Apply natural selection by allowing only the following proportions of individuals exhibiting each genotype to survive.
Natural selection is a process of change in phenotype and genotype in population over some generations. This mechanism allows to survive organisms that possess certain traits and genotype. But natural selection does not affect genotype directly. This interaction is mediated with phenotype and fitness. Fitness is an ability of an organism possessing certain alleles (genotype) to survive. This certain genotype increases the fitness and surviving of an organism and determines a phenotype or a reproduction rate connected directly with natural selection. There are several types of natural selection. But most of them lead to loss of genetic variation as unfit alleles are "weeded out" of the population. Only balancing selection (also negative frequency-dependent selection) preserve genetic variation and allow different genotype to survive. The main reason is that balancing selection imply that the heterozygous genotype has the highest fitness and preserves dominant and recessive alleles.