National League for Nursing (NLN PAX) Practice Exam

During which phase of population evolution does isolation occur according to the Hardy-Weinberg principle?

1. Genetic drift

2. Mutation

3. Isolation

4. Natural selection

The correct answer is: Isolation

Isolation is a critical phase in population evolution as defined by the Hardy-Weinberg principle, which asserts that equilibrium in a population should occur in the absence of evolutionary forces. This principle includes five key assumptions: no mutations, no migration, a very large population size (which eliminates genetic drift), random mating, and no natural selection. Isolation refers to the separation of a population into distinct groups that do not interbreed, leading to reproductive isolation. This can happen physically (geographic isolation) or behaviorally (ethological isolation), ultimately allowing different genetic variations to develop independently. Over time, these isolated groups may evolve into distinct species due to the lack of gene flow between them, making isolation a fundamental aspect of evolutionary change. In contrast, options like genetic drift, mutation, and natural selection are natural processes that can occur within a non-isolated population. Genetic drift involves random changes in allele frequencies, mutation introduces new genetic variations, and natural selection favors certain traits over others, but these processes do not specifically denote the isolation phase itself. Thus, isolation plays an essential role in understanding how evolutionary changes can occur without the influence of gene flow from adjacent populations.