Evolution Exam 2

Why is the Hardy-Weinberg model considered a null model?

It provides a baseline expectation for allele and genotype frequencies in a population that is not evolving. Deviations indicate evolutionary forces at play.

How is evolution defined from a population genetics perspective?

Evolution is the change in allele or genotype frequencies in a population over time.

What five conditions must be met for Hardy-Weinberg equilibrium?

No mutation, No natural selection, No gene flow (migration), Random mating, Large population size (no genetic drift).

What does it mean if a population is not in Hardy-Weinberg equilibrium?

It means one or more evolutionary forces are affecting allele frequencies.

Given allele frequencies B = 0.1 and b = 0.9, what are the expected genotype frequencies?

BB = 0.01, Bb = 0.18, bb = 0.81.

What factors cause deviations from Hardy-Weinberg equilibrium?

Mutation, natural selection, genetic drift, gene flow (migration), and non-random mating.

What is mutation-selection balance?

Equilibrium where new mutations arise at the same rate that selection removes them.

Why is mutation considered the raw material for evolution?

Introduces genetic variation necessary for natural selection and adaptation.

Frequency-independent Selections

Directional, Stabilizing, Disruptive, Overdominance, Underdominance

Frequency Dependent Selections

Positive frequency and Negative frequency

How has selection influenced rock pocket mice populations?

Mice with dark fur are favored in lava-covered environments, showing directional selection due to predation pressure.

Positive assortative mating effect on genotypic frequencies?

Increases homozygosity and decreases heterozygosity.

Negative assortative mating effect on genotypic frequencies?

Increases heterozygosity, favoring mating between genetically different individuals.

Inbreeding relation to positive assortative mating?

Inbreeding is a type of positive assortative mating where individuals mate with relatives.

Why is inbreeding depression a conservation concern?

Reduces genetic diversity, leading to lower fitness and increased disease susceptibility.

How does migration affect genetic variation?

Within a population: Increases genetic diversity; Between populations: Can homogenize allele frequencies over time.

Explain the continent-island model of migration.

A large population (continent) supplies alleles to a smaller population (island), island allele frequencies converge to continent allele frequencies.

Explain the island model of migration.

Migration occurs between multiple small populations, leading to convergence on mean of all islands allele frequencies.

How does genetic drift affect allele frequencies?

Causes random changes, potentially leading to allele fixation or loss, especially in small populations.

How are the founder effect and bottleneck effect related to genetic drift?

Both involve small population sizes, leading to random shifts in allele frequencies.

How is genetic drift different from natural selection?

Genetic drift involves random changes in allele frequencies, while natural selection involves non-random changes where beneficial alleles increase in frequency.

Example of genetic drift in a real-world population.

The cheetah population experienced a genetic bottleneck, leading to low genetic diversity.

Give an example of natural selection in action.

Peppered moths changed in frequency based on pollution levels affecting tree bark color.

Three ingredients for Natural Selection

Variation, trait heritability, selective reproductive success

Directional Selection

One allele is favored, leading to allele fixation (one replaces all)

Stabilizing Selection

Intermediate phenotypes are more fit than extreme ones, less diversity

Disruptive Selection

Two or more extreme phenotypes more fit than intermediate; more diversity

Overdominance Selection

heterozygote advantage; higher fitness

Underdominance Selection

heterozygote disadvantage; lower fitness

Positive Frequency Dependent Selection

phenotype fitness increases as more common

Negative Frequency Dependent Selection

phenotype fitness decreases as more common