Allele frequencies in a population are stable and are constant from generation to generation. 

OR 

Allele frequency or gene frequency in a population (gene pool) remains constant from generation to generation unless there are factors to upset it. 

Role of factors that affect Hardy – weinberg equilibrium. Gene flow: It is the movement of genes or alleles from one population to another when there is a migration of a section of population to another place and population this changes gene frequencies. 

Genetic drift: It is the random ‘ change in the gene frequency by chance (in small populations). The change in gene frequency in the new population may be so different that the members become a different species (founder’s effect). 

Mutation: It is the sudden hertitable change in genetic material which results in new genotypes and phenotypes, thus altering the gene frequency. 

Genetic recombination: It occurs during gametogenesis (meiosis) and results in variations. This would result in gene frequency over a period of time. 

Natural selection: Variations that occur as a result of mutations or recombinations or due to gene flow or genetic drift inhance reproductive success or fitness survivors would – leave more progeny and over a period of time the gene frequency of the population change.