DAT Biology Exam 2026 High-Yield
Practice Questions & Verified Answers
1. A mutation in the lac operon's CAP binding site prevents CAP from binding. In the
presence of lactose and absence of glucose, what is the expected transcription level?
A. High transcription
B. Basal transcription
C. No transcription
D. Inducible but lower than wild-type
Answer: B. Basal transcription
Rationale: CAP binding is required for maximal transcription. Without CAP, even with
lactose (inducer) and no glucose (cAMP high), transcription is only basal. High
transcription requires CAP-cAMP activation; no transcription would occur if repressor
bound, but lactose inactivates repressor.
2. In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele
is 0.3. What is the frequency of heterozygous individuals?
A. 0.21
B. 0.42
C. 0.49
D. 0.09
Answer: B. 0.42
Rationale: If q = 0.3, then p = 0.7. Heterozygote frequency = 2pq = 2(0.7)(0.3) = 0.42.
Other values are incorrect calculations: 0.21 is pq, 0.49 is p^2, 0.09 is q^2.
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,3. Which of the following best explains why the sodium-potassium pump is
electrogenic?
A. It moves 3 Na+ out and 2 K+ in, creating a net negative charge inside.
B. It moves 2 Na+ out and 3 K+ in, creating a net positive charge inside.
C. It moves equal numbers of Na+ and K+ but separates charges.
D. It pumps only Na+ out, hyperpolarizing the cell.
Answer: A. It moves 3 Na+ out and 2 K+ in, creating a net negative charge inside.
Rationale: The Na+/K+ ATPase exports 3 Na+ and imports 2 K+, resulting in a net loss of
one positive charge per cycle, contributing to the negative resting membrane potential. This
electrogenic nature is due to the unequal stoichiometry.
4. A researcher treats cells with a drug that inhibits the enzyme responsible for adding
the poly-A tail to mRNA. Which process is most directly affected?
A. Transcription initiation
B. mRNA stability and export
C. Splicing of introns
D. Translation elongation
Answer: B. mRNA stability and export
Rationale: The poly-A tail protects mRNA from degradation and aids in nuclear export and
translation initiation. Inhibition of polyadenylation leads to unstable, poorly exported
mRNA. Splicing and transcription initiation are independent of poly-A addition.
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,5. In a cross between two heterozygous individuals for a trait showing incomplete
dominance, what phenotypic ratio is expected?
A. 1:2:1
B. 3:1
C. 1:1
D. 9:3:3:1
Answer: A. 1:2:1
Rationale: Incomplete dominance results in a third phenotype in heterozygotes, yielding a
1:2:1 ratio of dominant:intermediate:recessive phenotypes. A 3:1 ratio is seen in complete
dominance; 1:1 in a testcross; 9:3:3:1 in dihybrid crosses.
6. A cell is placed in a hypertonic solution. What immediate change occurs in cell
volume and why?
A. Swelling due to water influx
B. Shrinking due to water efflux
C. No change because the membrane is impermeable
D. Swelling due to solute influx
Answer: B. Shrinking due to water efflux
Rationale: In a hypertonic solution, the external solute concentration is higher, causing
water to move out of the cell by osmosis, leading to cell shrinkage (crenation). Swelling
occurs in hypotonic solutions.
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, 7. During which phase of mitosis are sister chromatids separated and pulled to
opposite poles?
A. Prophase
B. Metaphase
C. Anaphase
D. Telophase
Answer: C. Anaphase
Rationale: Anaphase is characterized by the cleavage of cohesin and separation of sister
chromatids, which are pulled to opposite poles by shortening microtubules. Prophase
involves condensation, metaphase alignment, and telophase reformation of nuclei.
8. Which of the following is a key difference between prokaryotic and eukaryotic DNA
replication?
A. Prokaryotes have multiple origins of replication; eukaryotes have one.
B. Eukaryotes have multiple origins; prokaryotes have one.
C. Prokaryotic replication is bidirectional; eukaryotic is unidirectional.
D. Eukaryotes use RNA primers; prokaryotes do not.
Answer: B. Eukaryotes have multiple origins; prokaryotes have one.
Rationale: Eukaryotic chromosomes are linear and large, requiring multiple origins of
replication to complete replication efficiently. Prokaryotes typically have a single circular
chromosome with one origin. Both use RNA primers and bidirectional replication.
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Practice Questions & Verified Answers
1. A mutation in the lac operon's CAP binding site prevents CAP from binding. In the
presence of lactose and absence of glucose, what is the expected transcription level?
A. High transcription
B. Basal transcription
C. No transcription
D. Inducible but lower than wild-type
Answer: B. Basal transcription
Rationale: CAP binding is required for maximal transcription. Without CAP, even with
lactose (inducer) and no glucose (cAMP high), transcription is only basal. High
transcription requires CAP-cAMP activation; no transcription would occur if repressor
bound, but lactose inactivates repressor.
2. In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele
is 0.3. What is the frequency of heterozygous individuals?
A. 0.21
B. 0.42
C. 0.49
D. 0.09
Answer: B. 0.42
Rationale: If q = 0.3, then p = 0.7. Heterozygote frequency = 2pq = 2(0.7)(0.3) = 0.42.
Other values are incorrect calculations: 0.21 is pq, 0.49 is p^2, 0.09 is q^2.
Page 1 of 76
,3. Which of the following best explains why the sodium-potassium pump is
electrogenic?
A. It moves 3 Na+ out and 2 K+ in, creating a net negative charge inside.
B. It moves 2 Na+ out and 3 K+ in, creating a net positive charge inside.
C. It moves equal numbers of Na+ and K+ but separates charges.
D. It pumps only Na+ out, hyperpolarizing the cell.
Answer: A. It moves 3 Na+ out and 2 K+ in, creating a net negative charge inside.
Rationale: The Na+/K+ ATPase exports 3 Na+ and imports 2 K+, resulting in a net loss of
one positive charge per cycle, contributing to the negative resting membrane potential. This
electrogenic nature is due to the unequal stoichiometry.
4. A researcher treats cells with a drug that inhibits the enzyme responsible for adding
the poly-A tail to mRNA. Which process is most directly affected?
A. Transcription initiation
B. mRNA stability and export
C. Splicing of introns
D. Translation elongation
Answer: B. mRNA stability and export
Rationale: The poly-A tail protects mRNA from degradation and aids in nuclear export and
translation initiation. Inhibition of polyadenylation leads to unstable, poorly exported
mRNA. Splicing and transcription initiation are independent of poly-A addition.
Page 2 of 76
,5. In a cross between two heterozygous individuals for a trait showing incomplete
dominance, what phenotypic ratio is expected?
A. 1:2:1
B. 3:1
C. 1:1
D. 9:3:3:1
Answer: A. 1:2:1
Rationale: Incomplete dominance results in a third phenotype in heterozygotes, yielding a
1:2:1 ratio of dominant:intermediate:recessive phenotypes. A 3:1 ratio is seen in complete
dominance; 1:1 in a testcross; 9:3:3:1 in dihybrid crosses.
6. A cell is placed in a hypertonic solution. What immediate change occurs in cell
volume and why?
A. Swelling due to water influx
B. Shrinking due to water efflux
C. No change because the membrane is impermeable
D. Swelling due to solute influx
Answer: B. Shrinking due to water efflux
Rationale: In a hypertonic solution, the external solute concentration is higher, causing
water to move out of the cell by osmosis, leading to cell shrinkage (crenation). Swelling
occurs in hypotonic solutions.
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, 7. During which phase of mitosis are sister chromatids separated and pulled to
opposite poles?
A. Prophase
B. Metaphase
C. Anaphase
D. Telophase
Answer: C. Anaphase
Rationale: Anaphase is characterized by the cleavage of cohesin and separation of sister
chromatids, which are pulled to opposite poles by shortening microtubules. Prophase
involves condensation, metaphase alignment, and telophase reformation of nuclei.
8. Which of the following is a key difference between prokaryotic and eukaryotic DNA
replication?
A. Prokaryotes have multiple origins of replication; eukaryotes have one.
B. Eukaryotes have multiple origins; prokaryotes have one.
C. Prokaryotic replication is bidirectional; eukaryotic is unidirectional.
D. Eukaryotes use RNA primers; prokaryotes do not.
Answer: B. Eukaryotes have multiple origins; prokaryotes have one.
Rationale: Eukaryotic chromosomes are linear and large, requiring multiple origins of
replication to complete replication efficiently. Prokaryotes typically have a single circular
chromosome with one origin. Both use RNA primers and bidirectional replication.
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