Hardy-Weinberg equilibrium is a concept that suggests that allele frequency won't change over generations in a population as long as no evolutionary forces are acting on the population. If there is random mating and no selective forces, then both genotype and allele frequency will remain the same over generations [1]

The Hardy-Weinberg equation calculates genetic variation of a population at equilibrium and it looks like:

p2 + 2pq + q2 = 1

Where "p" is the frequency of the A allele and "q" is the frequency of the a allele. In the equation, p2 represents the genotype AA, q2 represents the genotype aa, and 2pq represents the heterozygous genotype Aa. The frequency must of all alleles must equal 1 for the equation to hold true.[2]


The X-axis shows allele frequency for p and q and the Y-axis shows the genotype frequencies. Each line represents one of the three possible genotypes. By Johnuniq (Own work) via Wikimedia Commons[3]

This principle rarely happens because it requires a set of seven assumptions that are unlikely to happen in nature. These assumptions are: [4]

1) Organisms are diploid

2) Only sexual reproduction occurs (no asexual reproduction)

3) Generations are not overlapping

4) All mating is totally random

5) Population size is infinitely large

6) Allele frequencies are equal in all sexes

7) There is no migration, mutation, or selection

Although the Hardy-Weinberg Equilibrium theory would provide scientists with a clear and effective way to identify allele frequencies, it almost never happens in nature and, more often than not, fails to apply. There are many violations of the Hardy-Weinberg principle, including but not limited to: non-random mating, genetic drift, natural selection, and mutation. [5]These violations of the principle result in deviations from the expected, and therefore causing the principle to be invalid. Although the population may still experience Hardy-Weinberg equilibrium for a generation, the following generations will experience a shift in allele frequencies.[4]

Reference List

1) Hardy-Weinberg equilibrium. 2014. Scitable by Nature Education. Retrieved from

2) Hardy-Weinberg equation. 2014. Scitable by Nature Education. Retrieved from

3) Johnuniq (Own work) [CC BY-SA 3.0 (

4) Hardy-Weinberg principle. n.d. In Wikipedia. Retrieved 16 March 2015 from

5) The Hardy-Weinberg equilibrium. 2014. Kimball's Biology Pages. Retrieved from

Cite error: <ref> tags exist, but no <references/> tag was found