ASU BIO182 GENERAL
BIOLOGY II EXAM 2
PRACTICE EXAM
Question 1: A population of beetles varies in shell color from light tan to dark brown.Birds more easily detect the lightest beetles on dark soil, and over generations the population mean becomes darker. Which mode of selection is occurring?
Choices:
1) Stabilizing selection 2) Directional selection 3) Disruptive selection 4) Frequency-dependent selection
Correct Answer: Directional selection
Explanation: Directional selection shifts the population mean toward one extreme because darker beetles have higher survival and reproductive success.Page 1
Question 2: In a plant population, individuals of intermediate height leave more o�spring than either very short or very tall plants. What is the expected evolutionary e�ect?
Choices:
1) The mean will shift toward greater height 2) Phenotypic variance will increase 3) Phenotypic variance will decrease around the intermediate optimum 4) Both extremes will increase in frequency Correct Answer: Phenotypic variance will decrease around the intermediate optimum Explanation: Stabilizing selection favors intermediate phenotypes and removes extremes, typically reducing variation around the optimum.Question 3: A seed-eating bird population has the highest �tness at either very small or very large beak sizes, while intermediate beaks perform poorly. Which pattern is most likely?
Choices:
1) Directional selection 2) Disruptive selection 3) Stabilizing selection 4) Neutral evolution
Correct Answer: Disruptive selection
Explanation: Disruptive selection favors both extremes over intermediate phenotypes and can increase phenotypic variance.Page 2
Question 4: Which statement best de�nes evolutionary �tness in a population?
Choices:
1) The physical strength of an organism 2) The lifespan of an organism regardless of reproduction 3) The relative contribution of viable fertile o�spring to the next generation 4) The ability to survive a single environmental stress Correct Answer: The relative contribution of viable fertile o�spring to the next generation Explanation: Fitness is measured by relative reproductive success, not merely survival, strength, or longevity.Question 5: A trait is strongly correlated with survival but is not heritable. What is the most likely evolutionary outcome under natural selection?
Choices:
1) The trait will necessarily increase each generation 2) The trait will not show a predictable genetic response to selection 3) The trait will immediately become dominant 4) Mutation will stop in the population Correct Answer: The trait will not show a predictable genetic response to selection Explanation: Natural selection can favor a phenotype, but evolutionary change requires heritable variation so that favored di�erences are transmitted to o�spring.Page 3