mineralwater

Hey everyone,

This is the question:

"Two spaceships land on Planet Zork. One holds 50 people from an entirely brown-eyed population. The other carries 50 from a Hardy-Weinberg population in which there is eye colour variation. 32 of the passengers have brown eyes and 8 blue. The blue eyed allele, b, is obviously recessive to brown, B.

What is the frequency of the alleles B and b on the planet immediately after the landing?"

That's the exam question. First of all, I'm going to assume that there is an error in the question, because 8 + 32 =/= 50. I'm going to change it to 18 blue eyed people. And I correct in assuming this is a typo?

Calculating the frequency of the b allele is simple; because b is recessive to B, the 18 individuals who have blue eyes must be homozygous for b at the eye colour locus. Because each of the blue-eyed individuals has 2 copies of the b allele, and because the total number of people on the planet is 50 + 50 = 100, the frequency of b homozygotes must be 2(18) / 100 = 36 / 100 = 0.36.

The 2 HW equations:

p + q = 1

p^2 + 2pq + q^2 = 1

We have just calculated the frequency of bb homozygotes in the HW population. This is represented in the equations as q^2. So q^2 is 0.36.

We can use this to calculate q = [sqrt]q^2 = [sqrt]0.36 = 0.6.

So q = 0.6, which represents the frequency of b.

If we know the frequency of b, we can calculate the frequency of B in the HW population by using p + q = 1.

p = 1 - q

= 1 - 0.6

= 0.4.

So the frequency of B in the HW population is 0.4.

There is no eye colour variation in the entirely brown-eyed population. So I am going to assume that they are all BB homozygotes. Am I correct in making this assumption?

The frequency of B in the entirely brown-eyed population must then come to 1.

The overall frequency of B must therefore be (1 + 0.4) / 2 = 0.7

The overall frequency of b must be (0 + 0.6) / 2 = 0.3.

So I have calculated the overall frequencies of alleles b and B to be 0.3 and 0.7 respectively.

Are there any mistakes in my methodology/final answer?

Is there a simpler method to calculator this?

Many thanks in advance.