AP Biology Unit 7 Topic 2: Population genetics

What to Know

Allele frequencies describe genetic makeup at the population level.
Hardy-Weinberg expectations provide a comparison point for detecting evolutionary change.
Small populations are especially affected by chance events such as drift.
Always connect this topic back to the larger unit: Natural Selection.

Detailed Notes

Population genetics belongs to Unit 7: Natural Selection. Population genetics studies how allele frequencies change through selection, chance, migration, mutation, and mating patterns. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Allele frequencies describe genetic makeup at the population level. Hardy-Weinberg expectations provide a comparison point for detecting evolutionary change. Small populations are especially affected by chance events such as drift.

Model to use: Use allele-frequency data or Hardy-Weinberg equations to compare observed and expected genotype frequencies. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: When data differ from equilibrium expectations, identify which condition may be violated and justify it with the scenario. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Allele frequency

The proportion of a specific allele in a population's gene pool.

Genetic drift

Random change in allele frequencies, especially in small populations.

Gene flow

Movement of alleles between populations through migration and reproduction.

Hardy-Weinberg equilibrium

A model describing genotype frequencies when a population is not evolving under specific assumptions.

Bottleneck effect

Genetic drift after a population is sharply reduced in size.

Founder effect

Genetic drift when a new population starts from a small number of individuals.

Quick Practice

How would you explain Population genetics in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

Biology concept reference: Biology for AP Courses by OpenStax, Rice University. Access for free at OpenStax. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. EduCompanion used this source as a conceptual reference and rewrote the study notes in original wording.