Final answer:
Mutation, genetic drift, migration, and natural selection can all lead to the fixation of an allele in a population. Genetic drift can cause random fluctuations in allele frequencies, especially in small populations. Factors that disrupt Hardy-Weinberg Equilibrium, such as non-random mating or a small population size, can also cause changes in allele frequencies.
Step-by-step explanation:
The evolutionary processes that can lead to the fixation of an allele within a population include mutation, genetic drift, migration (gene flow), and natural selection.
Mutation can introduce new alleles to a gene pool, as seen when a mutation in a rabbit population creates a novel fur color allele. Genetic drift describes random fluctuations in allele frequencies, which can lead to allele fixation purely by chance, especially in small populations. This can occur through events like the founder effect or population bottlenecks. Migration brings new alleles into a population through immigration, potentially altering allele frequencies over time. Lastly, natural selection favors certain alleles that provide a reproductive advantage, increasing their frequency until potentially leading to fixation.
While all these mechanisms can affect allele frequencies, the Hardy-Weinberg Principle describes a state of genetic equilibrium where allele frequencies remain constant. A violation of any assumptions of this principle, such as non-random mating or small population size, can lead to changes in allele frequencies, possibly resulting in fixation of an allele.