Meiosis is the process of the production of 4 non-identical gametes with 1n chromosome. It occurs in 2 stage with two separation: The first separation is the separation of homologous chromosomes and the second separation is the separation of sister chromatids. New combinations of alleles are formed from homologous chromosomes forming a bivalent and forming a chiasmata with equal lengths of chromosomes being exchanged, hence creating variety in organisms. Independent segragation and crossing over increase genetic diversity.
Genetic diversity is the number of different alleles of a gene in a population. Genetic diversity is a factor enabling natural selection to occur. Natural selection occurs due to a selection pressure in an environment due to mutations. Those with an advantageous allele are more likely to survive and reproduce and pass on the allele to the offspring. The frequency of the advantageous allele increases in the population over many generations.
There are 3 types of natural selection: Stabilising selection, disruptive selection and directional selection.