BiologyPopulation GeneticsA-Level

Hardy-Weinberg Principle Calculator

The Hardy-Weinberg Principle provides a mathematical model to calculate allele and genotype frequencies in a stable, non-evolving population.

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Frequency of recessive allele

Formula first

Overview

Under ideal conditions including random mating and no mutation, migration, or natural selection, allele frequencies remain constant across generations. The equation + 2pq + = 1 represents the distribution of genotypes in a population, where homozygous dominant, heterozygous, and homozygous recessive frequencies are summed to unity. This model serves as a null hypothesis to detect evolutionary change in biological systems.

Symbols

Variables

p = Frequency of dominant allele, q = Frequency of recessive allele, = Frequency of homozygous dominant genotype, 2pq = Frequency of heterozygous genotype, = Frequency of homozygous recessive genotype

Frequency of dominant allele
Variable
Frequency of recessive allele
Variable
Frequency of homozygous dominant genotype
Variable
2pq
Frequency of heterozygous genotype
Variable
Frequency of homozygous recessive genotype
Variable

Apply it well

When To Use

When to use: Use this when you are given data on phenotypic frequencies (usually the recessive phenotype) in a population and need to calculate the allele frequency or the frequency of carriers.

Why it matters: It allows biologists to quantify the rate of evolution and identify which evolutionary pressures, such as natural selection or genetic drift, are acting upon a population.

Avoid these traps

Common Mistakes

  • Confusing the frequency of the homozygous recessive phenotype () with the frequency of the recessive allele (q).
  • Assuming a population is in Hardy-Weinberg equilibrium when it is undergoing natural selection or significant mutation.

One free problem

Practice Problem

In a population where 16% of individuals exhibit the recessive phenotype, what is the frequency of the recessive allele (q)?

qSquared0.16

Solve for:

Hint: The frequency of the recessive phenotype represents . You must take the square root to find q.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Hardy, G. H. (1908). Mendelian proportions in a mixed population.
  2. Campbell Biology, 12th Edition.
  3. AQA/OCR/Edexcel A-Level Biology Specification