Final answer:
The assertion that the Hardy-Weinberg principle explains the stability of genetic frequencies in a population is true, but the reason provided is false since the principle assumes no genetic drift. The correct option for this question is C: Assertion is true but reason is false.
Step-by-step explanation:
The assertion that the Hardy-Weinberg principle explains the variations occurring in population and species over a number of generations is true. This principle provides a baseline model for understanding the genetic stability of a population in the absence of evolutionary forces. However, the reason given, stating that the Hardy-Weinberg principle is applicable only when genetic drift occurs, is false. In fact, the principle describes a non-evolving population where genetic drift, along with other evolutionary forces such as mutation, migration, and natural selection, do not occur.
The Hardy-Weinberg principle is represented by the mathematical equation p² + 2pq + q² = 1, where p represents the frequency of the dominant allele and q represents the frequency of the recessive allele. A population is in Hardy-Weinberg equilibrium if it meets certain criteria: no mutations, no gene flow, random mating, no genetic drift, and no selection. When real population data deviate from the expected frequencies derived from this equation, it suggests that the population is evolving due to one or more evolutionary forces.
The correct option for this question is C. The assertion is true but the reason is false.