Final answer:
Random genetic drift has a greater impact on small populations because each individual's genetic material makes up a larger fraction of the total gene pool. Random events, like the premature death of an individual or a natural disaster, can cause significant shifts in genetic structure, leading to the bottleneck effect.
Step-by-step explanation:
Random genetic drift is much more effective in small populations. In such populations, each individual's genetic contribution to the next generation is proportionally larger compared to a large population, resulting in greater susceptibility to chance events that can alter the population's genetic structure. For example, if an individual with unique alleles in a population of 10 dies without reproducing, 10% of the genetic diversity is lost instantly. In a population of 100, the loss would only be 1%, which is less impactful.
Furthermore, genetic drift can significantly affect allele frequencies within a population. This is especially true in smaller populations where random events, like the death of an individual or a natural disaster, can dramatically shift the genetic structure. Such events can lead to the bottleneck effect, where a large portion of the genetic diversity is lost, and the genetic structure of the surviving individuals defines the new population.