Stickleback Practice Test

The main idea is that historical selection can leave lasting traces in the genome that stick around even after the selective pressure has ended. When a beneficial allele sweeps through a population, nearby variants can hitchhike with it, creating a sweep that reduces genetic diversity and creates extended regions of linkage. After selection ends, recombination gradually erodes these patterns, but remnants—like unusually high frequencies of certain alleles and lower diversity in the surrounding region—can persist as a “ghost” of the past selection. Those genomic signatures let us infer that adaptation occurred in the past, even though the current conditions no longer favor that allele. So the best description is that past selection leaves detectable signatures in the genome, such as elevated allele frequencies or reduced diversity, even after selection ends. The other options don’t capture this idea: phenotypic changes disappearing isn’t about lingering genomic traces, the notion that ghosts cause spurious signals misstates the concept, and it’s false to say selection leaves no genomic signature at all.