| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: use the chi-squared test to test the significance of differences between observed and expected results (the formula for the chi-squared test will be provided, as shown in the Mathematical requirements) |
Learning Objective/s:
- Describe why a statistical test is required when comparing observed and expected phenotypic ratios.
- Apply the chi‑squared formula to calculate the test statistic from given data.
- Interpret the chi‑squared result to accept or reject the Mendelian ratio hypothesis.
- Evaluate possible biological explanations for a significant deviation.
|
Materials Needed:
- Projector or interactive whiteboard
- Printed worksheet with observed data tables
- Calculator or spreadsheet software
- Chi‑squared distribution table (digital or paper)
- Sample dataset (e.g., pea seed counts)
- Whiteboard markers
|
Introduction:
Begin with a quick recall of Mendelian 3:1 ratios from a monohybrid cross. Highlight that real experimental counts rarely match the exact ratio because of random variation. Explain that today’s success criteria are to calculate a chi‑squared value and decide whether the data support the expected ratio.
|
Lesson Structure:
- Do‑now (5'): Students write the expected 3:1 ratio for a Rr × Rr cross and note why observed numbers may differ.
- Mini‑lecture (10'): Introduce the chi‑squared test, present the formula, null hypothesis, and degrees of freedom.
- Guided example (15'): Walk through the provided pea‑seed example, calculating expected counts, chi‑squared statistic, and comparing to the critical value.
- Pair activity (15'): Each pair receives a new dataset, computes the chi‑squared value, determines significance, and records a brief interpretation.
- Whole‑class discussion (10'): Groups share results; discuss biological reasons for significant vs. non‑significant outcomes.
- Exit ticket (5'): Write one sentence stating what the chi‑squared result reveals about the gene’s inheritance pattern.
|
Conclusion:
Summarize how the chi‑squared test quantifies the match between observed data and Mendelian expectations. Collect exit tickets to gauge understanding, and assign homework: students must analyse a provided dataset and prepare a short paragraph explaining their conclusion and any biological factors that could affect the result.
|