What pattern is observed in the genomic region surrounding the EDA gene in freshwater stickleback populations?

What pattern is observed in the genomic region surrounding the EDA gene in freshwater stickleback populations?

• A. No detectable selection around EDA.
• B. Increased haplotype diversity around EDA.
• C. Random mutation hotspot with neutral effect.
• D. Signatures of positive selection and reduced haplotype diversity around EDA due to selective sweeps for reduced plates.

Answer: (D)

In freshwater sticklebacks, the pattern around the EDA gene reflects positive selection driving the reduced-plates phenotype. When a beneficial EDA variant rises to high frequency or fixation, nearby genetic variants hitchhike with it, shrinking genetic variation in that region. This creates signatures of a selective sweep: reduced haplotype diversity and often extended haplotypes with higher linkage disequilibrium around EDA. The result matches the repeated evolution of plate loss in freshwater environments, where selection favors this trait. Patterns like no detectable selection would not show the narrowing of diversity, while increased haplotype diversity would suggest balancing or neutral processes, not a sweep. A random mutation hotspot with neutral effects wouldn’t consistently align with the adaptive plate-reduction pattern seen across populations.

In freshwater sticklebacks, the pattern around the EDA gene reflects positive selection driving the reduced-plates phenotype. When a beneficial EDA variant rises to high frequency or fixation, nearby genetic variants hitchhike with it, shrinking genetic variation in that region. This creates signatures of a selective sweep: reduced haplotype diversity and often extended haplotypes with higher linkage disequilibrium around EDA. The result matches the repeated evolution of plate loss in freshwater environments, where selection favors this trait.

Patterns like no detectable selection would not show the narrowing of diversity, while increased haplotype diversity would suggest balancing or neutral processes, not a sweep. A random mutation hotspot with neutral effects wouldn’t consistently align with the adaptive plate-reduction pattern seen across populations.