13. How Populations Evolve

PTC is a chemical that elicits a bitter taste response in some people. The ability to taste PTC depends on the presence of the PTC-tasting allele. Individuals with at least one copy of the PTC-tasting allele taste PTC as bitter. It is estimated that about 70% of the population taste PTC. Assuming that the population is in Hardy-Weinberg equilibrium for this trait, what percent of the population would you expect to be heterozygous for this trait?

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

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?

Jorge and Claire are given the following data on fur density in red pandas at zoos in the United States. Is the following population in Hardy-Weinberg equilibrium?

160 homozygous for the F allele, 137 heterozygotes, and 29 homozygous for the f allele.

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?

In a population of glass frogs (Hyalinobatrachium munozorum) you collect 200 individuals. Of those, you determine that 160 are homozygous for the H allele, 10 are homozygous for the h allele, and 30 are heterozygous. Is this population in Hardy-Weinberg equilibrium? If not, why not?

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.