Direction selection on plate reduction would typically produce what pattern in the population over time?

Direction selection on plate reduction would typically produce what pattern in the population over time?

• A. Rapid decrease in allele frequency at EDA.
• B. Increasing frequency of alleles reducing plates.
• C. No change.
• D. Random fluctuation only.

Answer: (B)

Directional selection drives allele frequencies in a single direction when a trait becomes more or less advantageous. In freshwater sticklebacks, having fewer plates is favored because it reduces energy costs and suits the local predator and ecological conditions. So alleles that reduce plate number rise in frequency over generations, shifting the population toward more plate-reduced individuals. Over time you’d see the average plate number decline as the plate-reducing alleles become more common. This is different from no change or random drift, which wouldn’t produce a consistent directional shift. It’s not about a rapid, random fluctuation, but a steady increase in the alleles that produce fewer plates as selection continually favors that phenotype.

Directional selection drives allele frequencies in a single direction when a trait becomes more or less advantageous. In freshwater sticklebacks, having fewer plates is favored because it reduces energy costs and suits the local predator and ecological conditions. So alleles that reduce plate number rise in frequency over generations, shifting the population toward more plate-reduced individuals. Over time you’d see the average plate number decline as the plate-reducing alleles become more common.

This is different from no change or random drift, which wouldn’t produce a consistent directional shift. It’s not about a rapid, random fluctuation, but a steady increase in the alleles that produce fewer plates as selection continually favors that phenotype.