Hardy–Weinberg Equilibrium, explained.
Hardy–Weinberg proportions p², 2pq and q² describe genotype frequencies after random union of gametes under the model's assumptions.
Why it happens
A slider sets allele A frequency p. Random-mating mode shows AA=p², Aa=2p(1−p), aa=(1−p)². All-homozygote mode shows AA=p, Aa=0, aa=1−p. Both have the same allele frequency, despite different genotype proportions.
Hardy–Weinberg proportions p², 2pq and q² describe genotype frequencies after random union of gametes under the model's assumptions.
Read the result
Track the allele-frequency statistic while switching genotype constructions. Identical allele frequencies do not imply identical heterozygosity.
A worked example
The same alleles in different pairings
Set A frequency to fifty percent. Random mating gives twenty-five percent AA, fifty percent Aa and twenty-five percent aa.
Switch to all homozygotes: fifty percent AA, zero percent Aa and fifty percent aa.
Both constructions retain fifty percent A alleles. Pairing has changed without changing the allele total.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
A slider sets allele A frequency p. Random-mating mode shows AA=p², Aa=2p(1−p), aa=(1−p)². All-homozygote mode shows AA=p, Aa=0, aa=1−p. Both have the same allele frequency, despite different genotype proportions.
Where this idea is useful
A practical use
A genetic survey can compare observed genotype frequencies with a random-mating reference before investigating possible departures.
A common misconception
“Hardy–Weinberg means every population has equal genotype frequencies.”
The proportions depend on allele frequency and model assumptions. Equal thirds are not the default, and departures have multiple possible causes.
What this explanation leaves out
- These are expected proportions, not exact finite-population counts or evidence of a particular evolutionary mechanism. Equilibrium across generations additionally excludes selection, mutation, migration and drift.
Does a departure prove natural selection?
No. Nonrandom mating, population structure, measurement error, sampling and other mechanisms can also create departures from the reference proportions.
Are you comparing allele counts, genotype proportions, or a claim about stability across generations?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.