Alleles present in a population at a given period are referred to as the gene pool. It is the total amount and variety of genes and alleles available for transmission to the next generation in a sexually reproducing population. In comparison to formal taxonomy, Harlan and Wet identified types of gene pools as main, secondary, tertiary, and quaternary gene pools for the classification of each crop and its related species. The total quantity of genes, types and variants of genes, proportion, and distribution of genes are all revealed by studying the gene pool of a population. Selection, mutation, gene flow, and genetic drift are evolutionary mechanisms that influence a population’s gene pool. The number of genes and the number of people who carry these genes determine the size of the gene pool. Because of chance events, the number of each gene in a gene pool might shift over time. As a result, the goal of this review study is to evaluate the gene pool, classification, and importance of the gene pool in modern crop development programs.