Final answer:
Genetic drift refers to random changes in allele frequencies particularly impacting small populations, where chance events like natural disasters can cause significant fluctuations and potentially eliminate alleles through the bottleneck effect.
Step-by-step explanation:
Genetic drift is a mechanism of evolution involving a random change in allele frequencies within a population's gene pool. This phenomenon most commonly affects small populations, where chance events can lead to large fluctuations in allele frequencies from one generation to the next. For example, if an allele is present in a small population and a few individuals with that allele do not reproduce simply due to chance, that allele's frequency can significantly decrease or even be lost in the population. The randomness is akin to pulling out a Snickers bar from a bucket of Halloween candy; it's not influenced by the 'fitness' of the candy but rather by chance.
Genetic drift can be intensified by events such as natural disasters, which may disproportionately affect certain individuals irrespective of their genetic traits, leading to the bottleneck effect. This effect can result in dramatic shifts in genetic variation and can even eliminate alleles from the gene pool. As population size decreases, the impact of genetic drift increases, since fewer individuals are contributing to the next generation’s gene pool, thus amplifying the significance of random changes.
Overall, the smaller the population, the greater the influence of genetic drift on its genetic composition. This is because in large populations, the random loss or survival of alleles has a minimal impact due to the large number of individuals contributing alleles to the next generation. Thus, genetic drift's impact is inversely proportional to population size.