Hardy – Weinberg principle states that the sum of allelic frequencies in a population remains constant.

Five factors are known to affect Hardy-Weinberg equilibrium.

These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection.

$(i)$ Gene migration or gene flow : When migration of a section of populations to another place occurs, gene frequencies change in the original as well as in the new population.

New genes/alleles are added to the new population and these are lost from the old population.

$(ii)$ Genetic drift : It refers to the elimination of the genes of certain traits when a section of population migrates or dies of natural calamity.

$(iii)$ Mutation : The sudden heritable change which is direction less in gene and alter the genetic makeup of an individual.

$(iv)$ Genetic recombination : It occurs during gamete formation when chromosomes pass from parent to offspring.

$(v)$  Natural selection : It is an phenomenon by which some numbers of the population having traits that enable them to grow and reproduce at higher rate are favoured.