BIOL 210 Module 6: Genetics - Mutations and
Variation Updated and Latest Questions and
Correct Answers with Rationale
1. Which type of mutation results in the substitution of a single amino acid in a protein?
A. Missense mutation
B. Silent mutation
C. Nonsense mutation
D. Frameshift mutation
Correct Answer: A
Explanation: A missense mutation is a point mutation where a single nucleotide change
results in a codon that codes for a different amino acid. This can alter the protein’s function
depending on the properties of the new amino acid.
2. A mutation that changes a sense codon into a premature stop codon is called a:
A. Missense mutation
B. Neutral mutation
C. Nonsense mutation
D. Silent mutation
Correct Answer: C
Explanation: Nonsense mutations create a premature termination signal, leading to a
shortened (truncated) and usually non-functional protein.
3. Why does a silent mutation not affect the phenotype of an organism?
A. The repair mechanisms always correct it before translation.
B. The mutation occurs in a non-coding region of the DNA.
C. It changes the DNA sequence but not the amino acid sequence due to codon degeneracy.
D. It only occurs in somatic cells, which do not influence the phenotype.
Correct Answer: C
Explanation: Silent mutations take advantage of the redundancy of the genetic code; a
different codon still specifies the same amino acid, leaving the protein unchanged.
4. Which of the following would most likely cause a frameshift mutation?
A. A base substitution
,B. An insertion of a single nucleotide
C. A transversion mutation
D. An inversion of a gene segment
Correct Answer: B
Explanation: Insertions or deletions that are not in multiples of three shift the reading
frame of the mRNA, drastically changing all subsequent amino acids.
5. If a DNA sequence changes from GAA (Glu) to GAG (Glu), what type of mutation has
occurred?
A. Missense
B. Nonsense
C. Silent
D. Deletion
Correct Answer: C
Explanation: Both GAA and GAG code for glutamic acid, so the protein sequence remains
the same, making it a silent mutation.
6. What is the general term for any physical or chemical agent that increases the rate of
mutation?
A. Mutagen
B. Polymerase
C. Intron
D. Allele
Correct Answer: A
Explanation: Mutagens are external agents like UV light, X-rays, or chemicals that interact
with DNA to induce mutations.
7. Which DNA repair mechanism acts immediately during DNA replication to correct base-
pairing errors?
A. DNA polymerase proofreading
B. Base excision repair
C. Homologous recombination
D. Nucleotide excision repair
Correct Answer: A
, Explanation: DNA polymerases have a 3’ to 5’ exonuclease activity that allows them to
remove and replace incorrectly paired bases during synthesis.
8. The mismatch repair (MMR) system must distinguish between the template strand and the
newly synthesized strand. In bacteria, how is this achieved?
A. By detecting acetyl groups on the template strand
B. By the presence of RNA primers
C. By detecting methylation on the template strand
D. By the thickness of the sugar-phosphate backbone
Correct Answer: C
Explanation: In E. coli, the template strand is methylated at GATC sequences. The repair
system recognizes the unmethylated (new) strand to identify which base needs correction.
9. Which repair pathway is specifically used to fix bulky DNA lesions like thymine dimers
caused by UV light?
A. Mismatch repair (MMR)
B. Base excision repair (BER)
C. Nucleotide excision repair (NER)
D. Direct reversal
Correct Answer: C
Explanation: NER removes a short segment of the DNA strand containing the bulky lesion,
and DNA polymerase fills the gap using the undamaged strand as a template.
10. Which enzyme is responsible for the direct reversal of thymine dimers in some organisms
(though not humans)?
A. Photolyase
B. Ligase
C. Helicase
D. Primase
Correct Answer: A
Explanation: Photolyase uses light energy to break the covalent bonds between adjacent
pyrimidines, restoring the original bases without removing them.
11. What type of DNA repair involves the removal of a single damaged base by a glycosylase
enzyme?
A. Nucleotide excision repair
Variation Updated and Latest Questions and
Correct Answers with Rationale
1. Which type of mutation results in the substitution of a single amino acid in a protein?
A. Missense mutation
B. Silent mutation
C. Nonsense mutation
D. Frameshift mutation
Correct Answer: A
Explanation: A missense mutation is a point mutation where a single nucleotide change
results in a codon that codes for a different amino acid. This can alter the protein’s function
depending on the properties of the new amino acid.
2. A mutation that changes a sense codon into a premature stop codon is called a:
A. Missense mutation
B. Neutral mutation
C. Nonsense mutation
D. Silent mutation
Correct Answer: C
Explanation: Nonsense mutations create a premature termination signal, leading to a
shortened (truncated) and usually non-functional protein.
3. Why does a silent mutation not affect the phenotype of an organism?
A. The repair mechanisms always correct it before translation.
B. The mutation occurs in a non-coding region of the DNA.
C. It changes the DNA sequence but not the amino acid sequence due to codon degeneracy.
D. It only occurs in somatic cells, which do not influence the phenotype.
Correct Answer: C
Explanation: Silent mutations take advantage of the redundancy of the genetic code; a
different codon still specifies the same amino acid, leaving the protein unchanged.
4. Which of the following would most likely cause a frameshift mutation?
A. A base substitution
,B. An insertion of a single nucleotide
C. A transversion mutation
D. An inversion of a gene segment
Correct Answer: B
Explanation: Insertions or deletions that are not in multiples of three shift the reading
frame of the mRNA, drastically changing all subsequent amino acids.
5. If a DNA sequence changes from GAA (Glu) to GAG (Glu), what type of mutation has
occurred?
A. Missense
B. Nonsense
C. Silent
D. Deletion
Correct Answer: C
Explanation: Both GAA and GAG code for glutamic acid, so the protein sequence remains
the same, making it a silent mutation.
6. What is the general term for any physical or chemical agent that increases the rate of
mutation?
A. Mutagen
B. Polymerase
C. Intron
D. Allele
Correct Answer: A
Explanation: Mutagens are external agents like UV light, X-rays, or chemicals that interact
with DNA to induce mutations.
7. Which DNA repair mechanism acts immediately during DNA replication to correct base-
pairing errors?
A. DNA polymerase proofreading
B. Base excision repair
C. Homologous recombination
D. Nucleotide excision repair
Correct Answer: A
, Explanation: DNA polymerases have a 3’ to 5’ exonuclease activity that allows them to
remove and replace incorrectly paired bases during synthesis.
8. The mismatch repair (MMR) system must distinguish between the template strand and the
newly synthesized strand. In bacteria, how is this achieved?
A. By detecting acetyl groups on the template strand
B. By the presence of RNA primers
C. By detecting methylation on the template strand
D. By the thickness of the sugar-phosphate backbone
Correct Answer: C
Explanation: In E. coli, the template strand is methylated at GATC sequences. The repair
system recognizes the unmethylated (new) strand to identify which base needs correction.
9. Which repair pathway is specifically used to fix bulky DNA lesions like thymine dimers
caused by UV light?
A. Mismatch repair (MMR)
B. Base excision repair (BER)
C. Nucleotide excision repair (NER)
D. Direct reversal
Correct Answer: C
Explanation: NER removes a short segment of the DNA strand containing the bulky lesion,
and DNA polymerase fills the gap using the undamaged strand as a template.
10. Which enzyme is responsible for the direct reversal of thymine dimers in some organisms
(though not humans)?
A. Photolyase
B. Ligase
C. Helicase
D. Primase
Correct Answer: A
Explanation: Photolyase uses light energy to break the covalent bonds between adjacent
pyrimidines, restoring the original bases without removing them.
11. What type of DNA repair involves the removal of a single damaged base by a glycosylase
enzyme?
A. Nucleotide excision repair
