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Hardy-Weinberg Equilibrium Calculator

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About This MicroSim

This interactive calculator lets students input observed genotype counts for a two-allele system (AA, Aa, aa) and immediately see the calculated allele frequencies (\(p\) and \(q\)), expected genotype frequencies under Hardy-Weinberg equilibrium (\(p^2\), \(2pq\), \(q^2\)), a bar chart comparing observed vs. expected frequencies, and a chi-square goodness-of-fit test with a clear verdict on whether the population is in equilibrium. Three preset examples demonstrate populations in HWE, under selection, and experiencing drift.

How to Use

  1. Click an input field (AA, Aa, or aa) and type the observed number of individuals with that genotype.
  2. Watch the calculations update — allele frequencies (\(p\), \(q\)), expected values, bar chart, and chi-square test all recalculate instantly.
  3. Compare the bar chart — solid blue bars are observed frequencies; dashed red outlines are HWE expected frequencies.
  4. Read the chi-square result — green means the population is in equilibrium; red means it deviates from HWE.
  5. Click preset buttons ("In HWE", "Selection", "Drift") to load example populations.
  6. Use Tab to move between input fields, Enter to deselect.

Lesson Plan

Grade Level

9-12 (college placement Biology)

Duration

10-15 minutes

Prerequisites

  • Understanding of allele frequency concepts (\(p\) and \(q\))
  • Knowledge of the Hardy-Weinberg equations (\(p^2 + 2pq + q^2 = 1\))
  • Familiarity with the five conditions for HWE (no selection, no mutation, no migration, large population, random mating)

Activities

  1. Exploration (5 min): Load each of the three presets. For each one, note: Is the population in HWE? How do the observed and expected bars compare? What might explain the deviation?
  2. Guided Practice (5 min): Enter a population with AA=160, Aa=480, aa=360 (N=1000). Calculate \(p\) and \(q\) by hand first, then check against the calculator. Predict whether this population is in HWE before looking at the chi-square result.
  3. Assessment (5 min): Design a population of 500 individuals that would NOT be in HWE. Enter your counts and verify. Then adjust the counts until the population IS in equilibrium. What pattern do the counts follow?

Assessment

  • Can students calculate \(p\) and \(q\) from genotype counts?
  • Can students apply the Hardy-Weinberg equation to predict expected genotype frequencies?
  • Can students interpret a chi-square test result to determine if a population is in equilibrium?
  • Can students identify which HWE condition is likely violated when a population deviates from equilibrium?

References

  1. Hardy-Weinberg principle - Wikipedia
  2. Chi-squared test - Wikipedia
  3. Allele frequency - Wikipedia