Hardy–Weinberg equilibrium: a baseline for evolution — Biology, 14–17
Hardy–Weinberg equilibrium describes a population in which allele frequencies stay constant because no evolutionary force is changing them. It gives biologists a baseline against which real populations can be compared.
A population that does not evolve
Imagine an ideal population with random mating, no mutation, no migration, no natural selection and a very large size. In that special case, the proportions of alleles and genotypes remain stable from one generation to the next. This is a reference model, not a claim that real populations are perfect.
Why use an impossible model?
A baseline makes change visible. If a real population differs from the expected Hardy–Weinberg proportions, at least one assumption may be failing: selection, migration, mutation, chance effects or non-random mating. The model does not explain every cause, but it tells you where to look.
Calculating expected genotypes
Suppose allele A has frequency p = 0.6, so allele a has q = 0.4. The expected genotype frequencies are AA = p² = 0.36, Aa = 2pq = 0.48 and aa = q² = 0.16. In 1,000 individuals, that predicts 360 AA, 480 Aa and 160 aa.
Not an evolution law
You might think the equations predict what every population must look like. That is a reasonable mistake because the numbers seem exact, but they are conditional predictions. If the observed counts differ, the result is evidence that an assumption is not met, not proof that the calculation is wrong.
A tool for population studies
Biologists use the model to compare allele and genotype data from real populations. For example, a medical survey can estimate whether a recessive condition is more common than expected, while conservation scientists can look for signs of inbreeding or recent migration. The model guides questions; it does not replace evidence.
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