Equilibrium or the Hardy-Weinberg law is the central concept of population genetics. It is a principle that encompasses several concepts that must be mentioned and analyzed to obtain a general and complete understanding of this principle. Among the most important concepts we find: Population genetics, Allelic frequencies and Genotypic frequencies.
- Population genetics: it is the study of the distribution of genetic variations that a population presents and the ways in which the frequencies of genes and genotypes are maintained or changed in said population. Likewise, it is closely linked to multiple genetic and environmental factors that in one way or another determine the frequency and distribution of alleles and genotypes in families and communities.
- Allelic frequency: it is the proportion that is observed of a specific allele with respect to the set of those that can occupy a given locus in a population. That is, it is the number of "A" or "a" alleles (independently) of the total number of A alleles and one present in a given population.
- Frequency Genotype: frequency or proportion of genotypes in a population. That is, of the total number of possible genotypes in a population (AA, Aa, aa) how many are AA, Aa and aa.
A sample of individuals, of known genotype from a population, can be used to infer the estimate of allele frequencies, simply by counting the alleles in the individuals with each genotype. This question arises, is it possible to calculate genotype frequencies from allele frequencies? Actually, it is not that simple, as it is not known how the alleles are distributed between homozygous and heterozygous. But to solve this great dilemma, there is a simple mathematical relationship called the Hardy-Weinberg Balance, whose application allows us to know and find the genotypic frequencies (homozygous and heterozygous distribution in the population) of the allelic frequencies.
The Hardy-Weinberg equilibrium postulates that: in a sufficiently large panmictic population and in the absence of evolutionary forces that affect it, the genotype and genotype frequencies remain constant from generation to generation. This balance will be applied in ideal populations, in which:
- The size of the population is large enough or it is infinite.
- Organisms in the population reproduce randomly.
- There is a sexual reproduction.
- The organisms are diploid.
In contrast, the Hardy-Weinberg equilibrium will not apply to a population if:
- There is natural selection.
- There is migration, gene flow between populations.
- There is a mutation.
- There is a genetic drift.
