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Title: Pedigree Probability Question - Autosomal Dominant Post by: Zoneator on Sep 20, 2014 Hi everyone,
I need help with this question: A woman whose father was diagnosed with the dominant Huntington Disease (HD) marries a man whose family has no history of the disease. The woman does not know if she carries the trait and she is pregnant with the couple's first child. What is the probability that the child will develop HD? The answer is .25, but I keep getting .375 instead! My reasoning is that the father of married woman could either be HH or Hh (50% probability of either one). If HH, then the woman will definitely by Hh, so her child will have a 50% chance of having HD. If the father is Hh, then the woman has a 50% chance of being Hh, and thus her child will have a 25% chance of having HD. Since the father could be HH or Hh, I did (50% + 25%)/ 2 = 37.5% or 3/8 is the probability of the child could develop HD. Can someone explain my flawed reasoning? Thank you so much Title: Re: Pedigree Probability Question - Autosomal Dominant Post by: padre on Sep 20, 2014 It might be useful to draw a pedigree, then use product rule to combine probability of the woman carrying the HD allele with the probability that she will pass it on to her child. Remember, HD is a dominant disease.
The answer is 1/4. |