Multiple Choice
Which of the following observations led to Darwin's major inferences about natural selection?
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1. Introduction to Biology
Natural Selection and Evolution
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Which graph best represents directional selection?
A
A bell-shaped curve shifting to the right or left, indicating a change in the mean phenotype
B
A flat line, indicating no change in phenotype frequency
C
A bell-shaped curve becoming narrower around the mean, indicating reduced variation
D
A bell-shaped curve splitting into two peaks, indicating selection for both extremes
Verified step by step guidance1
Understand the concept of directional selection: Directional selection occurs when one extreme phenotype is favored over others, causing the population's mean phenotype to shift in one direction over time.
Analyze the options provided: Each graph represents a different type of selection or population change. For directional selection, the key feature is a shift in the mean phenotype, not a reduction in variation or selection for extremes.
Option 1: A bell-shaped curve shifting to the right or left represents a change in the mean phenotype, which aligns with the definition of directional selection.
Option 2: A flat line indicates no change in phenotype frequency, which does not represent directional selection.
Option 3 and 4: A bell-shaped curve becoming narrower or splitting into two peaks represents stabilizing and disruptive selection, respectively, not directional selection.
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