USA Biology Olympiad (USABO) Practice Exam

Which of the following statements does NOT align with the Hardy-Weinberg equilibrium principle?

1. Dominant alleles are expressed more frequently than recessive alleles

2. No mutations occur

3. Mating is random within the population

4. The population is sufficiently large to prevent genetic drift

The correct answer is: Dominant alleles are expressed more frequently than recessive alleles

The Hardy-Weinberg equilibrium principle outlines specific conditions under which a population's allele and genotype frequencies remain constant from generation to generation in the absence of evolutionary influences. According to this principle, one of the key assumptions is that all alleles, whether dominant or recessive, contribute equally to the genotype's representation in the population, provided that other conditions are met. The statement that dominant alleles are expressed more frequently than recessive alleles suggests a bias in allele visibility based on dominance, which contradicts the premise of the Hardy-Weinberg model. In the equilibrium state, the expression of alleles does not favor dominance; instead, it reflects a balance between all alleles present in the population, regardless of their dominance or recessiveness. The other statements align with the Hardy-Weinberg equilibrium principles: no mutations imply stability in the gene pool; random mating prevents selective breeding effects; and a large population size minimizes the impact of genetic drift, ensuring that allele frequencies remain stable. Therefore, the only assertion that contradicts the balanced allele expression is that dominant alleles occur more frequently than recessive alleles.