Population Genetics and Evolutionary Change
Alleles in Populations
Hardy-Weinberg Principle
The Hardy-Weinberg model describes a non-evolving population with allele frequencies and , where and genotype frequencies follow .
Conditions for Equilibrium
Hardy-Weinberg equilibrium assumes random mating, large population size, no mutation, no migration, and no natural selection.
Why the Model Matters
Hardy-Weinberg is a null model. Deviations from it suggest evolutionary forces such as selection, drift, gene flow, or nonrandom mating.
If and , what is the expected heterozygote frequency?
The heterozygote frequency is .
Correct answer: 0.42
What does it mean if a population deviates from Hardy-Weinberg equilibrium?
Deviations indicate that the population is not behaving as a null model.
Correct answer: At least one Hardy-Weinberg assumption is violated, suggesting evolutionary change or nonrandom mating.
Microevolutionary Forces
Natural selection changes genotype frequencies by differential reproductive success. Genetic drift causes random changes, especially in small populations. Gene flow introduces alleles through migration, and mutation creates new variants.
Which force is strongest in very small populations?
Random sampling effects are amplified in small populations.
Correct answer: Genetic drift
What is the relationship between selection and fitness?
Fitness is central to evolutionary change.
Correct answer: Selection acts on heritable differences that affect fitness, which is reproductive success.
Applications
Population genetics is used in conservation biology, medicine, agriculture, and ancestry inference. It helps estimate carrier frequencies and predict how traits change over time.