In which condition the gene ratio remains constant for any species population?
Allele frequency in a population can remain constant only if individuals of the population randomly interbreed. Generally, it never happens in nature and species populations exist in small groups of randomly breeding subpopulations. Thus, allele frequency between two subpopulations may differ but that within the subpopulation will remain constant. Such subpopulations are termed Mendelian populations or deme. Exchange of genes between demes takes place occasionally.
Mutation, gene flow (due to migration), etc. may tend to change the allele frequency of the subpopulation.