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Nondisjunction in Meiosis Visualizer

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About This MicroSim

This step-through visualization compares three parallel columns showing the same cell progressing through meiosis: normal meiosis (left), nondisjunction in meiosis I (center), and nondisjunction in meiosis II (right). Students can pinpoint exactly where each error occurs and trace the chromosomal consequences through both divisions to the final gametes.

How to Use

  1. Click "Next" to advance through the 5 stages of meiosis (synchronized across all three columns).
  2. Compare columns at each stage — the error step is highlighted with a red glow and "FAIL" label.
  3. Read descriptions at the bottom of each column for stage-specific explanations.
  4. At the final stage, observe the gamete compositions: green borders = normal (n=2), red borders = abnormal (n+1 or n-1).
  5. Use "Previous" to step back and re-examine any stage.

Lesson Plan

Grade Level

9-12 (college placement Biology)

Duration

10-15 minutes

Prerequisites

  • Understanding of meiosis I (homolog separation) and meiosis II (sister chromatid separation)
  • Knowledge of diploid (2n) and haploid (n) chromosome numbers
  • Familiarity with homologous chromosomes vs. sister chromatids

Activities

  1. Exploration (5 min): Step through all 5 stages. At each stage, compare the three columns. Identify which column shows the error and at which stage.
  2. Guided Practice (5 min): Answer: "How do the final gametes differ between nondisjunction in meiosis I vs. meiosis II?" Note the number of abnormal gametes in each case.
  3. Assessment (5 min): Predict: if a gamete with n+1 chromosomes is fertilized by a normal gamete, what will the resulting zygote's chromosome number be? What condition does this cause?

Assessment

  • Can students identify at which meiotic stage each type of nondisjunction occurs?
  • Can students predict the chromosomal composition of gametes resulting from each error?
  • Can students explain why nondisjunction in meiosis I produces 4 abnormal gametes but nondisjunction in meiosis II produces only 2 abnormal gametes?

References

  1. Nondisjunction - Wikipedia
  2. Aneuploidy - Wikipedia
  3. Down syndrome - Wikipedia