Which statement best characterizes directional selection?

Which statement best characterizes directional selection?

• A. It increases genetic variation
• B. It shifts the mean phenotype toward one extreme
• C. It increases fitness of individuals near the center
• D. It favors intermediate phenotypes

Answer: (B)

Directional selection occurs when individuals at one end of the phenotypic range have higher fitness than others. Because these individuals leave more offspring, the alleles that produce that extreme value become more common, shifting the population’s mean toward that extreme over generations. The distribution moves in that direction and the trait's variation can diminish if selection is strong. This is different from stabilizing selection, which favors intermediate values and keeps the mean near the center, or disruptive selection, which favors extremes on both ends. An example is the change in moth populations toward darker coloration when environmental conditions favor it.

Directional selection occurs when individuals at one end of the phenotypic range have higher fitness than others. Because these individuals leave more offspring, the alleles that produce that extreme value become more common, shifting the population’s mean toward that extreme over generations. The distribution moves in that direction and the trait's variation can diminish if selection is strong. This is different from stabilizing selection, which favors intermediate values and keeps the mean near the center, or disruptive selection, which favors extremes on both ends. An example is the change in moth populations toward darker coloration when environmental conditions favor it.