# Confused about allele frequency question....?

The problem is that there's a population of 20 people. These people became isolated for many years. Out of these initial 20 people, two of them were heterozygous carrier for a horrible disease. If the frequency of the allele didn't change, what's the incidence of the horrible disease?

I'm not sure what it is.

Here are the possible answers:

A. The population born with cystic fibrosis will be 0.50%.

B. The population born with cystic fibrosis will be 0.25%.

C. The population born with cystic fibrosis will be 0.0025%.

D. The population born with cystic fibrosis will be 2.50%.

### 1 Answer

- JazSincLv 79 months agoFavorite Answer
You have 20 people. You have 40 alleles.

Of those 40 alleles, two are defective.

freq(q) = 2/40 = 0.05

Your teacher then wants you to plug that into the Hardy-Weinberg equilbrium equations to come up with

freq(qq) = q^2 = 0.05 * 0.05 = 0.0025 = 0.25%

and so you would choose this from your multiple choices:

B. The population born with cystic fibrosis will be 0.25%.

Why this is bogus: You were told that this was a HORRIBLE DISEASE. The frequency of the bad allele would decrease over time due to selection.

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