| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: interpret and construct genetic diagrams, including Punnett squares, to explain and predict the results of test crosses |
Learning Objective/s:
- Describe the relationship between genes, alleles, genotypes and phenotypes.
- Explain how dominance, incomplete dominance and codominance affect inheritance patterns.
- Construct monohybrid and dihybrid Punnett squares to determine genotype and phenotype ratios.
- Apply test‑cross methodology to infer unknown genotypes.
- Use the Hardy–Weinberg equation to predict allele frequencies in a population.
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Materials Needed:
- Projector or interactive whiteboard
- Printed worksheets with Punnett‑square grids
- Coloured tokens or cards representing alleles
- PowerPoint slides showing example crosses
- Graph paper and calculators
- Access to an online genetics simulation (optional)
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Introduction:
Begin with a quick think‑pair‑share: “If two tall pea plants produce a short offspring, what might be happening genetically?” Connect this to prior learning about alleles and dominance, and tell students they will learn to visualise such scenarios using Punnett squares. Success will be demonstrated by correctly constructing a Punnett square and interpreting the resulting ratios.
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Lesson Structure:
- Do‑now (5’) – short quiz on genotype vs. phenotype.
- Mini‑lecture (10’) – review genes, alleles, and dominance relationships with slides.
- Guided practice (15’) – teacher models a monohybrid Punnett square (AA × aa); students replicate on worksheet.
- Collaborative activity (15’) – groups build a dihybrid Punnett square (RrYy × RrYy) using tokens and discuss ratios.
- Test‑cross demonstration (10’) – walk through procedure; students predict outcomes for an unknown dominant parent.
- Quick check (5’) – exit ticket: one sentence describing the steps to determine an unknown genotype via a test cross.
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Conclusion:
Summarise how Punnett squares translate parental genotypes into expected offspring ratios and how test crosses reveal hidden genotypes. For the exit ticket, students write the key steps they would follow in a test cross. Assign homework: complete the worksheet with two additional monohybrid crosses and one dihybrid cross.
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