A breeder maintains two lines of mice from the same starting population. In Line 1, only the fastest runners (top 10%) are used as parents each generation. In Line 2, breeders choose parents randomly with respect to running speed. Both lines are housed identically. After 15 generations, Line 1 has a higher mean running speed than Line 2. Which statement best accounts for the difference?
- Line 1 mice ran faster because they trained harder after being selected as parents.
- Line 2 mice ran slower because random mating removes alleles for fast running from populations.
- Line 1 had increased frequency of alleles contributing to fast running due to nonrandom breeding. (correct answer)
- Line 2 had more mutations because random breeding increases mutation rates at running genes.
- The difference occurred because populations change traits to match breeder preferences over time.
Explanation: This question assesses the skill of analyzing artificial selection by comparing outcomes in selected versus control lines to isolate selection effects. The correct answer is choice C because Line 1's nonrandom breeding from the fastest 10% increases alleles for fast running, raising mean speed over 15 generations, consistent with the AP Biology concept that artificial selection drives evolutionary change by favoring specific genotypes. The stimulus contrasts Line 1 with randomly bred Line 2 under identical housing, attributing the speed difference to selection pressure. Running speed as a heritable trait demonstrates directional selection's impact. A tempting distractor is choice A, which is incorrect due to the misconception of teleology, suggesting mice train to meet selection criteria rather than inheriting advantageous alleles. To approach similar questions, use control groups to confirm selection's role and predict trait divergence based on breeding methods.