A population of birds encounters a dramatic event that results in a severe decrease in population size. As a result of the newly decreased population, what type of genetic drift does this population now exhibit?

Explanation

The bottleneck effect is an extreme example of genetic drift that happens when the size of a population is severely reduced. The allele frequencies in the group of surviving individuals may be very different from those of the population prior to the event, and some alleles may be missing entirely. The smaller population will also be more susceptible to the effects of genetic drift for generations (until its numbers return to normal), potentially causing even more alleles to be lost. How can a bottleneck event reduce genetic diversity? Imagine a bottle filled with marbles, where the marbles represent the individuals in a population. If a bottleneck event occurs, a small, random assortment of individuals survive the event and pass through the bottleneck (and into the cup), while the vast majority of the population is killed off (remains in the bottle). The genetic composition of the random survivors is now the genetic composition of the entire population.