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X and Y question plus male patten (?) baldness & IQ

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  • X and Y question plus male patten (?) baldness & IQ

    1. Approximately how much DNA will a son inherit from his maternal grandfather?

    2. Will any of his Y chromosome come from his mother's male line - mother's father? If so how much (ball park figure)?

    3. Am I right in thinking he will just get the X from his mother? In which case does it follow that none of his maternal grandfather's 'characteristics' will be inherited?

    4. Is there truth that if his maternal grandfather went bald he will also likely go bald as the 'baldness gene' is usually passed on in this manner? If so what's a likely percentage chance - e.g. more than 50%?

    5. How much in terms of character, temperament and IQ do you think is directly attributable to our ancestors? Do you think such traits are largely fixed despite our best efforts? I know there is much debate (nature v nurture) but there are so many highly intelligent and informed people here on this forum & would be greatly interested in their take. They'll also be likely coming at things from the family history 'interest' angle as well as the scientific one which means that answers more interesting & poignant I think.

    Hope the above makes sense. Sorry a few questions there.

    Thanks.

  • #2
    The answer to number 2 is no. The y chromosome is passed down virtually unchanged(except for the accumulation of mutations) from father to son. It doesn't recombine with other dna like autosomal dna does.

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    • #3
      1. Approximately 25% from each grandparent.

      2. No. Y chromosome is passed, essentially unchanged, from father to son. No women in the Y line.

      3. He may inherit an X chromosome from his maternal grandfather. Since his mother is female and has two X chromosomes, she inherited one from her mother (son's maternal grandmother), and one from her father (son's maternal grandfather). There is then a 50% chance that the X he gets will be from his maternal grandfather, 50% chance it will be from his maternal grandmother. In reality, due to crossover during meiosis (when his mother is producing eggs), part of the X will actually be from each of his maternal grandparents.

      He will also inherit approx 25% of his autosomal DNA (chromosomes 1-22) from his maternal grandfather (as in answer 1).

      4. No idea.

      5. Character and temperament? Who knows. Anecdotally, my kids and grandkids are a little too much like me.
      IQ has been shown to have a genetic association, but there's no evidence that I've seen that it's the major contributor. It may be, but the evidence is just not there yet.

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      • #4
        Originally posted by Paperblank View Post
        1. Approximately how much DNA will a son inherit from his maternal grandfather?
        Statistically - autosomal: 25%; X: Some (depending on recombination); Y: 0%

        2. Will any of his Y chromosome come from his mother's male line - mother's father? If so how much (ball park figure)?
        No, none. All of it comes from his father and so on, etc.

        3. Am I right in thinking he will just get the X from his mother? In which case does it follow that none of his maternal grandfather's 'characteristics' will be inherited?
        He does get his his X from his mother only (but that is a combination of both her Xs). But one of her Xs is a combo of her mother's 2 Xs and the other is from her father - a combo his mother's 2 Xs. As such the grandson will get some of his maternal grandfather's X becuase it is passed on to his mother which then recombines with the X she got from her mother.

        4. Is there truth that if his maternal grandfather went bald he will also likely go bald as the 'baldness gene' is usually passed on in this manner? If so what's a likely percentage chance - e.g. more than 50%?
        My understanding is that there are a number of factors not just the one that is X-linked. The fact that one is X-linked does not necessitate baldness. My maternal grandfather started to go bald in his 20's and I am not balding at all and I am in 40's.

        5. How much in terms of character, temperament and IQ do you think is directly attributable to our ancestors? Do you think such traits are largely fixed despite our best efforts? I know there is much debate (nature v nurture) but there are so many highly intelligent and informed people here on this forum & would be greatly interested in their take. They'll also be likely coming at things from the family history 'interest' angle as well as the scientific one which means that answers more interesting & poignant I think.

        Hope the above makes sense. Sorry a few questions there.

        Thanks.
        As far as IQ I think it is highly genetic but I am not so sure exactly what or how many different traits are making this contribution. If I am not mistaken some research suggested that a 10 point gain is possible just on one's attitude at a given moment and the environment in which that person finds themsleves. Plus I am sure some social and developmental issues are involved, probably less than genes, but none the less always a factor.

        Wiki has some good info on both balding and IQ. Check it out.
        Last edited by JTR; 25 January 2013, 10:29 PM.

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        • #5
          Originally posted by JTR View Post
          Statistically - autosomal: 25%; X: None; Y: 100%


          You mistakenly answered question 1 by the original poster. He asked how much DNA a son will inherit from his maternal grandfather. Perhaps you mistook maternal for paternal.

          The correct answer is autosomal - about 25%, as an average; x - anywhere from none to 100%, in most cases about 50% (usually a woman passes on a recombined x - roughly 50% from her mother and 50% from her father, but in unusual cases she can pass on an unrecombined x from either her mother or father); Y - none, the son gets his y entirely from his paternal, not maternal, grandfather.

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          • #6
            I don't believe that a cell will successfully complete meiosis if there's no crossover in the X chromosome. The synaptonemal complex will not form and the cell will not divide.

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            • #7
              Originally posted by MMaddi View Post
              You mistakenly answered question 1 by the original poster. He asked how much DNA a son will inherit from his maternal grandfather. Perhaps you mistook maternal for paternal.

              The correct answer is autosomal - about 25%, as an average; x - anywhere from none to 100%, in most cases about 50% (usually a woman passes on a recombined x - roughly 50% from her mother and 50% from her father, but in unusual cases she can pass on an unrecombined x from either her mother or father); Y - none, the son gets his y entirely from his paternal, not maternal, grandfather.
              Yeah I noticed that after I posted it and before you saw the correction - Thanks!.

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              • #8
                It's my understanding that pattern baldness is a "sex-limited" trait (not sex-linked). The gene resposible for the trait is not found on the sex chromosomes but the condition usually affects only one sex. The presence of male sex hormone appears to trigger the gene. Both men and women can be carriers.

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