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Homework Help: Likelihood of inheriting autosomal dominant diseases

  1. Jun 27, 2012 #1


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    This IS wrong. This only holds true if one of your parents is HETEROZYGOUS dominant.

    Hh x hh => 50% chance of offspring having Huntington's disease.

    However, if one of your parents is HOMOZYGOUS DOMINANT ..

    HH x hh => 100% chance of offspring having Huntington's diseases.

    Simple Punnett squares will verify the above.

    Therefore, the probability should be 75% if one parent has Huntington's disease. Am I right?
  2. jcsd
  3. Jun 27, 2012 #2


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    I don't know what you are quoting or context, but I'd guess this is an approximation based on homozygous being rare in the population.

    The dynamics of Huntingdon's is a bit more complex than just the inheritance of a stable chromosome, and was explained in a recent thread on PF.
  4. Jun 28, 2012 #3


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    You are making the faulty assumption that heterozygotes and homozygotes are equally abundant. In reality, the probability is 0.5p+(1-p), where p is the proportion of Huntington's patients who are heterozygous for the disease allele. As mentioned by epenguin, the disease allele is rare, so there are many more heterozygotes than homozygotes, and p~1.
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