USMLE Forums banner

Calculating the "P" in Hardy-Weinberg Equation

4K views 13 replies 7 participants last post by  DocSikorski 
#1 ·
here is question about PKU relating to following equation

p2 + 2pq + q2 = 1

prevalence of PKU is 1 in 10,000 live births
WHAT IS CARRIER FREQUENCY
here

q2= 1/10,000
we want to calculate 2pq

q= 1/100 =0.01
HOW WE CAN CALCULATE p??
prof says p would be 1-q
how p would be 1-q following above equation?
 
#12 ·
The way I remember this for the exam is: The carrier frequency = 2 x the square root of the prevalence of the disease.

The assumption that this makes (and is generally true) is that the prevalence of the non-diseased approximates 1.

That is why 2pq is generally just 2 p since the q can be dropped as it approximates 1.
 
#14 ·
If q is 1/1,000,000 or whatever than p is 999,999/1,000,000 no matter how low is q, bare in mind that p is always 1-q. So carrier frequency will be 2x(1-q)xq you can choose the closest answer option to your value. Practice this and then when u see the logic u can assume the p is 1 or very close to it when q is extremely low.

But in cas of CF let's say in Norway, q will be around 1/5...
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top