Final answer:
True, strong bottlenecks can reduce heterozygosity within populations by causing a loss of genetic variation when a large portion of a population is killed in events like natural disasters, leading to a change in the genetic structure of the surviving population.
Step-by-step explanation:
True, strong bottlenecks can indeed reduce the heterozygosity within populations. A bottleneck effect occurs when a population's size is significantly reduced for at least one generation. This reduction can be due to various factors, including natural disasters like earthquakes or hurricanes. Such events can result in a loss of genetic variation because the surviving population is often a random sample of the original group. This can dramatically change the genetic makeup, with some alleles being lost and the frequency of others changing, which can lead to inbreeding and a consequent decrease in heterozygosity.
The bottleneck effect and founder effect both cause significant shifts in population genetics. During a bottleneck, the genetic structure can change due to the random elimination of individuals. The surviving genotypes dictate the genetic structure of the post-disaster population, which might be quite different from the original population's genetic makeup.