Unit 11 - III. Forms of Natural Selection

Genetic equilibrium is a condition in which

allele frequencies in a population don’t change from 1 generation to the next

With genetic equilibrium, the rate of trait occurrence

remains constant (no evolution occurs)

Evolution

disruption of genetic equilibrium

Directional selection

extreme phenotype becomes a favorable adaptation

Directional selection is usually caused by

a change to the environment/migration to new habitats

Stabilizing selection

average phenotypes become more favorable → extreme phenotypes become more unfavorable

Stabilizing selection usually inhibits the

rate of evolution bc of a narrowed range of variation

Disruptive selection (rare form of natural selection)

extreme phenotypes become more favorable than average phenotypes

• creates 2 separate subpopulations