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#1




NBME 12 question
Ok, I came across this HARDYWEINBERG question in the 3rd section, where they ask you to figure out the carrier risk.
Man, I cant figure it out! I calculate the answer, but its not in the options list. They have an incidence of CF in the general population to be 1/40,000 so i take a square root of it and get 1/200 trying to find the carrier rate (2pq) I have 2 x 199/200 x 1/200 I get 0.0095 as a result! Do they mean that this is kinda close to 1/100 or what? I have trouble with HardyWeinberg.
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#2




you are correct till 2pq = 200 ....... but have to take p as 1 so q = 1/100

#3




Quote:
(p+q=1) ?
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#4




I know but its given in kaplan biochem ..... dont remember much but had noted down that to calculate carriers need to take p as 1 becoz p are normal people and are very large part of the population and q is a very small part so they approximate it .something like that dont know the exact detail ... just need to cram this up for solving them it i felt .....

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#5




NBME form 12 block 3 #20
With these type of questions...I suggest that you write down what's given as you're reading the question
 autosomal recessive  incidence of cystic fibrosis in the population: (1)/(40,000)  what's the wife's risk for being a carrier? this type of question is called "carrier prevalence" &/or "disease prevalence" in this case, they are asking for carrier prevalence = "wife's risk" this is the equation that you need to use for this type of question is called "carrier prevalence" or "disease prevalence" 2 + 2q + q^2 2q = carrier prevalence q^2 = disease prevalence they gave you disease prevalence in the question = incidence of cystic fibrosis in the population = q^2 = (1)/(40,000) take the square root of [(1)/(40,000)] = 1/200 = q what's the wife's risk for being a carrier? they want use to find "carrier prevalence" "carrier prevalence" = 2q = (2)[1/200] = 1/100 ans. 1/100 
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#6




Quote:
But why do u take p as 1?
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#7




I think it's becoz value of P >>> q and it reaches approximately 1. So for simplicity p=1 is used.

#8




Quote:
So I guess In this case .0095 is rounded to .01 = 1/100...
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#9




In that case, Yes you can't take p=1 becoz prevalence of the disease is very high vs in the question where it is very low. In any case, I would do it the old fashioned way. It's less complicated. lol

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DocSikorski (03212012) 
Tags 
BiostatisticsEpidemiology, NBME 
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