Explain what microevolution is? What are the three ways that variation occurs?

Microevolution refers to any evolutionary change below the level of species. It also refers to changes in the frequency within a population or a species of its alleles (alternative genes). Mutations alter the order of bases in the nucleotides of DNA. Mutations are likely to be rare and most mutations are probably harmful, but in some instances the new alleles can be favored by natural selection independent assortment (recombination of chromosomes that occurs during sexual reproduction) and the Crossing over that happens during meiosis.