Polygenic Trait Distribution Visualizer
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About This MicroSim
This visualization demonstrates how polygenic inheritance produces continuous phenotype distributions. As the number of contributing genes increases from 1 to 6, the histogram transitions from a discrete 1:2:1 Mendelian ratio to an approximately normal (bell-shaped) curve. The binomial coefficients that generate each distribution are shown in the "Show Math" panel.
How to Use
- Drag the slider to change the number of contributing genes (1-6).
- Hover over any bar to see its exact frequency percentage.
- Normal Curve button overlays a theoretical normal distribution for comparison (visible at 2+ genes).
- Show Math button displays the binomial expansion, coefficients, and exact frequencies.
- Observe the summary statistics (classes, mean, SD, shape) below the chart.
Lesson Plan
Grade Level
9-12 (college placement Biology)
Duration
10-15 minutes
Prerequisites
- Understanding of Mendelian single-gene inheritance (1:2:1 ratio for incomplete dominance)
- Concept of additive alleles contributing equally to a quantitative trait
Activities
- Exploration (5 min): Start at 1 gene and observe the familiar 1:2:1 ratio. Slowly increase to 6 genes and watch the distribution become bell-shaped. Toggle the normal curve overlay to see how well the distribution matches.
- Guided Practice (5 min): Use "Show Math" to examine the binomial coefficients. Answer: "How many phenotypic classes exist for 3 genes? For 5 genes?" Verify with the slider.
- Assessment (5 min): Explain in writing why human height follows a bell curve distribution. How many genes would need to contribute for the distribution to appear continuous?
Assessment
- Can students explain why more genes produce more phenotypic classes?
- Can students connect the binomial expansion to the shape of the distribution?
- Can students distinguish polygenic inheritance from single-gene Mendelian patterns?