Figure 21.3
In a very large population,a quantitative trait has the distribution pattern shown in Figure 21.3.If the curve in Figure 21.3 shifts to the left or to the right,there is no gene flow,and the population size consequently increases over successive generations.Which of the following is (are)probably occurring?
A)immigration or emigration only
B)genetic drift only
C)directional selection and adaptation
D)genetic drift and disruptive selection
E)immigration or emigration,directional selection,and adaptation

Question

Figure 21.3
In a very large population,a quantitative trait has the distribution pattern shown in Figure 21.3.If the curve in Figure 21.3 shifts to the left or to the right,there is no gene flow,and the population size consequently increases over successive generations.Which of the following is (are)probably occurring?
A)immigration or emigration only 
B)genetic drift only 
C)directional selection and adaptation 
D)genetic drift and disruptive selection 
E)immigration or emigration,directional selection,and adaptation

Quizplus · Accepted Answer

If the curve shifts to the left or right, it indicates directional selection and adaptation. This means that certain traits are becoming more advantageous and being selected for, which would cause the shift in the distribution pattern. There is no indication of genetic drift or immigration/emigration in the question. Disruptive selection is not a correct answer because it would result in a bimodal distribution, with peaks at both ends of the graph, rather than a unimodal distribution with a shift to one side.

Figure 21.3 In a Very Large Population,a Quantitative Trait Has the Distribution