Evolution Exam 2

Module 5: Hardy-Weinberg & Population Genetics

📌 Concept: Hardy-Weinberg as a Null Model
Q: Why is the Hardy-Weinberg model considered a null model?
A: It provides a baseline expectation for allele and genotype frequencies in a population that is not evolving. Deviations indicate evolutionary forces at play.

📌 Concept: Evolution in Population Genetics
Q: How is evolution defined from a population genetics perspective?
A: Evolution is the change in allele or genotype frequencies in a population over time.

📌 Concept: Hardy-Weinberg Assumptions
Q: What five conditions must be met for Hardy-Weinberg equilibrium?
A:

1. No mutation

2. No natural selection

3. No gene flow (migration)

4. Random mating

5. Large population size (no genetic drift)

📌 Concept: Detecting Evolutionary Forces
Q: What does it mean if a population is not in Hardy-Weinberg equilibrium?
A: It means one or more evolutionary forces (mutation, selection, genetic drift, non-random mating, or migration) are affecting allele frequencies.

📌 Concept: Hardy-Weinberg Calculations
Q: Given allele frequencies B = 0.1 and b = 0.9, what are the expected genotype frequencies?
A:
Using p2+2pq+q2=1p^2 + 2pq + q^2 = 1p2+2pq+q2=1:

• BB=0.12=0.01BB = 0.1^2 = 0.01BB=0.12=0.01

• Bb=2(0.1)(0.9)=0.18Bb = 2(0.1)(0.9) = 0.18Bb=2(0.1)(0.9)=0.18

• bb=0.92=0.81bb = 0.9^2 = 0.81bb=0.92=0.81

Module 6: Mutation & Selection

📌 Concept: Causes of Evolutionary Change
Q: What factors cause deviations from Hardy-Weinberg equilibrium?
A: Mutation, natural selection, genetic drift, gene flow (migration), and non-random mating.

📌 Concept: Mutation-Selection Balance
Q: What is mutation-selection balance?
A: It is the equilibrium where new mutations arise at the same rate that selection removes them.

📌 Concept: Mutation as a Source of Variation
Q: Why is mutation considered the raw material for evolution?
A: It introduces genetic variation, which is necessary for natural selection and adaptation.

📌 Concept: Effects of Selection on Allele Frequencies
Q: How do different types of selection affect allele frequencies?

• Directional selection: One allele is favored, leading to fixation.

• Overdominance (heterozygote advantage): Heterozygotes have the highest fitness, maintaining genetic diversity.

• Underdominance (heterozygote disadvantage): Heterozygotes have the lowest fitness, leading to allele loss.

📌 Concept: Real-World Example of Selection
Q: How has selection influenced rock pocket mice populations?
A: Mice with dark fur are favored in lava-covered environments, demonstrating directional selection due to predation pressure.

Module 7: Non-Random Mating, Migration, & Genetic Drift

📌 Concept: Assortative Mating
Q: How does positive assortative mating affect genotypic frequencies?
A: Increases homozygosity and decreases heterozygosity.

Q: How does negative assortative mating affect genotypic frequencies?
A: Increases heterozygosity by favoring mating between genetically different individuals.

📌 Concept: Inbreeding & Conservation Concerns
Q: How is inbreeding related to positive assortative mating?
A: Inbreeding is a type of positive assortative mating where individuals mate with relatives, increasing the risk of recessive disorders.

Q: Why is inbreeding depression a conservation concern?
A: It reduces genetic diversity, leading to lower fitness, increased disease susceptibility, and a higher risk of extinction.

📌 Concept: Migration & Gene Flow
Q: How does migration affect genetic variation?
A:

• Within a population: Increases genetic diversity.

• Between populations: Can homogenize allele frequencies over time.

📌 Concept: Migration Models
Q: Explain the continent-island model of migration.
A: A large population (continent) continually supplies alleles to a smaller population (island), gradually shifting allele frequencies on the island.

Q: Explain the island model of migration.
A: Migration occurs between multiple small populations, leading to shared allele frequencies across islands.

📌 Concept: Genetic Drift & Small Populations
Q: How does genetic drift affect allele frequencies?
A: It causes random changes, potentially leading to allele fixation or loss, especially in small populations.

📌 Concept: Founder Effect & Bottleneck
Q: How are the founder effect and bottleneck effect related to genetic drift?
A: Both involve small population sizes, leading to random shifts in allele frequencies:

• Founder effect: A few individuals establish a new population with limited genetic variation.

• Bottleneck effect: A population undergoes a drastic reduction in size, losing genetic diversity.

📌 Concept: Genetic Drift vs. Natural Selection
Q: How is genetic drift different from natural selection?
A:

• Genetic drift: Random changes in allele frequencies due to chance.

• Natural selection: Non-random changes where beneficial alleles increase in frequency.

📌 Concept: Real-World Examples
Q: Give an example of genetic drift in a real-world population.
A: The cheetah population experienced a genetic bottleneck, leading to low genetic diversity.

Q: Give an example of natural selection in action.
A: Peppered moths changed in frequency based on pollution levels affecting tree bark color.