13. How Populations Evolve

In the Hardy-Weinberg equation, what does the term 2pq represent?

Which of the following statements about the Hardy-Weinberg equation are true?

I) For a gene with two alleles, q² represents the frequency of one of the homozygotes.

II) If p and q both equal 0.5, you expect 50% of the population to be heterozygous.

III) The p² and q² terms will be equal as they both represent the probability of being a homozygote.

Imagine a population of cats where one gene codes for eye color. The E allele codes for yellow eyes and is dominant. The e allele codes for green eyes and is recessive. The frequency of the E allele is 0.6, and the frequency of the e allele is 0.4. Assuming the population is in Hardy-Weinberg equilibrium, what percent of the population will have green eyes?

Sickle cell anemia is a recessive trait. In Nigeria, it is estimated that 2.4% of the population is born with sickle cell anemia. Heterozygotes for the sickle cell allele are said to have the sickle cell trait and have few sickle cell symptoms. Assuming that the population is in Hardy Weinberg equilibrium for the sickle cell gene, what percentage of the population would you expect to have the sickle cell trait?