Balancing selection

Balancing selection: Selection involving opposing forces in which selective advantages and disadvantages cancel each other out.

Balancing selection is rare in natural populations. [balancing selection: selection favoring heterozygotes] Only a handful of other cases beside the sickle-cell example have been found.

Finally, a number of forms of balancing selection exist, which do not result in fixation, but maintain an allele at intermediate frequencies in a population.

This situation, where selection actively maintains two or more alleles at a locus, is called balancing selection. Balancing selection can arise by the heterozygotes having a selective advantage, as in the case of sickle cell anemia.

See also: Selection, Gene, Population, Organ, Species