BIOL 3301 Dauwalder | Meisel Exam 2 |
Questions and Answers | 2026/27 Updated |
100% Correct - UH.
1. In a dihybrid cross between two heterozygous individuals (AaBb), what is the
probability of producing an offspring with the genotype Aabb, assuming independent
assortment?
A. 1/8
B. 1/16
C. 1/4
D. 3/16
Answer: A. 1/8
Rationale: The probability of Aa is 1/2 and bb is 1/4, giving 1/8. Independent assortment
allows multiplication of probabilities. Other options misapply the product rule or confuse
genotype with phenotype ratios.
2. A researcher identifies a noncoding RNA that silences gene expression by recruiting
chromatin-modifying enzymes. Which mechanism is most likely responsible?
A. RNA interference via siRNA
B. Long noncoding RNA (lncRNA) guiding histone methylation
C. microRNA binding to 3' UTR
D. Antisense RNA blocking translation
Answer: B. Long noncoding RNA (lncRNA) guiding histone methylation
Rationale: lncRNAs can recruit chromatin modifiers like PRC2 to methylate histones and
silence genes. siRNA and miRNA primarily affect mRNA stability or translation, and
antisense RNA blocks translation but does not directly modify chromatin.
Page 1 of 76
,3. Which statement correctly describes the consequence of a nonsense mutation in the
middle of a protein-coding gene?
A. It always results in a nonfunctional protein due to premature termination.
B. It may produce a truncated protein that can retain partial function depending on the
location.
C. It causes a frameshift and alters all downstream amino acids.
D. It is typically silent because of codon degeneracy.
Answer: B. It may produce a truncated protein that can retain partial function
depending on the location.
Rationale: Nonsense mutations create premature stop codons, but the truncated protein
may retain some function if the stop occurs late in the gene. Frameshift is caused by
insertions/deletions, and silent mutations do not change the amino acid.
4. In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele
is 0.3. What is the expected frequency of heterozygous individuals?
A. 0.21
B. 0.42
C. 0.49
D. 0.09
Answer: B. 0.42
Rationale: Using p + q = 1, p = 0.7. Heterozygote frequency is 2pq = 2(0.7)(0.3) = 0.42.
Other options incorrectly calculate allele or genotype frequencies.
Page 2 of 76
,5. A student examines a karyotype and observes a Robertsonian translocation
involving chromosomes 14 and 21. What is the most likely clinical consequence for a
carrier?
A. Increased risk of Down syndrome in offspring
B. Development of chronic myeloid leukemia
C. Infertility due to meiotic arrest
D. No phenotypic effect but risk of unbalanced gametes
Answer: A. Increased risk of Down syndrome in offspring
Rationale: Robertsonian translocation carriers can produce gametes with an extra copy of
chromosome 21, leading to translocation Down syndrome. CML is associated with
Philadelphia chromosome, and infertility is less common.
6. Which experimental technique would best determine the binding sites of a
transcription factor across the entire genome?
A. ChIP-seq
B. RNA-seq
C. Western blot
D. qPCR
Answer: A. ChIP-seq
Rationale: ChIP-seq combines chromatin immunoprecipitation with sequencing to map
protein-DNA interactions genome-wide. RNA-seq measures gene expression, Western blot
detects proteins, and qPCR quantifies specific sequences.
Page 3 of 76
, 7. A mutation in a gene encoding a DNA mismatch repair protein leads to a high
frequency of microsatellite instability. Which type of cancer is most strongly
associated with this defect?
A. Lynch syndrome-associated colorectal cancer
B. BRCA1-associated breast cancer
C. Chronic myeloid leukemia
D. Retinoblastoma
Answer: A. Lynch syndrome-associated colorectal cancer
Rationale: Mismatch repair defects cause microsatellite instability and are hallmark of
Lynch syndrome (hereditary nonpolyposis colorectal cancer). BRCA1 is involved in
homologous recombination, CML in translocation, and retinoblastoma in RB1 mutation.
8. In epigenetic regulation, which modification is generally associated with
transcriptional activation?
A. Histone H3 lysine 9 methylation
B. Histone H3 lysine 27 methylation
C. Histone H3 lysine 4 methylation
D. DNA methylation at CpG islands
Answer: C. Histone H3 lysine 4 methylation
Rationale: H3K4 methylation is a mark of active promoters. H3K9 and H3K27 methylation
are repressive, as is CpG island methylation.
Page 4 of 76
Questions and Answers | 2026/27 Updated |
100% Correct - UH.
1. In a dihybrid cross between two heterozygous individuals (AaBb), what is the
probability of producing an offspring with the genotype Aabb, assuming independent
assortment?
A. 1/8
B. 1/16
C. 1/4
D. 3/16
Answer: A. 1/8
Rationale: The probability of Aa is 1/2 and bb is 1/4, giving 1/8. Independent assortment
allows multiplication of probabilities. Other options misapply the product rule or confuse
genotype with phenotype ratios.
2. A researcher identifies a noncoding RNA that silences gene expression by recruiting
chromatin-modifying enzymes. Which mechanism is most likely responsible?
A. RNA interference via siRNA
B. Long noncoding RNA (lncRNA) guiding histone methylation
C. microRNA binding to 3' UTR
D. Antisense RNA blocking translation
Answer: B. Long noncoding RNA (lncRNA) guiding histone methylation
Rationale: lncRNAs can recruit chromatin modifiers like PRC2 to methylate histones and
silence genes. siRNA and miRNA primarily affect mRNA stability or translation, and
antisense RNA blocks translation but does not directly modify chromatin.
Page 1 of 76
,3. Which statement correctly describes the consequence of a nonsense mutation in the
middle of a protein-coding gene?
A. It always results in a nonfunctional protein due to premature termination.
B. It may produce a truncated protein that can retain partial function depending on the
location.
C. It causes a frameshift and alters all downstream amino acids.
D. It is typically silent because of codon degeneracy.
Answer: B. It may produce a truncated protein that can retain partial function
depending on the location.
Rationale: Nonsense mutations create premature stop codons, but the truncated protein
may retain some function if the stop occurs late in the gene. Frameshift is caused by
insertions/deletions, and silent mutations do not change the amino acid.
4. In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele
is 0.3. What is the expected frequency of heterozygous individuals?
A. 0.21
B. 0.42
C. 0.49
D. 0.09
Answer: B. 0.42
Rationale: Using p + q = 1, p = 0.7. Heterozygote frequency is 2pq = 2(0.7)(0.3) = 0.42.
Other options incorrectly calculate allele or genotype frequencies.
Page 2 of 76
,5. A student examines a karyotype and observes a Robertsonian translocation
involving chromosomes 14 and 21. What is the most likely clinical consequence for a
carrier?
A. Increased risk of Down syndrome in offspring
B. Development of chronic myeloid leukemia
C. Infertility due to meiotic arrest
D. No phenotypic effect but risk of unbalanced gametes
Answer: A. Increased risk of Down syndrome in offspring
Rationale: Robertsonian translocation carriers can produce gametes with an extra copy of
chromosome 21, leading to translocation Down syndrome. CML is associated with
Philadelphia chromosome, and infertility is less common.
6. Which experimental technique would best determine the binding sites of a
transcription factor across the entire genome?
A. ChIP-seq
B. RNA-seq
C. Western blot
D. qPCR
Answer: A. ChIP-seq
Rationale: ChIP-seq combines chromatin immunoprecipitation with sequencing to map
protein-DNA interactions genome-wide. RNA-seq measures gene expression, Western blot
detects proteins, and qPCR quantifies specific sequences.
Page 3 of 76
, 7. A mutation in a gene encoding a DNA mismatch repair protein leads to a high
frequency of microsatellite instability. Which type of cancer is most strongly
associated with this defect?
A. Lynch syndrome-associated colorectal cancer
B. BRCA1-associated breast cancer
C. Chronic myeloid leukemia
D. Retinoblastoma
Answer: A. Lynch syndrome-associated colorectal cancer
Rationale: Mismatch repair defects cause microsatellite instability and are hallmark of
Lynch syndrome (hereditary nonpolyposis colorectal cancer). BRCA1 is involved in
homologous recombination, CML in translocation, and retinoblastoma in RB1 mutation.
8. In epigenetic regulation, which modification is generally associated with
transcriptional activation?
A. Histone H3 lysine 9 methylation
B. Histone H3 lysine 27 methylation
C. Histone H3 lysine 4 methylation
D. DNA methylation at CpG islands
Answer: C. Histone H3 lysine 4 methylation
Rationale: H3K4 methylation is a mark of active promoters. H3K9 and H3K27 methylation
are repressive, as is CpG island methylation.
Page 4 of 76
