BI OD 210 GE N E TI CS
C OMPR EHENS I VE R EVI EW EXAMI NAT I ON
Module 5 Exam
Genetics Review
Course Code: BIOD 210
Total Questions: 70
Academic Year: 2026/2027
Duration: 2 Hours
Instructions: Select the Best Answer
AC AD EM I C YEAR 2 02 6/2 02 7
,1. In the DNA double helix, adenine pairs with thymine through how many hydrogen bonds?
A. One hydrogen bond
B. Two hydrogen bonds
C. Three hydrogen bonds
D. Four hydrogen bonds
Correct Answer: B
Rationale: Correct because adenine and thymine form exactly two hydrogen bonds in the DNA double helix, while
guanine and cytosine form three. This matches the standard Watson-Crick base pairing rules.
2. A pea plant heterozygous for tall stem height (Tt) is crossed with a homozygous short plant (tt). What
percentage of the offspring is expected to be tall?
A. 25%
B. 50%
C. 75%
D. 100%
Correct Answer: B
Rationale: Correct because a Tt x tt cross produces a 1:1 genotypic ratio of Tt:tt, meaning 50% of offspring will
display the tall phenotype. This matches the Mendelian monohybrid cross pattern for a heterozygote crossed with
a homozygous recessive.
3. In a population that is in Hardy-Weinberg equilibrium, the frequency of the recessive allele (q) for a trait is
0.3. What is the expected frequency of homozygous dominant individuals?
A. 0.09
B. 0.42
C. 0.49
D. 0.70
Correct Answer: C
Rationale: Correct because p = 1 - q = 1 - 0.3 = 0.7, and the frequency of homozygous dominant individuals
equals p2 = 0.72 = 0.49. This matches the Hardy-Weinberg principle where p2 + 2pq + q2 = 1.
4. When lactose is present and glucose is absent in the growth medium of E. coli, the lac operon is:
A. Fully repressed
B. Partially induced due to catabolite repression
C. Fully activated and transcribing at maximum rate
D. Transcribing but at a basal level only
Correct Answer: C
Rationale: Correct because in the presence of lactose and absence of glucose, allolactose inactivates the lac
repressor and low cAMP levels are reversed by high cAMP-CAP binding to the promoter. This matches the
condition for maximal lac operon transcription.
5. Down syndrome is most commonly caused by which chromosomal abnormality?
A. Translocation between chromosome 14 and 21
B. Trisomy 21 resulting from nondisjunction
C. Monosomy 21
D. Deletion on the long arm of chromosome 21
, Correct Answer: B
Rationale: Correct because approximately 95% of Down syndrome cases result from meiotic nondisjunction
leading to trisomy 21. This matches the most common etiology of this chromosomal disorder.
6. During the polymerase chain reaction (PCR), what is the primary function of the annealing step?
A. To denature the double-stranded DNA template
B. To allow primers to bind to complementary sequences on the template DNA
C. To extend new DNA strands using Taq polymerase
D. To amplify the target DNA exponentially
Correct Answer: B
Rationale: Correct because the annealing step cools the reaction to approximately 55-65 degrees Celsius, enabling
the forward and reverse primers to hydrogen-bond to their complementary sequences on the single-stranded
template. This matches the second step of each PCR cycle.
7. Which of the following best describes the effect of DNA methylation on gene expression?
A. It generally activates gene transcription by opening chromatin structure
B. It generally silences gene transcription by promoting a closed chromatin conformation
C. It has no effect on gene expression
D. It increases translation efficiency of mRNA
Correct Answer: B
Rationale: Correct because DNA methylation at CpG islands in promoter regions recruits methyl-binding
proteins that condense chromatin, preventing transcription factor access. This matches the established role of
DNA methylation in gene silencing.
8. In eukaryotic cells, which RNA polymerase is responsible for transcribing mRNA?
A. RNA polymerase I
B. RNA polymerase II
C. RNA polymerase III
D. RNA polymerase IV
Correct Answer: B
Rationale: Correct because RNA polymerase II transcribes all protein-coding genes into messenger RNA in
eukaryotes. This matches the division of labor among the three eukaryotic RNA polymerases.
9. Cystic fibrosis is caused by mutations in the CFTR gene, which encodes a:
A. Receptor tyrosine kinase
B. Chloride ion channel
C. Structural protein in cilia
D. Transcription factor
Correct Answer: B
Rationale: Correct because the CFTR gene encodes the cystic fibrosis transmembrane conductance regulator,
which functions as an ATP-gated chloride channel. This matches the molecular basis of cystic fibrosis
pathophysiology.
10. In a pedigree analysis, a pattern where affected males pass the trait to all of their daughters and none of
their sons is characteristic of which mode of inheritance?
A. Autosomal dominant
Page 2
C OMPR EHENS I VE R EVI EW EXAMI NAT I ON
Module 5 Exam
Genetics Review
Course Code: BIOD 210
Total Questions: 70
Academic Year: 2026/2027
Duration: 2 Hours
Instructions: Select the Best Answer
AC AD EM I C YEAR 2 02 6/2 02 7
,1. In the DNA double helix, adenine pairs with thymine through how many hydrogen bonds?
A. One hydrogen bond
B. Two hydrogen bonds
C. Three hydrogen bonds
D. Four hydrogen bonds
Correct Answer: B
Rationale: Correct because adenine and thymine form exactly two hydrogen bonds in the DNA double helix, while
guanine and cytosine form three. This matches the standard Watson-Crick base pairing rules.
2. A pea plant heterozygous for tall stem height (Tt) is crossed with a homozygous short plant (tt). What
percentage of the offspring is expected to be tall?
A. 25%
B. 50%
C. 75%
D. 100%
Correct Answer: B
Rationale: Correct because a Tt x tt cross produces a 1:1 genotypic ratio of Tt:tt, meaning 50% of offspring will
display the tall phenotype. This matches the Mendelian monohybrid cross pattern for a heterozygote crossed with
a homozygous recessive.
3. In a population that is in Hardy-Weinberg equilibrium, the frequency of the recessive allele (q) for a trait is
0.3. What is the expected frequency of homozygous dominant individuals?
A. 0.09
B. 0.42
C. 0.49
D. 0.70
Correct Answer: C
Rationale: Correct because p = 1 - q = 1 - 0.3 = 0.7, and the frequency of homozygous dominant individuals
equals p2 = 0.72 = 0.49. This matches the Hardy-Weinberg principle where p2 + 2pq + q2 = 1.
4. When lactose is present and glucose is absent in the growth medium of E. coli, the lac operon is:
A. Fully repressed
B. Partially induced due to catabolite repression
C. Fully activated and transcribing at maximum rate
D. Transcribing but at a basal level only
Correct Answer: C
Rationale: Correct because in the presence of lactose and absence of glucose, allolactose inactivates the lac
repressor and low cAMP levels are reversed by high cAMP-CAP binding to the promoter. This matches the
condition for maximal lac operon transcription.
5. Down syndrome is most commonly caused by which chromosomal abnormality?
A. Translocation between chromosome 14 and 21
B. Trisomy 21 resulting from nondisjunction
C. Monosomy 21
D. Deletion on the long arm of chromosome 21
, Correct Answer: B
Rationale: Correct because approximately 95% of Down syndrome cases result from meiotic nondisjunction
leading to trisomy 21. This matches the most common etiology of this chromosomal disorder.
6. During the polymerase chain reaction (PCR), what is the primary function of the annealing step?
A. To denature the double-stranded DNA template
B. To allow primers to bind to complementary sequences on the template DNA
C. To extend new DNA strands using Taq polymerase
D. To amplify the target DNA exponentially
Correct Answer: B
Rationale: Correct because the annealing step cools the reaction to approximately 55-65 degrees Celsius, enabling
the forward and reverse primers to hydrogen-bond to their complementary sequences on the single-stranded
template. This matches the second step of each PCR cycle.
7. Which of the following best describes the effect of DNA methylation on gene expression?
A. It generally activates gene transcription by opening chromatin structure
B. It generally silences gene transcription by promoting a closed chromatin conformation
C. It has no effect on gene expression
D. It increases translation efficiency of mRNA
Correct Answer: B
Rationale: Correct because DNA methylation at CpG islands in promoter regions recruits methyl-binding
proteins that condense chromatin, preventing transcription factor access. This matches the established role of
DNA methylation in gene silencing.
8. In eukaryotic cells, which RNA polymerase is responsible for transcribing mRNA?
A. RNA polymerase I
B. RNA polymerase II
C. RNA polymerase III
D. RNA polymerase IV
Correct Answer: B
Rationale: Correct because RNA polymerase II transcribes all protein-coding genes into messenger RNA in
eukaryotes. This matches the division of labor among the three eukaryotic RNA polymerases.
9. Cystic fibrosis is caused by mutations in the CFTR gene, which encodes a:
A. Receptor tyrosine kinase
B. Chloride ion channel
C. Structural protein in cilia
D. Transcription factor
Correct Answer: B
Rationale: Correct because the CFTR gene encodes the cystic fibrosis transmembrane conductance regulator,
which functions as an ATP-gated chloride channel. This matches the molecular basis of cystic fibrosis
pathophysiology.
10. In a pedigree analysis, a pattern where affected males pass the trait to all of their daughters and none of
their sons is characteristic of which mode of inheritance?
A. Autosomal dominant
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