Which type of genetic variation is most associated with rapid, repeatable divergence in sticklebacks?

• A. De novo mutations
• B. Standing genetic variation
• C. Gene flow
• D. Polyploidization

Answer: (B)

The best answer reflects how existing genetic variation within a population can be used by natural selection to drive quick, repeated changes when the environment shifts. In sticklebacks, many freshwater populations repeatedly evolve similar traits, like lighter armor plating or changes in pelvic structure, by shifting the frequencies of alleles that were already present in the ancestral marine population. Because these alleles are already in the gene pool, adaptation can occur rapidly and in parallel across different populations facing similar freshwater pressures.

De novo mutations, while they can contribute, would have to arise independently in each population and then sweep to high frequency, which is slower and less predictable. Gene flow tends to mix populations and can hinder divergence rather than promote rapid, repeatable differences. Polyploidization involves genome doubling and isn’t the typical driver of this kind of rapid, repeated divergence in sticklebacks.