Balancing Selection and Genetic Polymorphism in Natural Populations
Summary
Balancing selection is a fundamental evolutionary force that maintains multiple alleles at a locus within a population over extended periods. Unlike directional selection, which drives alleles to fixation, balancing selection preserves genetic diversity through a variety of mechanisms, including heterozygote advantage, negative frequency-dependent selection and spatially or temporally varying selection pressures. These processes can result in stable polymorphisms that underpin critical ecological and physiological traits, from disease resistance in vertebrate immune systems to adaptive colour polymorphisms in plants and insects. Modern population genomics has revealed that signatures of balancing selection are often characterised by an excess of intermediate-frequency alleles, elevated linkage disequilibrium around target loci and, in some cases, trans-species polymorphisms that predate speciation events. Advances in sequencing technologies and statistical methods now permit the detection of such signatures across genomes, even in non-model organisms. The global significance of this research spans conservation genetics, where preserved diversity may enhance species resilience to environmental change, to agricultural and medical applications, where understanding maintained polymorphisms can inform breeding programmes or uncover genetic factors underlying pathogen susceptibility.
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Balancing Selection and Genetic Polymorphism in Natural Populations publication trend
The graph below shows the total number of articles in balancing selection and genetic polymorphism in natural populations across all publications each year (not limited to Nature Index journals).
Technical terms
Balancing selection: A mode of natural selection that actively maintains two or more alleles at higher frequencies than would be expected under genetic drift alone.
Genetic polymorphism: The occurrence of two or more distinct alleles of a gene in a population at appreciable frequency.
Heterozygote advantage: A form of balancing selection whereby individuals carrying two different alleles at a locus have higher fitness than homozygotes.
Negative frequency-dependent selection: A mechanism of balancing selection in which the fitness of an allele increases as it becomes rarer in the population.
Spatially varying selection: Selective pressures that differ across habitats or environmental gradients, promoting the maintenance of multiple alleles in a species’ range.
References
- CEGA: a method for inferring natural selection by comparative population genomic analysis across species. Genome Biology (2023).
- Pathometagenomics reveals susceptibility to intestinal infection by Morganella to be mediated by the blood group-related B4galnt2 gene in wild mice. Gut Microbes (2023).
- Balancing selection on an MYB transcription factor maintains the twig trichome color variation in Melastoma normale. BMC Biology (2023).
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