Final answer:
The sharp reduction of a population's gene pool due to a severe epidemic is known as the bottleneck effect, which results in decreased genetic variation and alters the genetic structure of the surviving population.
Step-by-step explanation:
The sharp reduction of the gene pool and the numbers of a population through a severe epidemic is an example of the bottleneck effect. The bottleneck effect occurs when a large portion of a population is suddenly wiped out due to a catastrophic event or severe conditions, such as an epidemic, leaving only a small surviving population. By chance, the allele frequencies in the survivors may be different from those in the original population. This results in a decrease in genetic variation and can affect the genetic structure of the future population.