The bottleneck effect is a type of genetic drift that occurs when a population undergoes a drastic reduction in size due to a random event such as a natural disaster, disease outbreak, or human interference. This reduction in population size can lead to a loss of genetic diversity, as certain alleles may be lost or become more common due to chance. As a result, the genetic makeup of the population may be significantly different from the original population, and this can have long-term effects on the population's ability to adapt to changing environmental conditions.