Directional selection
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[edit] Immunology
In immunology positive selection is when: developing T-cells are selected for recognition of self MHC (and sef peptides). This ensures an immune response can develop. Followed by negative selection.
[edit] Genetics
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.
[edit] 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.
