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AP Biology — Unit 7 — Natural Selection: Evolutionary Mechanisms — Drill 29

Drill 29 ·

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About This Drill

AP Biology — Unit 7 — Natural Selection: Evolutionary Mechanisms — Drill 29 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.

Test your understanding of natural selection evidence using a real-world rock pocket mouse case study. Analyze genotype frequency data and owl predation to evaluate claims about directional selection operating in different microhabitats.

Passage

Researchers studying rock pocket mice (Chaetodipus intermedius) in the Sonoran Desert documented coat color variation across two adjacent habitats. In lava flow zones, the substrate is uniformly dark basalt rock. In sandy wash zones, the substrate is pale tan sand. Researchers captured and genotyped mice from both zones over three consecutive years.
The MC1R gene encodes a protein involved in melanin production. Mice carrying at least one dominant allele (M) produce dark (melanic) coats; mice homozygous recessive (mm) produce pale coats. Predation by owls, which hunt by visual contrast, is the primary selective agent in both zones.
Table 1. Observed genotype frequencies in each zone (Year 3, n = 120 per zone).
ZoneMMMmmm
Lava Flow0.470.410.12
Sandy Wash0.090.190.72

In Year 1, the allele frequencies in both zones were approximately equal (M ≈ 0.48, m ≈ 0.52). By Year 3, the zones had diverged substantially.

Questions in This Drill

  1. Based on the data in Table 1, what does the allele frequency shift between Year 1 and Year 3 in the lava flow zone most directly indicate?
  2. In the sandy wash zone, which mice are most likely to survive to reproductive maturity, and why?
  3. A researcher claims: "The divergence in coat color frequencies between the two zones after three years is more consistent with natural selection than genetic drift." Which of the following best evaluates this claim?
  4. If a wall were built between the lava flow and sandy wash zones, completely preventing migration between them, what would be the most likely long-term outcome?
  5. The rock pocket mouse study is often cited as evidence for natural selection acting in observable time. Which feature of the study design most strengthens this interpretation?