What is the long-term fate of a locus carrying two alleles, one with a fitness advantage, under natural selection?

The long-term fate of a locus with two alleles, where one allele confers a fitness advantage, is that the beneficial allele will typically become fixed in the population. This process occurs due to the differential reproduction of individuals carrying the advantageous allele compared to those carrying the less fit allele.

When natural selection favors one allele, individuals with that allele tend to have higher reproductive success. Over successive generations, this leads to an increase in the frequency of the beneficial allele within the population. As this allele continues to provide a fitness advantage, it will gradually replace the less advantageous allele until it becomes the only allele present at that locus in the population, a situation referred to as fixation.

Fixation may not be immediate and can be influenced by various factors such as mutation, genetic drift, and gene flow, but under strong selection for the beneficial allele, the likelihood of its fixation increases significantly. Thus, the scenario where the beneficial allele is fixed accurately reflects the dynamics of evolution under natural selection.