<P> A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events (such as earthquakes, floods, fires, disease, or droughts) or human activities (such as genocide). Such events can reduce the variation in the gene pool of a population; thereafter, a smaller population, with a correspondingly smaller genetic diversity, remains to pass on genes to future generations of offspring through sexual reproduction . Genetic diversity remains lower, increasing only when gene flow with another population occurs or very slowly increasing with time as random mutations occur . As a consequence of such population size reductions and the loss of genetic variation, the robustness of the population is reduced and its ability to adapt to and survive selecting environmental changes, like climate change or a shift in available resources, is reduced . Alternatively, if by chance survivors of the bottleneck are the individuals with the greatest genetic fitness, the frequency of the fitter genes within the gene pool is increased, while the pool itself is reduced . </P> <P> The genetic drift caused by a population bottleneck can change the proportional distribution of allele s by chance and even lead to fixation or loss of alleles . Due to the smaller population size after a bottleneck event, the chances of inbreeding and genetic homogeneity increase, leading to the potential for inbreeding depression to occur . Smaller population size can also cause deleterious mutations to accumulate </P>

Loss of diversity in a reduced population is called