CLEP - Biology Mechanisms of Natural Selection Questions and Answers — Questions and Answers
Question 1: In a population of birds, individuals with very small beaks and individuals with very large beaks are better able to find food than individuals with medium-sized beaks. Over time, this results in a population with a higher frequency of birds with either very small or very large beaks. Which pattern of natural selection does this scenario describe?
- Stabilizing selection
- Directional selection
- Disruptive selection (Correct answer)
- Sexual selection
Correct answer: Disruptive selection
Disruptive selection occurs when extreme phenotypes are favored over intermediate phenotypes. In this case, both very small and very large beaks are advantageous, while medium-sized beaks are selected against, leading to a bimodal distribution of the trait.
Question 2: Which of the following best defines evolutionary 'fitness'?
- The physical strength and health of an individual.
- The ability of an organism to survive and reproduce in its environment. (Correct answer)
- The lifespan of an organism compared to others in its population.
- The complexity of an organism's adaptations.
Correct answer: The ability of an organism to survive and reproduce in its environment.
In an evolutionary context, fitness is not about physical strength but about an organism's reproductive success. The more offspring an organism produces that survive to reproduce themselves, the greater its fitness.
Question 3: A population of peppered moths experiences a change in its environment when industrial pollution causes trees to become darkened with soot. As a result, the frequency of the dark-colored moth phenotype increases, while the light-colored phenotype becomes rare. This is a classic example of:
- Directional selection (Correct answer)
- Genetic drift
- Disruptive selection
- Stabilizing selection
Correct answer: Directional selection
Directional selection occurs when one extreme phenotype is favored, causing the allele frequency to shift over time in the direction of that phenotype. The darkening of the trees gave a survival advantage to the dark-colored moths, leading to an increase in their frequency in the population.
Question 4: A sudden volcanic eruption drastically reduces the size of a beetle population. The surviving beetles have a different allele frequency by chance than the original population. This event is an example of:
- Gene flow
- Natural selection
- The bottleneck effect (Correct answer)
- Sexual selection
Correct answer: The bottleneck effect
The bottleneck effect is a type of genetic drift that occurs when a population's size is severely reduced due to a random event, like a natural disaster. The allele frequencies of the surviving population may be very different from the original population simply due to chance, not because certain traits were selected for.
Question 5: In a stable environment, human babies with an average birth weight are more likely to survive than babies who are born much smaller or much larger. This is an example of what mechanism of natural selection?
- Disruptive selection
- Stabilizing selection (Correct answer)
- Directional selection
- The founder effect
Correct answer: Stabilizing selection
Stabilizing selection favors the intermediate phenotype and selects against extreme variations. In this case, average birth weight is the most advantageous trait for survival, leading to a narrowing of the phenotypic range in the population.
Question 6: Which of the following is NOT a condition required for natural selection to occur?
- Variation in traits within a population.
- Traits that are heritable.
- Differential survival and reproduction.
- A tendency towards perfection in the population. (Correct answer)
Correct answer: A tendency towards perfection in the population.
Natural selection requires variation, heritability, and differential reproductive success. It is a process that leads to adaptation to the current environment, not a drive towards an abstract concept of 'perfection.' Evolution does not have a predetermined goal.
CLEP - Biology Mechanisms of Natural Selection Questions and Answers
In a population of birds, individuals with very small beaks and individuals with very large beaks are better able to find food than individuals with medium-sized beaks.
Over time, this results in a population with a higher frequency of birds with either very small or very large beaks.
Which pattern of natural selection does this scenario describe?