Medical College Admission Test (MCAT) Practice Exam

The bottleneck effect refers to a sharp reduction in the size of a population due to environmental events, such as natural disasters. This phenomenon can significantly affect the genetic structure of populations.

When a natural disaster occurs, it often dramatically reduces the population size by eliminating numerous individuals regardless of their genetic traits. The survivors may not represent the genetic diversity of the original population. As a result, this drastic decrease in population size leads to a loss of genetic variation. The gene pool is thus reduced to only the alleles present in the surviving members, which may be a very limited subset of what previously existed.

This reduction in genetic variation can have long-term consequences for the population, including decreased adaptability to environmental changes and an increased risk of extinction. Therefore, the correct answer highlights how a natural disaster can significantly reduce genetic variation within a population, illustrating the major implications of the bottleneck effect on a gene pool.