∞ generated and posted on 2016.12.15 ∞
Process by which an allele becomes the only allele found at a given locus within a gene pool.
| Fixation is when a certain gene variety becomes, in a species or population, the only variety of that gene that remains. |
Such an allele is said to be fixed. Fixation results in the loss of genetic variation otherwise associated with a locus.
To a degree this loss of variation that is associated with fixation is that of less-well adapted alleles, then fixation will result in an increase in the average fitness of a population. That increase, however, may be an only short-term phenomena that is observed only absent environmental change since genetic diversity is also an important component of a species' fitness.
Figure legend: Climb of allele from point of entrance into population at very low frequency on up to the point of fixation (all other alleles at same locus are present at best in very low frequencies). Note the passage through polymorphism on the way from rare to fixed.
Figure legend: Climb of allele from point of entrance into population at very low frequency on up to the point of fixation (all other alleles at same locus are present at best in very low frequencies) including in terms of passage through polymorphism on the way from rare to fixed. Note both the ongoing and increasing potential for that allele to serve as the basis for mutational formation of a new allele at the same locus (straight arrows).
Figure legend: Climb of allele from point of entrance into population at very low frequency on up to the point of fixation (all other alleles at same locus are present at best in very low frequencies) including in terms of passage through polymorphism on the way from rare to fixed. Note the < *https://en.wikipedia.org/wiki/Bar_graph>bar graphs which provide explicit indication of relative allele frequencies, assuming a one-locus, two-allele system.
Alternatively, fixation can result in the loss of potentially beneficial alleles from a population, either because beneficial alleles were lost due to genetic drift (random extinction of alleles) or instead because alleles are lost that are not currently beneficial but which could be given environmental change.
Thus, while fixation can be the consequence of a triumph of better adapted individuals, in actuality the fixation of alleles found at too many of a species' loci can be an indication of a population that is in trouble since they will have a reduced potential to adapt to environmental change.