Final answer:
The student's question pertains to genetic drift, which can cause an allele to become fixed in a population by chance without necessarily being beneficial. Genetic drift has greater effects in small populations and occurs due to random reproductive success and survival, which can drastically change allele frequencies independently of allele advantages.
Step-by-step explanation:
The student is asking about genetic drift and its impact on allele frequencies within a population. Specifically, the question is referring to the scenario where an allele can become fixed but never beneficial purely due to chance events rather than because of natural selection. Genetic drift is a mechanism of evolution that involves random fluctuations in allele frequencies, which can have a more pronounced effect in small populations.
Chance events such as natural disasters, random mating, and mortality can contribute to genetic drift. An allele may become more prevalent or even fixed in a population simply because the individuals that carry it reproduce more by chance, not because the allele confers any survival or reproductive advantage. On the other hand, beneficial alleles are those that provide a selective advantage to individuals, increasing their chances of survival and reproduction.
The classic example used to explain genetic drift is the case of a population where a randomly occurring event, such as a natural disaster, disproportionately affects carriers of a certain allele, thereby changing the allele frequency. Such changes are independent of the allele's effect on fitness. A genetic drift can even lead to the elimination of an allele, which might be less likely to happen with natural selection if the allele was beneficial.