Hardy-Weinberg’s principles, also referred to as Hardy-Weinberg equilibrium or law, explains that the frequencies of alleles as well as genotype in a given population is constant from generation-to-generation given that evolutionary frequencies are absent. Some of the evolutionary influences include mutation, genetic-drift, mate-choice and also meiotic-drive (Salanti, Amountza, Ntzani, & Ioannidis, 2005). In order to determine the allele frequencies, Hardy-Weinberg law can be explained using two equations.
( p+q ) 2 =1
Therefore ; p 2 +2pq+q 2 =1
Where; p = the dominant allele frequency
q =the recessive allele frequency
using binomial expansion, the three terms can be explained as;
p 2 = homozygous dominance frequency (AA)
2 pq = heterozygous frequency (Aa)
q 2 =homozygous recessive frequency (aa)
for any given population to be at a genetic equilibrium, p+q=1.0 where by the sum of the dominant and recessive frequencies of alleles is at 100% (Waples, 2014).
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An example of an instance whereby the allele frequencies is not constant therefore leading to a situation where a population is not at equilibrium is as follows.
The Punnet squire above follows a single gene with dial alleles, (A) and (a) allele. In the Punnet Squire, the frequencies of alleles are represented as ‘ p’ and ‘ q’ . As stated by Hardy-Weinberg’s law, these alleles will remain constant assuming that there are no external influences to the population. This means that, p+q=1.0 (Waples, 2014).
A hypothetical situation whereby a population of butterflies with only dual alleles for a particular gene that codes for their unique colors. A single allele codes for green color (C g ) while the other allele codes for color blue (C b ). In the above hypothetical scenario, assuming that part of the heterozygous butterflies (C g C b ) are partially green and blue and the field is full of these butterflies equally distributed. When a bird is introduced in the field, as a predator, and uses color vision to pick its prey, then both green and blue butterflies are picked off because of the bird’s clear color vision. On the other hand, the heterozygous butterflies are camouflaged therefore not easily seen by the bird. When this is repeated, the genotype of the population distribution will change. However, if the homozygous butterflies are equally selected, then the allele frequencies will remain at equilibrium reflecting on the Hardy-Weinberg law.
References
Salanti, G., Amountza, G., Ntzani, E. E., & Ioannidis, J. P. (2005). Hardy–Weinberg equilibrium in genetic association studies: an empirical evaluation of reporting, deviations, and power. European journal of human genetics , 13 (7), 840.
Waples, R. S. (2014). Testing for Hardy–Weinberg proportions: have we lost the plot?. Journal of Heredity , 106 (1), 1-19.
