Directional selection

Article summary

In population genetics, directional selection is a mode of natural selection in which individuals with a trait (for example, beak size) at one extreme of a phenotypic distribution have better fitness than individuals with intermediate or opposite extreme phenotypes. Over time, the allele frequencies, and consequently the population mean for the trait, shift consistently in the direction of the extreme phenotype with greater fitness. An example is the evolution of antibiotic resistance in bacteria – the introduction of a strong selective pressure (the antibiotic) selects resistant strains of bacteria, thereby shifting allele frequencies toward phenotypes with strong resistance to the antibiotic. This type of selection plays an important role in the emergence of complex and diversifying traits and is also a primary force in speciation. Natural phenomena that might promote strong directional selection include: * Sudden environmental changes (biotic or abiotic) favouring one phenotype over a previously dominant phenotype; * Colonization of a new habitat with novel selection pressures (as was the case with Darwin’s finches migrating to the Galápagos Islands two million years ago); * The genetic context offers sufficient heritable variation and involves relatively minor interactions or correlations among genes (pleiotropy or epistasis ) and trade-offs (antagonistic pleiotropy).…

Key claims

No claims recorded.

Discussion questions

1. Summarise the article in your own words. Which single claim would you verify first, and why?
2. Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
3. If two sources disagreed about one of these facts, what would you need in order to trust one over the other?

Bibliography

No sources recorded.