Chapter 20.3 - Evolution and the Hardy-Weinberg Equilibrium

Question 1

Textbook: What gives us a snapshot of the pattern of genetic variation in a population?

Answer 1

Allele frequencies

Question 2

Textbook: What is evolution?

Answer 2

Evolution is a change in allele or genotype frequency from one generation to the next (over time).

Question 3

Textbook: Do populations or individuals evolve?

Answer 3

Populations do.
Populations evolve as gene frequencies change.

Question 4

Textbook: What describes situations in which allele and genotype frequencies do not change?

Answer 4

The Hardy-Weinberg Equilibrium

Question 5

Textbook: What are the conditions for the Hardy-Weinberg Equilibrium to work?

Answer 5

1. There is no difference in the survival and reproductive success of individuals with different genotypes.
2. The population is sufficiently large to prevent sampling errors.
3. Populations are not added to or subtracted from by migration.
4. There is no mutation.
5. Individuals mate at random

Question 6

Textbook: What does the Hardy-Weinberg Equilibrium predict?

Answer 6

The Hardy-Weinberg equilibrium predicts the expected genotype frequencies from allele frequencies (as long as the Hardy-Weinberg conditions are met).

Question 7

Textbook: When we find a population whose allele or genotype frequencies are not in Hardy-Weinberg equilibrium, what can we infer about the population?

Answer 7

We can infer that evolution has occurred in that population.

Question 8

Textbook: What are the primary mechanisms of evolution?

Answer 8

Natural selection, mutation, genetic drift, nonrandom mating, and gene flow.

Question 9

Textbook: Can evolution occur without allele frequency changes? If not, why not? If so, how?

Answer 9

Yes. Evolution is a change within a population over time in the frequency of alleles or genotypes; the frequency of a genotype can change without the frequency of the alleles changing.

Question 10

Textbook: What can and can’t we conclude about a population whose allele frequencies are not in Hardy-Weinberg equilibrium?

Answer 10

We can conclude that the population is evolving.
We cannot tell what mechanism is causing the population to evolve.

Question 11

Textbook: How would you calculate the genotype frequencies of a population in Hardy-Weinberg equilibrium, given the allele frequencies for that trait?

Answer 11

You can use known allele frequencies to determine genotype frequencies in that population using the Hardy-Weinberg equation:
(p² + 2pq + q² = 1).
p represents the allele frequency of one allele and q represents the other. The frequency of homozygous dominant individuals is determined by calculating p², the frequency of homozygous recessive individuals is determined by calculating q², and the frequency of heterozygous individuals is determined by calculating 2pq.

Question 12

Lectures: Why is it difficult to see evolution occurring?

Answer 12

Because for many species, evolution happens over the course of many thousands of years.

Question 13

Lectures: Why did Darwin argue that evidence of extinction supports the theory of evolution?

Answer 13

It shows that the number and types of species have changed over time.

Question 14

Lectures: Researchers have found fossils of a horse species in Colorado. If deeper rock deposits contain smaller species, and more recent deposits contain larger species, what does this tell us about evolution?

Answer 14

It provides evidence that species change over time.

Question 15

Lectures: In a hypothetical population of 1000 frogs there exists a gene with two alleles. 280 of the frogs are homozygous dominant (DD), and 220 are homozygous recessive (dd). What is the frequency of the D allele in the population?

Answer 15

280 DD frogs
1000 total frogs

p² = 280/1000 = 0.28

p = 0.53
p = 53%