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X-DNA question - siblings same X as me?

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  • X-DNA question - siblings same X as me?


    My question has to do with the X-DNA. Since I (female) inherited X from both of my parents, wouldn't my 2 sisters have inherited the same 2 X's? I do not have any brothers.

    I know that I am not as advanced as many are in this. Thank you for taking the time to help me to understand!

  • #2
    I think I have figured out some more about this.

    The X from our mother would be "mixed" - so our X would not necessarily match. The X that we received from father would be the same, but not the part from mother.

    Since neither father or mother is living, we cannot know exactly what part is matching.

    Or, as sisters, we compare our X, and we can determine the part that we each received from father? Each of us would match exactly (all 3 matching) at the part we received from father, right?



    • #3
      Females have two X's
      one from father that will be identical as father only had one and it is passed on intact (no recombination) to all daughters.
      and one from mother that is a random recombination of her two.

      Chromosome browsers merge the two (each chromosome comes in pairs, a maternal and a paternal)

      Utilizing a site called Gedmatch and using their X one to one compare with graphic you can see which area of X sisters are matching on their maternal X chromosome, as it will be shown as full base pair matching(green), which means you are matching on your paternal X as well as your maternal X
      Sisters will match also along the entire length of X due to having the identical X from father (half base pair matching, yellow)


      • #4
        Thank you!


        • #5

          Ok. I looked at the X one-to-one match. This is what I see:

          Chr Start Location End Location Centimorgans(cM) SNPs
          X 2,321 154,886,292 194.8 15,841

          The full base pair matching (green)is shown on the top line - most of it is green, but some of it is yellow (in the middle part of the line is mostly where it is yellow).
          The dark blue - matching segments greater than 7 cM - is a solid "bottom" line.

          So, the yellow is where we both match on the paternal side?



          • #6
            Hello again,

            One further question.

            Since there are 3 of us sisters, would the X that we received from father (should be the same for all of us) be the area where we all match in yellow?

            It is interesting because our graph does not show the same areas of yellow.



            • #7
              For the graphics option on the GEDmatch web site, the color coding on the upper part of the bar is YELLOW for "half match". Half match means you match ONE copy of the chromosome (X chromosome, in this case) at that location. GREEN color coding means that you match BOTH copies of the chromosome at that location. So GREEN is a stronger match than YELLOW.

              So, 3 daughters of the same father will match AT LEAST
              YELLOW over the entire length of the X chromosome, because they each got the same X chromosome from their father.

              The same 3 daughters, if they also have the same mother, will have SOME sections in GREEN, because they match not only on the X they each got from their father, but also on some part of the X chromosome that they received from their mother. Because of recombination, each daughter will probably get a different combination of segments drawn from their mother's 2 X chromosomes, but there will be some overlap. (If you were not paying attention in biology class and have forgotten how recombination works, now's a good time to do some reading!)


              • #8
                The following may help you understand the yellow and green at gedmatch

                Chromosome browsers merge the maternal and paternal chromosome pairs into one. Benefit with gedmatch they show the sections of Half base pair and Full base pair matching (matching on one chromosome of the pair or both)

                On Gedmatch, depending on testing company, some test the PAR regions of X, they are located at the beginning and end of the X chromosomes. These are sections can undergo recombination in the father when X is passed onto daughter. These sections can swab segments with the Y Chromosome. Sisters may show as a non match along these sections (red)

                PAR Region explanations
                Attached Files
                Last edited by prairielad; 9 May 2017, 07:38 PM.


                • #9
                  Thank you to both of you for good and simple explanations!

                  I am understanding more and more!