Genes and genotypes of the population

A population is a group of freely interbreeding organisms of the same species, which for a long time live in a certain area apart from other representatives of this species.
Within the population, as a result of crossing, there is a constant exchange of genetic material. Gene exchange between different populations occurs much less frequently. Therefore, each population is characterized by its own specific set of genes and a special ratio of the frequencies of occurrence of different alleles and genotypes.

The collection of all genes and genotypes of a population is called a gene pool.

The gene pools of populations of the same species differ from each other, since in different conditions of existence, different characters are subjected to natural selection. As a result, the internal diversity of the species increases, which allows it to adapt to changing conditions.

Individuals within a population differ in genotypes and phenotypes. If we consider only one trait, then these can be dominant homozygotes (AA), heterozygotes (Aa) and recessive homozygotes (aa). In addition, populations are genetically heterogeneous due to the continuously occurring hereditary variability.

It is impossible to count the genes available in the population, therefore, the composition of the gene pool is judged by the frequency of occurrence of alleles and genotypes.
Allele frequency is its share in the total number of genes that determine a given trait.
Genotype frequency is its share in the total number of individuals in the population.
Consider an example of the population shown in the figure.

The animal population consists of 7 individuals:
2 individuals – dominant homozygotes BB;
3 individuals – Bb heterozygotes;
2 individuals are recessive homozygotes bb.
In total, there are 14 genes in the gene pool, of which 7 are dominant (allele B) and 7 are recessive (allele b).

The frequency of the dominant allele is 7: 14 = 0.5, or 50%.
The frequency of the recessive allele in this case is also 7: 14 = 0.5, or 50%.

The frequency of the dominant homozygote is 2: 7 = 0.286, or 28.6%.
The frequency of recessive homozygote is the same: 2: 7 = 0.286, or 28.6%.
The frequency of the heterozygote is 3: 7 = 0.428, or 42.6%.

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