# Hardy–Weinberg Principle

Hardy–Weinberg Principle or the Hardy–Weinberg equilibrium model or law states that the allele and genotype frequencies in a population will remain constant from generation to generation in the absence of any other evolutionary factors. These influences or impacts include mutation, mate choice, selection, genetic drift, meiotic drive and gene flow. The Hardy–Weinberg equation is a unique mathematical calculation that can be used to evaluate the genetic variation of a population at the equilibrium.

In 1908, G. H. Hardy, an English mathematician and Wilhelm Weinberg, a German physician independently described a basic principle effective in population genetics widely known as the Hardy-Weinberg principle. The principle is crucial concept in population genetics and it helps predict how gene frequencies will inherited from one generation to another within a given set of assumptions.

The Hardy–Weinberg principle is clear in the sense that, it clarifies that a large randomly breeding population allele frequencies will remain the same from generation to generation considering that there is no gene migration, mutation or genetic drift influences. This principle is imperative because it gives biologist a standard from which to measure changes in allele frequency in a population.

In order to make any helpful assumptions on the Hardy–Weinberg principle, it is wise to reorganize that it is a neutral equilibrium meaning that a population disturbed from its Hardy–Weinberg genotype frequencies will have to reach equilibrium after a single generation of random mating; however, it will be a new equilibrium if allele frequencies are altered. This characteristic helps distinguish a neutral equilibrium from a stable equilibrium in which a disrupted system returns to the same equilibrium state. There are certain occurrences when the Hardy–Weinberg principle or law fails to apply. This effect can be attributed to a number of factors and they include;

• Mutation– Here, the frequency of the gene B and its allele b will not remain in Hardy–Weinberg equilibrium if the rate if mutation of B -> b changes.
• Gene flow-   Many species are made up of local populations whose members breed within the group. Each of these local populations can develop a gene pool unique from that of the other local population. On the other hand, some members of one of the population may breed with occasional immigrants from adjacent population of the same species. This leads to a new flow of genes frequencies in the populations.
• Genetic drift- Interbreeding is usually limited to the members of the residents. If the population is small, Hardy–Weinberg principle may be disturbed. This may eliminate certain number of the populace.  Then frequency of an allele may begin to drift towards higher or lower values. Genetic drift will lead to evolutionary change, but it is not adaptive.
• Other issues that will make the Hardy–Weinberg law fail are nonrandom mating and natural selection.

The above-mentioned factors affect changes in allele frequencies and when subjected to more forces, the population of choice will disrupt the Hardy–Weinberg assumptions and evolution will take place. The Hardy–Weinberg principle thus constitutes a null model for the field of population genetics and it is helpful to the study of evolution.

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### References

http://www.nature.com/scitable/knowledge/library/the-hardy-weinberg-principle-13235724

http://www.nfstc.org/pdi/Subject07/pdi_s07_m01_02.htm

http://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_principle