Question

which graph best represents directional selection?
graph a: a graph with two peaks (original population, blue) and a single peak (population after selection, red) between them, labeled proportion of individuals on the y - axis and trait value on the x - axis.
graph b: a graph with a peak (original population, red) and a shifted peak (population after selection, blue), labeled proportion of individuals on the y - axis and trait value on the x - axis.
graph c: a graph with a peak (original population, blue) and a peak (population after selection, red) that is slightly shifted, labeled proportion of individuals on the y - axis and trait value on the x - axis.

Explanation:

Step1: Recall directional selection

Directional selection shifts the population's trait distribution towards one extreme. So the graph should show the peak moving in one direction.

Step2: Analyze each graph

• Graph A: Shows a stabilizing or disruptive - like (two peaks to one) but not directional.
• Graph B: The peak of the population after selection shifts to one side (directional shift), matching directional selection.
• Graph C: Shows a stabilizing selection (peak narrows, no directional shift).

Answer:

Graph B