BIO-1407 Practice Exam 1

Which statement best defines microevolution?

• Random mutations that never affect phenotype
• Developmental changes during an organism’s life
• Changes in climate that alter species ranges
• Heritable allele frequency shifts within a population across generations
• Appearance of new body plans over geologic eras

Answer explanation

Microevolution refers to changes in allele frequencies within a population over successive generations.

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NGSS.HS-LS4-2

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Which process tends to make populations more genetically similar over time?

• Nonrandom mating
• Natural selection
• Genetic drift
• Mutation
• Gene flow

Answer explanation

Gene flow moves alleles between populations, increasing genetic similarity.

In a large, randomly mating population at equilibrium for a gene with two alleles, the frequency of allele A is [p] = 0.6. What is the expected frequency of heterozygotes?

• 0.60
• 0.24
• 0.36
• 0.48
• 0.16

Answer explanation

Use 2pq = 2(0.6)(0.4) = 0.48 to find the heterozygote frequency.

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NGSS.HS-LS3-3

A population of finches experiences a prolonged drought that favors birds with deeper beaks; the trait distribution shifts to a higher mean with similar variance. Which selection mode best explains this change?

• Stabilizing selection
• Frequency‑dependent selection (negative)
• Disruptive selection
• Directional selection
• Balancing selection via heterozygote advantage

Answer explanation

Directional selection causes a shift in the mean phenotype.

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NGSS.HS-LS4-4

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Two insect populations occupy the same meadow, but one mates only at dawn and the other only at dusk. Which barrier most directly limits gene flow?

• Temporal isolation
• Habitat isolation
• Gametic isolation
• Mechanical isolation
• Reduced hybrid fertility

Answer explanation

Temporal isolation separates species based on mating time.

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NGSS.HS-LS4-4

Fossil data show long periods with little morphological change punctuated by brief intervals of rapid divergence among lineages. This pattern is best described as:

• Punctuated equilibrium
• Hardy–Weinberg equilibrium
• Gradualism
• Orthogenesis
• Saltationism within single generations

Answer explanation

Punctuated equilibrium refers to evolutionary bursts interrupting stasis.

Which mechanism most rapidly generates reproductive isolation in flowering plants?

• Founder effect
• Reinforcement after secondary contact
• Sexual selection on floral color
• Polyploidization following hybridization
• Directional selection across a cline

Answer explanation

Polyploidization creates immediate reproductive barriers.

Arrange the following early‑Earth events from earliest to latest: 1. Formation of protocell‑like compartments 2. Abiotic synthesis of organic monomers 3. Emergence of catalytic, self‑replicating RNA 4. Polymerization into macromolecules

• 4, 2, 3, 1
• 2, 1, 4, 3
• 2, 4, 3, 1
• 1, 2, 4, 3
• 2, 4, 1, 3

Answer explanation

Organic monomers form first, then polymers, compartments, and replicating RNA.

Which observation most strongly supports a bacterial origin of mitochondria?

• Location in the cytoplasm
• Abundance in muscle cells
• Presence of cristae
• Double membrane with inner membrane proteins resembling bacterial transporters
• Association with ATP synthase

Answer explanation

Mitochondria have a double membrane with bacterial-like transport proteins.

Layered, dome‑shaped rock structures interpreted as ancient microbial mats are called:

• Coprolites
• Stromatolites
• Varves
• Amber inclusions
• Concretions

Answer explanation

Stromatolites are ancient microbial mats preserved in rock.

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NGSS.MS-ESS2-3