Gene Pool, Alleles and Variation in the Population. Genes have many different forms (alleles). This forms the basis of the study of population genetics. Populations are made up of members of the same species which interbreed.ecombination (Crossing Over). This is the exchange of genetic material between adjacent chromatids on the homologous chromosomes. This random exchange of DNA results in many new combinations of alleles on chromosomes, creating great potential for variation.