Microevolution Microevolution is the Change in allele frequency due to one of the following processes: Natural Selection Mutations Genetic Drift Gene flow

Types of Natural selection Direction Selection Selection favors one of the extreme types in the population. Often the result in directional changes in the environment Examples: Pesticide and antibiotic resistance

Types of Natural Selection cont. Stabilizing Selection Selection favors the intermediate forms while selecting against the extremes. Occurs in stable environments in which organisms are well adapted

Types of Natural Selection cont. Disruptive Selection Selection favors both extremes while the intermediate forms are selected against. Over long periods of time disruptive selection may lead to speciation.

Sexual Selection Individuals will select potential mates according to specific characteristics. These traits may or may not be healthy for the species. Example: Irish Elk

Mutations Mutations are the raw material for all new alleles. New mutations will change gene frequency. Natural selection will either amplify or diminish mutations in a population.

Genetic Drift Genetic drift is a random change in allele frequencies over the generations, brought about by chance events. Genetic drift is most powerfully felt in small populations. The founder effect and the bottleneck effect are two examples where genetic drift changes allele frequency in a population.

Founder Effect The founder effect occurs when a small group becomes isolated from its larger population. The new group will likely have a different allele frequency than the parent group it originated from. Example: Mutiny on the Bounty

Bottleneck A bottleneck is a severe reduction in a population brought about by intense selection pressure or some natural calamity. The population is regenerated by means of the few individuals left. The genetic diversity is greatly diminished compared to the original population.

Gene Flow The movement of alleles between different populations of the same species. Alleles are lost from a population when individuals leave (emigrate). Alleles enter a population when new individuals move in (immigrate)