The Hardy-Weinberg principle is a concept conceived in 1908 by G.H Hardy and Wilhelm Weinberg. It describes a situation in which allelic or genotypic frequencies that drive evolution do not change over time in a population, and therefore that population is not evolving. The concept is based on Gregor Mendel’s law of independent assortment, which states that alleles of a trait can be separated independently from each other and can lead to fluctuations in the frequency of alleles over time. With this fact known, Hardy and Weinberg developed a series of conditions that must be met in order to determine whether or not a population is evolving. This established baseline is very useful in the study of population genetics. The conditions that must be met are as follows:

1. There can be no differences in the survival and reproductive success of individuals in the population. If a certain genotype of individuals in a population have a better chance of survival than the others or if a homozygous recessive gene expresses for some deadly condition, then we know automatically that nature will select for the genotype most fit to its environment and evolution would then occur.

2. Populations must not be added to or subtracted from by migration. If one has a population they are studying and added or subtracted individuals, the frequency of the gene(s) in question being observed would immediately change because the proportion of alleles to individuals would be thrown off. Because evolution is defined as a change in allele frequency over time in a population, a change in frequency by the addition or subtraction of that genotype would count as a population evolving.

3. There can be no mutation occurring. Simply put, mutations are one of the ways populations can evolve. It should be of note to mention that mutation is not the biggest concern because population geneticists generally study populations in a much shorter timescale than it would take for mutations to accumulate. Still, none allowed.

4. The population must be large enough to prevent sampling errors. A sampling error occurs when not enough specimens in that population are being observed. If the population is too small, then those individuals have a much bigger impact on allele frequency than one would see in an actual population and any statistical data gained could not possibly reflect the population as a whole, leading to inaccurate data. A smaller population would also be more impacted by genetic drift, which is also a form of evolution.

5. Matings within the population must be at random and not chosen or planned. If individuals with known allele frequencies were chosen to mate, It would interfere with your results, so mating must happen without any regard to phenotype, as would be the case in nature. This doesn’t affect the overall genotype frequency but not the frequency of alleles (because of independent assortment).

This test can have big applications in population genetics.On top of determining whether or not a population is/has evolved, we can also use it to make predictions on what evolutionary factors are affecting a population, predict allele frequencies in a population, and use it to look for correlations between genotype frequency and allele frequency.

References

Biology: How life works (2nd ed.). (2017). In B. A. Berry Andrew, Biology: How life works (2nd ed.) (p. CH 21). McGraw-Hill, NY: W. H. Freeman. Retrieved from http://www.macmillanhighered.com/launchpad/morris2e/4909413#/ebook/item/MODULE_bsi__F4951CED__2971__4486__BC4F__E109B2EE87D4/bsi__2ED633B9__F1E8__4C6C__82AA__0633C0C9F474?mode=Preview&toc=syllabusfilter&readOnly=False&renderIn=fne