Ways of Change: Drift and Selection

Question 1

Explain the influence of population size on random genetic drift, including bottlenecks and founder effects.

Answer 1

Small populations tend to lose genetic diversity more quickly than large populations due to stochastic sampling error, even during short-term reductions such as bottlenecks and founder effects.

Question 2

Explain how the concept of natural selection relates to relative fitness.

Answer 2

When a genotype produces an expression or phenotype that allows an organism to survive and ultimately reproduce, thus contributing to the genetic composition of the future generation, they have high fitness. Comparatively, they have a higher relative fitness if they can contribute more of their genetic information to the future generation. This will be the case for individuals whose phenotypic expression provides them with a selective advantage to overcome environmental selective pressures.

Question 3

Describe how gene flow (migration) affects allele frequencies.

Answer 3

Gene flow introduces more genetic variation.

Question 4

What are the four processes that drive evolution?

Answer 4

• Natural Selection (increases the frequency of alleles that contribute to reproductive success in a particular environment)
• Genetic drift (causes allele frequencies to change randomly)
• Gene flow (occurs when individuals leave one population, join antoher, and breed)
• Mutation (modifies allele frequencies by continually introducing new alleles)

Question 5

Heardy-Weinberg Equilibrium as the Null Hypothesis

Answer 5

Suggests that there is no relationship between two measured phenomena. Imagined that all of the alles from all gametes in each generation go into a single group called a gene pool and then combine randomly.

Question 6

Hardy-Weinberg Allele Frequency Equation

Answer 6

p + q = 1

Question 7

Hardy-Weinberg Genotype Frequency Equation

Answer 7

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

Question 8

The Hardy-Weinberg Equilibrium Assumptions

Answer 8

1. Population is infinitely large (No genetic drift)
2. Genotypes do not confer differences in fitness (No natural selection - all individuals contribute equally to the gene pool)
3. There is no mutation (no new alleles are intriduced into the gene pool)
4. Mating is random (no mate choice; gametes cobine randomly)
5. There is no migration (No gene flow — no new alleles are added or lost from the gene pool)

Question 9

Hardy–Weinberg equilibrium occurs when
A. the frequency of alleles in a population changes as
expected, given the effects of selection.
B. the frequency of alleles in a population does not
change across generations.
C. the change in the frequency of alleles matches the
environmental conditions.
D. the number of genes on a chromosome remains
the same over time.

Answer 9

B. The frequency of alleles in a population does not change across generations.

Question 10

What would the ending frequency of the pand qalleles
be if the assumptions of Hardy–Weinberg are met, and
their initial frequency is 60:40?
A. The resulting frequency should be 50:50.
B. The resulting frequency should be 60:40.
C. The resulting frequency should be 100:0, in favor of
pbecause of its selective advantage.
D. The resulting frequency should be 0:100 in favor of
qbecause of its selective advantage.

Answer 10

B. The resulting frequency should be 60:40.

Question 11

What is the result when the assumptions of the Hardy–
Weinberg equilibrium are not met?
A. No change occurs in allele frequencies.
B. The mutation rates increase.
C. The population evolves.
D. The population dies off.

Answer 11

C. The population evolves.

Question 12

Define Genetic Drift

Answer 12

Genetic drift is evolution due to random increases or decreases in alleles in a population from one generation to the next. The effects of drift are stronger in small populations than in large populations.

Question 13

Define Genetic Bottleneck

Answer 13

a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as specicide, widespread violence or intentional culling, and human population planning.

Question 14

Define Founder effects

Answer 14

When a small number of individuals leave a population and colonize a new, isolated habitat.

Question 15

How will the genotypes of individuals in a founding population compare to those of individuals from the source population?
A. It depends on the size of their genome.
B. There will be reduced variation in alleles.
C. There will be increased variation in alleles.
D. Genotypes are unaffected by founder effects.

Answer 15

B. There will be reduced variation in alleles.

Question 16

What two factors determine how fast an allele is lost because of a bottleneck?
A. how rapidly the bottleneck occurs and birth rate
B. mutation rate and average time to sexual maturity
C. average age of individuals and size of the genome
D. population size and starting frequency of the allele

Answer 16

D. Population size and starting frequency of the allele.

Question 17

Define Relative Fitness

Answer 17

Relative fitness of a genotype describes the success of that genotype at producing new individuals standardized by the success of other genotypes in the population.