In population genetics, directional selection (sometimes referred to as positive selection) occurs when natural selection favors a single allele and therefore allele frequency continuously shifts in one direction. It stands in contrast to balancing selection where selection may favor multiple alleles, or purifying selection which removes deleterious mutations from a population. Directional selection is a particular mode or mechanism of natural selection.

Example

• A common example is the evolution of the peppered moth, where the favored direction has noticeably shifted in relation to the effects of humans.

See also

• Stabilizing selection
• Disruptive selection
• Balancing selection

Selection

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