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Noobie With A Question On Sibling DNA?

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  • Noobie With A Question On Sibling DNA?

    Hi,
    My sister and I had our DNA tests done recently and results showed us sharing 36.3% Shared DNA....Does that constitute Full or Half Sibling as there might be a question on that subject? Thanks..Excaliber954

  • #2
    Full siblings share roughly 50% of their DNA in common, Half siblings share roughly 25%, and ¾ siblings share roughly 37.5%.

    Therefore I'd bet that you are ¾ siblings, which would be something like if your mother had two children sired by two brothers, or in other words, if your mother had an affair with your uncle (father's brother).
    Last edited by Dabney Carr; 24 February 2017, 11:15 PM.

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    • #3
      What do you share on the X chromosome?

      Sisters with the same father will show approximately 196cM on X (not fool proof as each could have received the same X from mother, her maternal and paternal X's may not have recombined)

      It is also rare that brothers will inherit the same X from their mother, therefore if you are 3/4 siblings due to fathers being brothers, it is unlikely that you will share the entire X chromosomes also.

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      • #4
        Which company did you test with, and is that where the 36% estimate is from?

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        • #5
          prairielad - Approximately, how many cMs would a female share with her paternal aunt on the X? Thanks!

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          • #6
            FTDNA doesn't give you "extra credit" for fully identical regions. Your number is typical for full siblings with FTDNA's method (37.5%)

            http://isogg.org/wiki/Autosomal_DNA_statistics#Table

            If you upload your raw data to GEDmatch, I'd expect you to see fully identical regions in a one-to-one comparison there.

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            • #7
              Originally posted by marietta View Post
              prairielad - Approximately, how many cMs would a female share with her paternal aunt on the X? Thanks!
              I don't think there is a set number, it would be the same average that a brother/sister share on their maternal X, as fathers X is passed on intact to their daughters.

              Could be anywhere from 0 to 196cM

              My Sisters share 153cM with paternal Aunt, longest block 54cM.

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