Final answer:
Low levels of genetic diversity are usually observed in populations with a small initial population size or populations that are physically isolated for long periods of time. Genetic drift and chance events can also reduce genetic variability within a population.
Step-by-step explanation:
Low levels of genetic diversity are usually observed in populations when there is a small initial population size, decline in genetic diversity may make a population more vulnerable to recessive lethal alleles or changing environmental conditions. Additionally, populations that are physically isolated for long periods of time or cultural groups that practice strict endogamy can also experience low levels of genetic diversity due to genetic drift. Furthermore, chance events or catastrophes can reduce genetic variability within a population.