Final answer:
Small populations are more susceptible to decreased genetic diversity due to the founder effect, where the gene pool is influenced by a small number of founders, and genetic drift, which includes stochastic processes like the bottleneck effect resulting from natural disasters.
Step-by-step explanation:
Small populations are susceptible to two main factors that can decrease genetic diversity: the founder effect and genetic drift due to stochastic processes like natural disasters.
The founder effect occurs when a small group of individuals establishes a new population, and the genetic traits of the founders disproportionately influence the gene pool. This was seen in the Afrikaner population in South Africa, where a small group of Dutch settlers exhibited a higher frequency of mutations leading to Huntington's disease (HD) and Fanconi anemia (FA).
Genetic drift is another factor impacting small populations. It is the random fluctuation of allele frequencies, which can occur due to chance events, such as natural disasters, significantly altering the genetic structure of a population. When a disaster strikes randomly, removing a large portion of the gene pool, this is called a bottleneck effect.