Hardy-Weinberg (Genotype) Calculator

Formula first

Overview

The Hardy-Weinberg genotype equation describes the expected distribution of genotypes in a population that is not evolving. It mathematically demonstrates how allele frequencies (p and q) relate to the frequencies of homozygous dominant (p²), heterozygous (2pq), and homozygous recessive (q²) individuals.

Symbols

Variables

p = Dom. Allele Freq, q = Rec. Allele Freq, $p^2$ = Homo Dom Freq, 2pq = Hetero Freq, $q^2$ = Homo Rec Freq

Apply it well

When To Use

When to use: Apply this equation when evaluating if a population is in genetic equilibrium or if evolutionary forces are at work. It assumes a large population, random mating, no mutation, no migration, and no natural selection.

Why it matters: It serves as a critical null hypothesis in evolutionary biology, allowing scientists to detect deviations that indicate evolution is occurring. This helps researchers identify which specific factors, like sexual selection or genetic drift, are influencing a species.

Avoid these traps

Common Mistakes

• Forgetting the 2pq term.
• Using percentages instead of decimals.
• Not checking that p + q = 1 before calculating.
• Applying to evolving populations (only valid when assumptions are met).

One free problem

Practice Problem

In a stable population where the frequency of the recessive allele (q) is 0.3, calculate the frequency of the homozygous dominant genotype (P).

Solve for: $P$

Hint: First determine the dominant allele frequency (p) using p + q = 1, then square it to find P.

The full worked solution stays in the interactive walkthrough.

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Related Formulas

References

Sources

1. Wikipedia: Hardy-Weinberg principle
2. Campbell Biology, 12th Edition
3. Campbell Biology by Urry, Cain, Wasserman, Minorsky, and Reece
4. Hardy-Weinberg principle Wikipedia article
5. OCR A-Level Biology A — Genetics, Evolution and Ecosystems