Answer:
b. the bottleneck effect.
Explanation:
The bottleneck effect occurs when a population's size is reduced for at least one generation. This will result in a very reduced genetic variation, which can lead to further adaptation problems.
The Founder effect has its similarities (in terms of the resulting reduced genetic pool) with the bottleneck effect, BUT it occurs when a new colony is started by a few members of the original population.
The Hardy-Weinberg equilibrium is a principle in population genetics that states that the genetic variation in a population will remain constant from one generation to the next IF certain conditions are present (no migration, aleatory mating, among others), so this is not the answer.
Genetic drift (refers to the change in the frequency of an existing gene variant in a population due to random sampling of organisms, so it is not the answer.
