Microevolution is the change in the genetic makeup of the gene pool of a population. It refers to the change in allelic frequencies that occur from generation to generation. There are three ways that microevolution can occur: mutation, genetic drift and natural selection. Mutation is the change in a gene of the DNA of an organism. This may change an allele and possibly the alleles frequency in the gene pool of the population. Genetic drift is an unpredictable change in a populations allelic frequencies from generation to generation. Genetic drift is also a change by chance. An example is the founder affect, in which a small group from a population settles into an area that is isolated from the original population and pass down their genes from a smaller, more restricted gene pool. Another example is the bottleneck effect, in which a natural disaster or sudden change in climate selects out a large amount of the population, changing and decreasing the gene pool dramatically. Natural selection is the selection of organisms based on their reproductive success. If an organism is better suited for reproduction than another then its genes and alleles will be passed on to the next generation.
Macroevolution is the origin of new taxonomic groups. The diff bn microevolution and macroevolution is that microevolution is changes that are only within one gene pool and only affects the genes and allele frequencies of a species or population while macro describes how species evolve from one another. It is change above the species level and affects appearance.