the way recombination and assorting of chromosomes into gametes work, that you start to lose ancestors (from your DNA) after a while as you go back in time. While the X undergoes fewer recombinations per century (because of father-daughter inheritance) than its size would otherwise imply, eventually you will lose ancestors on the X also.

          Comment


          • #6
            Originally posted by S9 H9 View Post
            Remember, the way recombination and assorting of chromosomes into gametes work, that you start to lose ancestors (from your DNA) after a while as you go back in time. While the X undergoes fewer recombinations per century (because of father-daughter inheritance) than its size would otherwise imply, eventually you will lose ancestors on the X also.
            That makes sense. I am experiencing trouble grasping the application for X, but it should be an interesting addition to standard Y, mtDNA and autosomal comparisons. Perhaps it works best to study in combination with autosomalservices as Familyfinder?

            Comment


            • #7
              Originally posted by PeterLarsen View Post
              This is really interesting. I have a line I want the see how far back it holds, perhaps X-DNA phasing is the way to go about it? Here is the line:

              Code:
              
              
              Gregers mother might be a wife of Birger Jarl Magnusson, duke of Sweden
              http://en.wikipedia.org/wiki/Birger_Jarl
              
              26. [m]   0.0008 % = 1/131072 Gregers mother 
              25. [F]   0.0008 % = 1/131072 Greger Birgersson Folkungaätt
              24. [m]   0.0015 % = 1/65536  … Gregersdotter Folkungaätt
              23. [m]   0.0031 % = 1/32768  Margareta Philipsdotter Örnsparre
              22. [m]   0.0061 % = 1/16384  … Magnusdotter Tunasons ätt
              21. [F]   0.0061 % = 1/16384  Bengt Fadersson Sparre av Hjulsta och Ängsö
              20. [m]   0.0122 % = 1/8192   Märta Bengtsdotter Sparre av Hjulsta och Ängsö
              19. [m]   0.0244 % = 1/4096   Elin Andersdotter Årbyätten
              18. [m]   0.0488 % = 1/2048   Dorotea Pinnow
              17. [m]   0.0977 % = 1/1024   Bengta Bülow
              16. [F]   0.0977 % = 1/1024   Nils Jönsson i Hå Halvhjort av Älmtaryd
              15. [m]   0.1953 % = 1/512    Ingrid Nilsdotter Halvhjort av Älmtaryd
              14. [m]   0.3906 % = 1/256    Elin Håkansdotter Båt af Billa
              13. [m]   0.7812 % = 1/128    Anna Olofsdotter Hwith
              12. [F]   0.7812 % = 1/128    Lindorm Stråle af Ekna
              11. [m]   1.5625 % = 1/64     Magdalena Stråle af Ekna
              10. [m]   3.125  % = 1/32     Malin Enhörning
              09. [m]   6.25   % = 1/16     Helena Gyllennieroth
              08. [F]   6.25   % = 1/16     Otto Strömsten
              07. [m]  12.5    % = 1/8      Cathrina Gustafva Strömsten
              06. [F]  12.5    % = 1/8      Johan Gabriel Gadd
              05. [m]  25.0    % = 1/4      Märtha Johansdotter
              04. [F]  25.0    % = 1/4      Johan Alfred Johannesson
              03. [m]  50.0    % = 1/2      grandfathers mother
              02. [F]  50.0    % = 1/2      grandfather
              01. [m] 100.0    % = 1/1      mother
              00. [F] 100.0    % = 1/1      me
              
              The line most probably will break, but I whould like to find out where

              Any ideas what test/tests I should go on taking first on myself? So far I havn't got any DNA-results for me or any of my ancestors/relatives. I have ordered Y-DNA111 och FF, what is the first step in X-DNA?
              You only need to have the FF test to be able to view the new X browser as an advanced tool at FTDNA due to be released in 2014.

              Comment


              • #8
                Any ideas what test/tests I should go on taking first on myself? So far I havn't got any DNA-results for me or any of my ancestors/relatives. I have ordered Y-DNA111 och FF, what is the first step in X-DNA?[/QUOTE]

                Originally posted by Kathy Johnston View Post
                You only need to have the FF test to be able to view the new X browser as an advanced tool at FTDNA due to be released in 2014.
                By the way, make sure you don't order the separate STR test that is associated with the X chromosome that is offered by FTDNA. It will not match you with cousins.

                Comment


                • #9
                  Originally posted by Kathy Johnston View Post
                  You only need to have the FF test to be able to view the new X browser as an advanced tool at FTDNA due to be released in 2014.
                  Great news! That will be really interesting!

                  I wish there will be future services where ancestors in the uploaded GEDCOM-tree have a X-mark, and also that members have the option to mark surnames with an X, if they are possible X-DNA ancestors . That way matching someone on the X-chromosome can also match geographic locations and/or surnames (X-chromo subgroup) making the match more meaningful.

                  Further there could be more types of projects, like:

                  X-chromo surname projects, where any of a members X-chromo ancestors can have the surname.

                  X-chromo geo projects, where any of a members possible X-chromo ancestors can be from a geographical location to join. The geo areas can then be smaller scale than country-size as todays geo projects where one is limited to the most distant paternal/maternal lines only (well, not all geo projects are that restricted, but most of them).

                  A calculated procentual chance of having inherit X-chromo DNA for the ancestors in question could also be attached to the GEDCOM-tree.

                  Perhaps I should continue on in the suggestions-section of this forum?

                  Now I hold my breath and wait to see what you already have planned for this, and refine my suggestions after that

                  Comment

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