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AP Course

AP Biology

Updated for the AP Biology framework effective fall 2025, with concept lessons, data reasoning, quizzes, and practice problems.

Explore life from molecules and cells to evolution and ecosystems through the official AP Biology unit sequence.

Lessons
Structure of Water and Hydrogen BondingElements of LifeIntroduction to MacromoleculesCarbohydratesLipidsNucleic AcidsProteinsCell Structure and FunctionCell SizePlasma MembraneMembrane PermeabilityMembrane TransportFacilitated DiffusionTonicity and OsmoregulationMechanisms of TransportCell CompartmentalizationOrigins of Cell CompartmentalizationEnzymesEnvironmental Impacts on Enzyme FunctionCellular EnergyPhotosynthesisCellular RespirationCell CommunicationIntroduction to Signal TransductionSignal Transduction PathwaysFeedbackCell CycleRegulation of Cell CycleMeiosisMeiosis and Genetic DiversityMendelian GeneticsNon-Mendelian GeneticsEnvironmental Effects on PhenotypeDNA and RNA StructureDNA ReplicationTranscription and RNA ProcessingTranslationRegulation of Gene ExpressionGene Expression and Cell SpecializationMutationsBiotechnologyIntroduction to Natural SelectionNatural SelectionArtificial SelectionPopulation GeneticsHardy–Weinberg EquilibriumEvidence of EvolutionCommon AncestryContinuing EvolutionPhylogenySpeciationVariations in PopulationsOrigins of Life on EarthResponses to the EnvironmentEnergy Flow Through EcosystemsPopulation EcologyEffect of Density on PopulationsCommunity EcologyBiodiversityDisruptions in Ecosystems
Quizzes
Practice Problems Lab design, data analysis, and FRQ practice resources can be added here.

AP Biology · Unit 7 · Topic 7.1

Introduction to Natural Selection

Evolution is a population-level change explained with variation, inheritance, selection, drift, and common ancestry evidence.

1. Topic Lens

Introduction to Natural Selection is studied through natural selection. Connect the system boundary, interacting parts, and measurable evidence before applying a formula.

\[p^2+2pq+q^2=1\]

2. Why the Formula Works

The relationship is built from definitions and conservation reasoning:

  1. For two alleles, their frequencies sum to one: p+q=1.
  2. Random union of gametes is modeled by multiplying the binomial by itself.
  3. Expanding gives expected genotype frequencies under Hardy-Weinberg assumptions.
\[p+q=1\Rightarrow(p+q)^2=p^2+2pq+q^2\]

3. Detailed Visual Model

Pixel diagram for Introduction to Natural SelectionOriginal schematic connecting Introduction to Natural Selection to Natural Selection.
Introduction to Natural Selection: an original pixel-style model. Use it as a schematic, not a literal scale drawing.

4. Worked Example and Lab Link

A recessive phenotype has frequency q²=0.09 in an idealized population. Find q, p, and 2pq.

Answer: q=0.30, p=0.70, and the expected heterozygote frequency is 0.42.

Investigation idea: Simulate allele sampling across small and large populations to separate drift from directional selection.

Common trap: Hardy-Weinberg is a null model; matching its equation does not prove that every assumption is perfectly met.

Checkpoint · Topic 7.1

Explain how introduction to natural selection supports or limits this conclusion: q=0.30, p=0.70, and the expected heterozygote frequency is 0.42.

Official curriculum reference: College Board AP Biology course page. The explanation and worked example are independently written for this study site.