Final answer:
The bottleneck effect occurs when a natural disaster dramatically reduces a population's size, leading to a random sampling of survivors that alters the population's genetic structure.
Step-by-step explanation:
An example of the bottleneck effect could be when a natural disaster like an earthquake or hurricane suddenly wipes out a large portion of a population. The survivors are usually a random sampling of the original group, which can result in a significant change in the population's genetic structure. This effect demonstrates how genetic drift can occur through dramatic, random reductions in population size, thereby altering allele frequencies and reducing genetic variability.
The bottleneck effect is distinct from the founder effect in that it occurs after a drastic reduction in population size due to an event like a natural disaster, while the founder effect happens when a new population is established by a small number of individuals from a larger population. Both effects can significantly change the genetic makeup of a population, but the bottleneck effect specifically reduces or eliminates alleles within a population rather than introducing them.