| Lesson Plan |
| Grade: Year 12 |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: explain how selection, the founder effect and genetic drift, including the bottleneck effect, may affect allele frequencies in populations |
Learning Objective/s:
- Describe how natural and artificial selection change allele frequencies using fitness differentials.
- Explain the founder and bottleneck effects as forms of genetic drift and their impact on genetic variation.
- Compare deterministic (selection) and stochastic (drift) forces in altering population genetics.
- Apply the Hardy‑Weinberg framework to predict allele‑frequency changes after a given evolutionary force.
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Materials Needed:
- Projector and screen
- Whiteboard and markers
- Student handouts with allele‑frequency tables
- Interactive simulation software (e.g., PopG) on computers
- Colored beads or counters for a physical drift activity
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Introduction:
Begin with a quick poll: “If you could choose any trait for a crop, what would it be and why?” This connects to students’ prior knowledge of breeding and sets the stage for discussing how selection shapes populations. Today’s success criteria are to identify the mechanisms of selection, founder, and bottleneck effects and predict their influence on allele frequencies.
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Lesson Structure:
- Do‑now (5 min): Students complete a short worksheet calculating allele frequencies from a simple genotype table.
- Mini‑lecture (10 min): Review Hardy‑Weinberg equilibrium and introduce the selection equation with real‑world examples.
- Guided practice (12 min): Work in pairs to model natural selection using fitness values on the board; calculate new p′.
- Interactive simulation (10 min): Use the computer program to compare artificial selection versus drift in small vs large populations.
- Hands‑on activity (8 min): “Bead drift” – students randomly draw beads to simulate founder and bottleneck effects and record resulting frequencies.
- Think‑pair‑share (5 min): Discuss how each force would affect genetic variation in a conservation scenario.
- Formative check (5 min): Exit ticket – one sentence describing which force would most likely cause rapid allele loss in a tiny population.
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Conclusion:
Summarise that selection drives predictable changes while drift introduces randomness, especially after founder or bottleneck events. Ask students to write an exit ticket summarising one key difference between selection and drift. For homework, assign a short problem set calculating allele‑frequency shifts under different evolutionary forces.
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