anne
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A 30-year-old man has a sister who died from infantile Tay-Sachs disease, an autosomal recessive disorder that is lethal by age 6. What is the probability that this man is a heterozygous carrier, and, if 1% of individuals in the general population are heterozygous carriers, what is the probability that this man will produce an affected offspring if he mates with a member of the general population?
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| asmi
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0.0025
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| anne
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1st part of the question=the person may have 2/3 rd chance of being a carrier of the disease if we consider that his parents were both heterozygous for the disease(as is commonly seen).
2nd part---chances of his child being affected by the disease if he happens to be carrier(considering his wife a carrier too)=2/3x1/100x.25=0.0017
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| asmi
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anne,
How did you know 2/3 chance of being a carrier ?
Its 25 % right (for AR diseases)
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| anne
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as its an AR condition,and we suppose(as in most cases)that his parents would both be carriers,the person has 1/4th chance of being affected,and 3/4th chance of being unaffected.if the person is unaffected,he has 1/3rd chance of being homozygous normal,and 2/3rd chance of being a carrier.
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| usmleasr
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good q 
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| bobby
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can you please explain how you calculated che chance of the woman being heterozygote, since the offspring will only be affected if the man mates with a heterozygote female.
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| anne
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as 1% of the individuals in the population are heterozygous,we calculate it by guessing that the woman may be a carrier.
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| asmi
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thanks anne
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| bobby
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i will like to know one think. i thought the hardy weiberg rule would have been applied. had it been the prevalence of the heterozygote was 10% or 5%, would we have assumed that the lady is eterozygote?
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| oddissy4u
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i still didnt get the calculation part ...plz explain ...
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