What event drastically reduces a population size, leading to potential changes in allele frequencies?

The event that drastically reduces a population size and leads to potential changes in allele frequencies is known as the bottleneck effect. This phenomenon occurs when a population experiences a significant reduction in size due to environmental events, such as natural disasters, disease outbreaks, or human activities. As a result of this drastic reduction, the genetic diversity of the population is often severely diminished.

When a population undergoes a bottleneck, the surviving individuals may not represent the full genetic diversity of the original population. Consequently, the allele frequencies in the surviving population can shift dramatically, which can lead to a loss of genetic variation. This can impact the population's ability to adapt to future environmental changes, thereby affecting its long-term survival and evolutionary trajectory.

While the founder effect refers to the establishment of a new population by a small number of individuals, and migration and genetic drift describe other processes influencing allele frequencies in populations, it is the bottleneck effect that specifically highlights the consequences of a significant decline in population size leading to altered genetic makeup.