Which event can lead to a genetic bottleneck?

A genetic bottleneck occurs when a significant reduction in the size of a population results in a loss of genetic diversity. This typically happens due to a catastrophic event, such as a natural disaster or epidemic, that drastically decreases the number of individuals in a population. When the population shrinks significantly, only a small sample of the gene pool remains, which can lead to reduced genetic variation in future generations. This reduced genetic diversity can make the population more vulnerable to environmental changes and diseases.

The other options relate to different genetic and evolutionary concepts. For instance, increased gene flow typically promotes genetic diversity rather than constraining it. Stabilizing selection tends to favor intermediate phenotypes and can maintain or narrow genetic variation, but it does not necessarily lead to a bottleneck. The founder effect, while it can lead to reduced genetic diversity, refers to a situation where a new population is established by a small number of individuals from a larger population, which differs from the abrupt size reduction characteristic of a bottleneck.