The Hardy-Weinberg Principle explains genetic equilibrium in populations. It shows when allele frequencies stay constant over generations. Moreover, it serves as a null model in population genetics.
Gregor Hardy and Wilhelm Weinberg independently described this principle in 1908. They proved that mating alone does not change allele frequencies. Therefore, evolution does not occur under certain strict conditions.
The principle rests on five key assumptions. First, the population must be infinitely large. Second, no migration occurs. Third, no mutations happen. Fourth, mating occurs randomly. Finally, no natural selection acts on the population.
Under these ideal conditions, allele frequencies remain stable. Genotype frequencies also stay constant after one generation of random mating.
The mathematical formula captures this balance clearly. For a gene with two alleles (p and q), p represents the frequency of the dominant allele. q stands for the recessive allele. Additionally, p + q always equals 1.
Genotype frequencies follow these simple equations:
- Homozygous dominant: p²
- Heterozygous: 2pq
- Homozygous recessive: q²
These three add up to 1 (p² + 2pq + q² = 1). Thus, the population reaches Hardy-Weinberg equilibrium in just one generation of random mating.
Scientists use this principle as a benchmark. They compare real populations to the expected frequencies. If observed numbers differ significantly, evolutionary forces must be at work.
Deviations reveal important processes. Migration, mutation, selection, genetic drift, or non-random mating cause changes. Therefore, the Hardy-Weinberg principle helps detect evolution in action.
This elegant model remains a cornerstone of modern genetics. It provides a clear baseline for studying how populations evolve over time.
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