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#1
05-24-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610
Genetics Question from DIT

What is the frequency of the Aa genotype and the AA genotype if the frequency of allele A is 0.9% ?

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My answers were Aa = 0.18 and AA = 0.81.

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DIT answers were Aa = 0.095 and AA = 0.9

Can someone explain ?

#2
05-24-2012
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DIT is wrong?
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 The above post was thanked by: Hope2Pass (05-25-2012)
#3
05-24-2012
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Going back to the basic equation=

A^2 + 2Aa + a^2= 1

The 0.9 that DIT gave is the frequency of AA already. They basically gave you A^2 from the original equation. Now you have to square root that:
AA= 0.9
A= 0.95

A+a= 1
a= 1-0.95
a= 0.05

2Aa= which is the frequency of the genotype= 2(0.95)(0.05)= 0.095

Hope that helped.

Last edited by islandcrazy; 05-24-2012 at 08:55 PM. Reason: forgot a word :P
 The above post was thanked by: Hope2Pass (05-25-2012)

#4
05-24-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,353 Threads: 94 Thanked 877 Times in 507 Posts Reputation: 890

I'd say .18 and .81 too. But this will be for a regular AR inheritance.

For x-linked recessive frequency of allele is equal to heterozygous males or something like that... I think here DIT could have talked about that example precisely
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 The above post was thanked by: Hope2Pass (05-25-2012)
#5
05-25-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610

But the question is exactly as stated above =

"What is the frequency of the Aa genotype and the AA genotype if the frequency of allele A is 0.9% ?"

By saying that frequency of allele A = 0.9% ... doesn't that mean that p = 0.9 ?!

Quote:
 Originally Posted by islandcrazy The 0.9 that DIT gave is the frequency of AA already. They basically gave you A^2 from the original equation.
How would you assume that allele A means the genotype AA Or Am I misreading something here ? lol
#6
05-25-2012
 USMLE Forums Addict Steps History: Not yet Posts: 177 Threads: 25 Thanked 75 Times in 55 Posts Reputation: 87

What section was this in DIT, I think I wrote down some information on how to solve it, but I can't find it.
#7
05-25-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610

Quote:
 Originally Posted by islandcrazy What section was this in DIT, I think I wrote down some information on how to solve it, but I can't find it.
It was in the work book under genetics ... Its in the genetics end session quiz.
Btw your explanation is right. That's how he got the answer but I just don't know how the frequency for Allele A becomes the frequency for genotype AA!
#8
05-25-2012
 USMLE Forums Addict Steps History: 1 + CS Posts: 160 Threads: 6 Thanked 47 Times in 38 Posts Reputation: 57

Quote:
 Originally Posted by Hope2Pass It was in the work book under genetics ... Its in the genetics end session quiz. Btw your explanation is right. That's how he got the answer but I just don't know how the frequency for Allele A becomes the frequency for genotype AA!
ok,
This is how I always interpret....
if question gives you that the frequency of some allele , here A in this much PERCENTAGE, than I always assume that thet have given A*A...
then work it out and get our a and then 2Aa...

Hope that helped....
you can try this out in practice question...bt dont get too bogged down buddy...
click, smile..and...move on..
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#9
05-25-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 647 Times in 409 Posts Reputation: 657

i remember this exact question because he pulled random numbers out of his ass

he misread the question, used numbers that werent in the question and hence got a different answer.

both him and you are correct, because you both did different questions.

sometimes he skips questions or misreads them when taking up quizes. its not often but you'll notice it when it happens. this is one such case.
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 The above post was thanked by: DocSikorski (05-25-2012)

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