what affect the gene frequency

Gene frequency can be affected  by

1. Gene migration or gene flow

 2. Genetic drift 

3. Mutation

4. Genetic recombination 

5. Natural selection 

Gene flow is the transfer of alleles of genes from one population to another. 

It results in increase in frequency of that allele in the second population. In this way, gene frequency is not maintained. In same way other four factors also affect the gene frequency.