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#1
07-17-2014
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 148 Threads: 37 Thanked 73 Times in 57 Posts Reputation: 83
Hardyweinberg equilibrium: reg 2pq??

Incase if prevalence of the disease q square is less than 1/100..and suppose if we have to calculate carrier frequency 2pq for autosomal recessive disease....do we have to calculate p as p=1-q or can we take p is approximately equal to 1?Some questions in kaplan Qbank follow this rule but some questions dont..so its confusing.. can someone help??

#2
07-17-2014
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 107 Threads: 18 Thanked 71 Times in 26 Posts Reputation: 81

For the calculation of HWE you need to subtract 1-q to obtain p.
Only in cases where the disease is rare (less than 1 in 10000) the root of q will be very small and 1-q~1 i.e. frequency of mutated allele is very low.
In your example, a population frequency of 1% for an autosomal recessive disease means an allele frequency of about 10% (root of 0.01 is 0.1) and has a large impact on the frequency of the normal allele. So, yes, do the subtraction in this case.
 The above post was thanked by: hope2015 (07-17-2014)

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