Hardy-Weinberg equilibrium will NOT occur in a population in which which of the following conditions is present?

• A. Individuals preferentially mate with certain phenotypes (nonrandom mating).
• B. There is no differential survival or reproduction among genotypes (no natural selection).
• C. No alleles enter or leave the population (no migration/gene flow).
• D. The population is very large, minimizing genetic drift.

Answer: (A)

Verified step by step guidance

1. Understand that Hardy-Weinberg equilibrium describes a state where allele and genotype frequencies in a population remain constant from generation to generation, provided certain conditions are met.
2. Recall the five main conditions required for Hardy-Weinberg equilibrium: no mutation, random mating, no natural selection, extremely large population size (no genetic drift), and no gene flow (no migration).
3. Identify that nonrandom mating (individuals preferentially mating with certain phenotypes) violates the random mating condition, which is essential for Hardy-Weinberg equilibrium.
4. Recognize that the other conditions listed (no natural selection, no migration, large population size) support Hardy-Weinberg equilibrium and do not prevent it from occurring.
5. Conclude that the presence of nonrandom mating disrupts Hardy-Weinberg equilibrium because it changes genotype frequencies by favoring certain phenotypes over others.