Quick (and silly) Hardy Weinberg question

[knuckles]

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So Kaplan Biochem gives a simplified version of HW, which seems to work. I was just wondering if anyone seems to know of any situations which it doesn't work. I may be a math idiot, but I don't see the problem with it, nor do I see why First Aid wouldn't mention it.

It just assumes the dominant allele is ~1 so it's

1 + 2q + q2 = 1

q2 = prevalence
2q = carrier frequency
q = frequency of recessive allele


and for AD dominant disease:
2q = disease prevalence
q2 = homozygous recessive (more severe disease)

and for XLR:

q = prevalence of disease AND recessive allele frequency (only one needed)
q2 = disease prevalence in females
2q = prevalence of female carriers


Seems a lot easier than using p2. Or maybe everything I just posted is the exact same thing as whats in First Aid. If someone could clarify, that'd be great.

 

[vr123]

The formula you're using estimates p as 1 because in most cases the disease allele is very rare so the frequency of the normal allele is very close to 1. However, if you have a situation where the disease is very prevalent (greater than 1/100, by the Kaplan biochem notes definition), then you need to use the original Hardy-Weinberg formula where p = 1-q.

 

[512TA]

So Kaplan Biochem gives a simplified version of HW, which seems to work. I was just wondering if anyone seems to know of any situations which it doesn't work. I may be a math idiot, but I don't see the problem with it, nor do I see why First Aid wouldn't mention it.

It just assumes the dominant allele is ~1 so it's

1 + 2q + q2 = 1

q2 = prevalence
2q = carrier frequency
q = frequency of recessive allele


and for AD dominant disease:
2q = disease prevalence
q2 = homozygous recessive (more severe disease)

and for XLR:

q = prevalence of disease AND recessive allele frequency (only one needed)
q2 = disease prevalence in females
2q = prevalence of female carriers


Seems a lot easier than using p2. Or maybe everything I just posted is the exact same thing as whats in First Aid. If someone could clarify, that'd be great.

you have stated it in correct manner.
by the way if you follow kaplan lectures videos you will come across the lecturer saying that all what you need to know is that this equation is used for AR and you really do not need to bother about AD disorders.
i have personally not come across a situation where this equation does not work 1+2q+q2

 

[kryptik]

works most of the time except in some situations where they make up a hypothetical situations, then you have to use the whole formula