Which of the following statements best describes frequency-dependent selection?

• A. Individuals with intermediate traits have higher fitness than those with extreme traits.
• B. The fitness of a phenotype depends on how common or rare it is in the population.
• C. Natural disasters randomly reduce population size, altering allele frequencies.
• D. A single allele provides a consistent advantage regardless of its frequency.

Answer: (B)

Verified step by step guidance

1. Understand the concept of frequency-dependent selection: It refers to a situation where the fitness of a phenotype depends on its frequency in the population. This means that the advantage or disadvantage of a trait changes based on how common or rare it is.
2. Eliminate incorrect options by analyzing their definitions: For example, the statement 'Individuals with intermediate traits have higher fitness than those with extreme traits' describes stabilizing selection, not frequency-dependent selection.
3. Evaluate the statement 'Natural disasters randomly reduce population size, altering allele frequencies': This describes genetic drift, specifically a bottleneck effect, and is unrelated to frequency-dependent selection.
4. Analyze the statement 'A single allele provides a consistent advantage regardless of its frequency': This describes directional selection, where one allele is consistently favored, and does not depend on its frequency.
5. Conclude that the correct statement is 'The fitness of a phenotype depends on how common or rare it is in the population,' as this directly aligns with the definition of frequency-dependent selection.