BIOLOGY Volume 3 - A Guide to General Biology - 2004

27. MECHANISMS OF SPECIATION

27.1. Population Genetics

27.1.3. Genotype Frequencies

The frequencies of individual alleles within a Gene pool allow researchers to calculate genetic changes in a given population and determine genotype frequencies. Because an Organism's genotype is the primary factor determining its phenotype, calculating genotype frequency is used to predict the potential outcomes of specific crosses. This holds significant practical importance for agriculture and medicine.

The mathematical relationship between allele and genotype frequencies in populations was established in 1908, independently of one another, by the English mathematician G. H. Hardy and the German physician W. Weinberg. This relationship, known as the Hardy–Weinberg equilibrium, can be formulated as follows:

“The frequencies of dominant and recessive alleles in a given population will remain constant from generation to generation in the presence of certain conditions.”

These conditions are as follows:

1) the population size is large;

2) mating is random;

3) no new Mutations arise;

4) all genotypes are equally fertile, i. e., no Selection occurs;

5) generations do not overlap;

6) there is neither emigration nor immigration, i. e., no gene flow occurs between the given population and other populations.

Consequently, any changes in allele frequency must be driven by the violation of one or more of the conditions listed above. Such violations can trigger evolutionary changes, and when these changes take place, they can be studied and their rates measured using the Hardy–Weinberg equation.