What does FST primarily assess in population genetics?

• A. Genetic differentiation of quantitative traits
• B. Adaptive divergence among species
• C. Genetic differentiation at neutral markers
• D. Gene flow between habitats

Answer: (C)

FST measures how different populations are in their allele frequencies, using neutral genetic markers. It compares how much genetic variation exists within populations to the total variation across populations. Because neutral markers aren’t usually affected by natural selection, the differentiation reported by FST mostly reflects genetic drift and the level of gene flow between populations. When gene flow is strong, allele frequencies mix and FST is low; when gene flow is limited and drift acts independently, FST increases, indicating greater differentiation. This is why FST is considered a measure of neutral genetic differentiation, serving as a baseline to compare with differentiation in other traits to infer selection.