Which of the following scenarios represents genetic drift?

Genetic drift refers to random changes in allele frequencies within a population, particularly those that occur in small populations. This phenomenon is often a result of random sampling effects, where certain alleles may become more or less common simply by chance rather than through natural selection.

In the scenario of a meteorite impacting a small island's population, a significant and random event can drastically reduce the population size, leading to a loss of genetic variation and altering allele frequencies simply due to the individuals that survive or fail to reproduce. This is a classic example of genetic drift because the survivors may not represent the genetic makeup of the original population, leading to a shift in allele frequencies purely due to an unexpected and random event.

The other options describe different mechanisms of evolutionary change. Migration involves gene flow between populations which can introduce or remove alleles, while natural selection operates based on differential survival and reproduction of individuals with varying traits. The flow of alleles through a population also typically relates to processes such as migration or mutation rather than the random effects central to genetic drift. Thus, the impact of a meteorite symbolizes a random event that can cause changes in genetic composition without regard to the fitness of the individuals affected, exemplifying genetic drift perfectly.