In population genetics, fixation occurs when every individual within a population has the same allele at a particular locus. The allele, such as a single point mutation or whole gene, will be initially rare (e.g. originating in one individual), but can spread through the population by random genetic drift and/or positive selection. Once the frequency of the allele is at 100%, being possessed by each member, it is said to be "fixed" in the population. Similarly, genetic differences between taxa are said to have been fixed in each species.
References
- Gillespie, J.H. (1994) The Causes of Molecular Evolution. Oxford University Press Inc., USA.
- Hartl, D.L. and Clark, A.G. (2006) Principles of Population Genetics (4th edition). Sinauer Associates Inc., USA.
- Kimura, M. (1962) On the Probability of Fixation of Mutant Genes in a Population. Genetics 47: 713–719. PubMed Central
