Dmd

[BrisketAttack]

Uworld question:

Incidence of DMD is 1/3000 males. what is gene frequency of this x-linked mutation? answer: 1/3000

I read thru uworld's explanation and I still don't understand why this is. can anyone enlighten me?

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[The Angriest Bird]

From top of my head

1/3000 x 1/3 = 1/9000

"1/3" is the factor you use for x-link diseases i think, because 1 out of 3 x chromosomes is carried by male (1 in male, 2 in female)

But I think the TRICK is that the 1/3000 probability is in MALES, not in the general population. So, 1 out of 1 x chromosome is carried in the males in the male population. Therefore it's

1/3000 x 1 = 1/3000

This is truly a tricky question. I wouldn't get it right either if you didn't show me the answer. We all know UW is bad-ass hard sometimes.

 

[TerpMD]

Bc DMD is XLR, that means that all men who have the gene are going to show the trait. (So freq of allele=freq of disease in men) So the frequency of the allele in men is =q (1/3000). If they were asking you the prevalence of DISEASE in women it would be q^2, but he frequency of the ALLELE in the population is the same for both.
Hope this helps.

 

[Doctor J]

Frequency of allele in males = prevalence in males due to reasons offered above... q = 1/3000, p = 2999/3000

Frequency of allele in females = 1/3000. This is because (while this may be seen as circular reasoning, it's true) the prevalence in males is 1/3000. So few females present with DMD (q^2 = 1/9,000,000) that you can ignore that population.

THUS, the total frequency of the allele = 1/3000.

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