Hardy-Weinberg Equilibrium: Principles and Applications
The Hardy-Weinberg principle states that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary influences.
The equation: p² + 2pq + q² = 1, where p = frequency of dominant allele, q = frequency of recessive allele, p² = homozygous dominant, 2pq = heterozygous, q² = homozygous recessive.
Example: If 4% of a population has a recessive disorder (q² = 0.04), then q = 0.20, p = 0.80. Carriers (2pq) = 2 × 0.80 × 0.20 = 0.32 = 32% of the population.
Five conditions for HWE: 1) No mutations, 2) No migration, 3) No natural selection, 4) Random mating, 5) Large population. If any is violated, the population is evolving.
To test if a population is in HWE, use the Chi-square test: χ² = Σ(observed - expected)² / expected. If χ² < 3.84 (df=1, p=0.05), the population is in equilibrium.
Use our Hardy-Weinberg and Allele Frequency calculators in the Molecular Genetics category to practice with real population data.