angeldr
Forum Newbie
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hi friends..
can anyone please tell me how to calculate prevalence if carrier rate is given...? and "hardy-weinberg equation"? with example if possible..
kind of confuse...!! thanks
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| angeldr
Forum Newbie
Topics: 5
Posts: 15
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no one ??? so sad !!!!!!
is anyone here... to ans this little que?
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| Tiff
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Found this from another site. Hope it helps.
Calculation of prevalence of genetic dz given the carrier state: eg cystic fibrosis
1. if carrier rate of CF is 1/25, the prevalence is calculated as follows:
2. number of couples at risk - is equal to the carrier rate in males x carrier rate in females, or 1/25 x 1/25 = 1/625 couples at risk.
3. risk of having child with CF (AR dz) - 1/4, hence 1/625 x 1/4 = prevalence of 1/2500
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| angeldr
Forum Newbie
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thanks tiff
i got this. but can u plz tell me how we count carrier rate when prevalence is given.? specially while calculating couples at risk it says for example in this case 2500/4.. how ?? anyidea?
that confuses me.
thanks again :-)
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| Tiff
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This is where Hardy Weinberg is important. The equation in p2 + 2pq + q2. (Remember p + q = 1).
So if the prevalence is given like in this case, 1/2500, then you have to take the square root q2 which is 1/50 to use the calculation. To reiterate, the value for prevalence is given as 1/2500 which means that 1/2500 represents the recessive component (q2). This is why you need to take the square root of 1/2500 which equals 1/50.
So... if q = 1/50 then p has to equal 49/50 (because remember p+q = 1)
Now you can use that equation p2 + 2pq + q2.
(2pq) represents the carrier rate. You know what q is already. You've also figured out what p should be.
So... 2 x (49/50) x (1/50) = carrier rate = 0.04 or 4% or 1/25.
To add to this...if 1/25 is the carrier rate that represents heterozygous individuals...lets use "C" for cystic fibrosis. 1/25 represents Cc individuals. Therefore calculating the couples at risk is multiplying female carrier rate to male carrier rate. 1/25 x 1/25 = 1/625
Much of this is knowing how to back calculate when needed. You'll come full circle when you calculate the prevalence by multiplying the carrier rate (1/25) by couples at risk (1/625) which equals 1/2500.
Hope this helps.
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| angeldr
Forum Newbie
Topics: 5
Posts: 15
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hi tiff
how are you today?
thanks so so very much. that was clear cut answer and it pierced all the way to my neurons. haha.
i shall try to catch u if i will find my self stuck in calculation stuff.
thanks again and wish u a good luck !
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