Question

HWE Question

Based on the objective you should feel comfortable calculating expected genotype frequencies when given observed allele frequencies. You should also be able to compare expected genotype frequencies from HWE to observed frequencies and determine if evolution is occurring.

Here's a sample problem. You can do this without a calculator!

Let's take the noob gene, a gene with two known alleles that determines feather color in the eastern lark. The two alleles, let's call them delta and gamma, can be sequenced. In fact, looking at a population in southern GA, you discover that 60% of the alleles in the population are the delta allele.

So question 1, what is the percentage of the gamma allele in the population?

Even more interesting, based on HWE what is the expected frequency of the population that is homozygous gamma? (as well as homozygous delta or heterozygous)

Now, after surveying an isolated population of eastern larks, you find that 20% of the population is homozygous gama (gamma gamma), 65% heterozygous (gamma delta) and 10% homozygous delta (delta delta) and 5% of the population is a previously undescribed genotype - zeta zeta (homozygous zeta).

What can you conclude about evolution in the population and why? If evolution is occurring, which mechanism(s) would be responsible (and which ones can you cross off your list).

Answer 1

The frequency of delta allele is 60% or 0.6.

The frequency of gamma allele is 40% or 0.4.

Q1. The expected frequency of population that is homozygous gamma is (0.4 * 0.4) = 0.16.

The expected frequency of population that is homozygous delta is 0.6 * 0.6 = 0.36.

The expected frequency of heterozygous population is 2 * 0.6 * 0.4 = 0.48.

The evolution occurred due to mutations. There is a decrease in frequency of homogygous delta population. The mutation occurred in the delta gene which gave rise to a new allele zeta.