CLEP Biology Mechanisms of Natural Selection 5 — Questions and Answers
Question 1: Co-evolution between a flower and its specific pollinator is driven by:
- Genetic drift in both species simultaneously
- Reciprocal selection pressures between two interacting species (Correct answer)
- Random mutation in one species affecting the other
- Convergent evolution toward similar traits
Correct answer: Reciprocal selection pressures between two interacting species
Co-evolution involves reciprocal evolutionary changes in two or more species that interact closely, each acting as a selection pressure on the other.
Question 2: Antibiotic resistance in bacteria evolving within a single patient's infection is an example of:
- Macroevolution
- Directional selection acting on existing variation (Correct answer)
- Mutation-driven evolution with no selection
- Genetic drift due to small population size
Correct answer: Directional selection acting on existing variation
Antibiotic treatment acts as directional selection, favoring pre-existing resistant bacteria over sensitive ones already present in the population.
Question 3: Which type of reproductive isolation involves hybrid offspring that are sterile?
- Behavioral isolation
- Hybrid inviability
- Hybrid sterility (Correct answer)
- Temporal isolation
Correct answer: Hybrid sterility
Hybrid sterility is a postzygotic barrier where hybrids survive but cannot reproduce, as seen in mules (horse × donkey crosses).
Question 4: The concept of punctuated equilibrium proposes that evolution:
- Occurs at a constant, gradual rate across all lineages
- Occurs in bursts of rapid change followed by long periods of stasis (Correct answer)
- Is driven entirely by random mutation with no selection
- Only occurs during mass extinction events
Correct answer: Occurs in bursts of rapid change followed by long periods of stasis
Punctuated equilibrium, proposed by Gould and Eldredge, suggests species remain relatively unchanged for long periods interrupted by rapid evolutionary change.
Question 5: Frequency-dependent selection occurs when:
- Selection pressure remains constant regardless of phenotype frequencies
- The fitness of a phenotype depends on how common it is in the population (Correct answer)
- Mutation rates change based on population density
- Only rare alleles are acted upon by selection
Correct answer: The fitness of a phenotype depends on how common it is in the population
In frequency-dependent selection, a phenotype's fitness increases when rare (negative frequency-dependence) or when common (positive frequency-dependence).
Question 6: Vestigial structures provide evidence for evolution because they:
- Are fully functional in all species that possess them
- Represent structures that were useful in ancestral species but reduced in descendants (Correct answer)
- Appear only in embryonic stages and disappear before birth
- Are identical across all related species
Correct answer: Represent structures that were useful in ancestral species but reduced in descendants
Vestigial structures are reduced or nonfunctional remnants of structures that had functions in ancestral species, reflecting shared evolutionary history.
Question 7: Which statement correctly describes the relationship between genotype, phenotype, and natural selection?
- Natural selection acts directly on genotype to change allele frequencies
- Natural selection acts on phenotype; if phenotypic differences are heritable, allele frequencies change (Correct answer)
- Phenotype changes cause corresponding immediate genotype changes
- Natural selection acts equally on all genotypes regardless of phenotype
Correct answer: Natural selection acts on phenotype; if phenotypic differences are heritable, allele frequencies change
Natural selection acts on phenotypes; when phenotypic variation is heritable (genetically based), differential survival and reproduction shift allele frequencies over generations.
CLEP Biology Mechanisms of Natural Selection 5
Co-evolution between a flower and its specific pollinator is driven by: