Answer

Bottleneck events reduce the size of the population and greatly reduce genetic variation.

Explanation

A bottleneck event is a sharp reduction in the size of a population due to environmental events or human activities. This sudden decrease in population size can cause a corresponding decrease in genetic variation. This is because the surviving population is likely to be genetically less diverse than the original population, due to genetic drift. Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance (sampling error). During a bottleneck event, many alleles, or gene variants, may be lost, reducing the genetic variability of the population. This can have long-term effects on the population, including reduced adaptability to new environmental conditions and increased susceptibility to genetic diseases.