Q: If DNA polymerase III has an error rate of 1 in 100,000 bases, and proofreading improves this rate 100-fold, what is the new error rate?

$$1 \div (100,000 \times 100) = 1 \div 10,000,000$$

Question 1

Which of the following best describes a transversion mutation?

Accepted Answer

A purine is replaced by a pyrimidine or vice versa.

Question 2

A mutation that changes a codon from one that encodes an amino acid to a STOP codon is called:

Accepted Answer

Nonsense mutation

Question 3

Which DNA repair mechanism uses the methylation status of DNA to distinguish the newly synthesized strand from the template strand?

Accepted Answer

Mismatch repair

Question 4

A patient is diagnosed with Huntington disease, which is caused by a CAG repeat expansion. If the normal allele has 20 repeats and the disease allele has 40 repeats, what type of mutation is this?

Accepted Answer

Replication slippage

Question 5

Which of the following mutagens is known to intercalate into DNA and cause insertions or deletions?

Accepted Answer

Acridine orange

Question 6

A mutation that results in the complete loss of gene function is called:

Accepted Answer

Null mutation

Question 7

Which DNA repair mechanism is activated by blue light and directly reverses pyrimidine dimers?

Accepted Answer

Photoreactivation repair

Question 8

If a mutagen causes guanine to pair with thymine instead of cytosine, what type of chemical modification has likely occurred?

Accepted Answer

Alkylation

Question 9

Which repair pathway is most likely to introduce mutations during the repair of double-strand breaks?

Accepted Answer

Non-homologous end joining (NHEJ)

Question 10

A geneticist uses EMS to induce mutations in Drosophila and screens for recessive lethal mutations. Why are balancer chromosomes used in this experiment?

Accepted Answer

To prevent recombination and maintain lethal alleles in heterozygotes

Question 11

Which of the following is a real-world example of a biochemical mutation?

Accepted Answer

Sickle cell anemia

Question 12

A mutation that only expresses its phenotype under certain environmental conditions is called:

Accepted Answer

Conditional mutation

Question 13

Which of the following best describes a 'cut-and-paste' transposon?

Accepted Answer

It excises itself from one location and inserts into another.

Question 14

If DNA polymerase III has an error rate of 1 in 100,000 bases, and proofreading improves this rate 100-fold, what is the new error rate?

Accepted Answer

$$1 \div (100,000 	imes 100) = 1 \div 10,000,000$$

Question 15

Which of the following is NOT a mechanism by which DNA double-strand breaks can occur?

Accepted Answer

Base excision repair

Question 16

A mutation changes the DNA sequence but does not alter the amino acid sequence of the protein. What type of mutation is this?

Accepted Answer

Silent mutation

Question 17

Which repair mechanism is responsible for removing and replacing 'bulky' DNA lesions such as pyrimidine dimers?

Accepted Answer

Nucleotide excision repair (NER)

Question 18

A genetic screen is performed to identify mutants with a specific phenotype. Which of the following is a key step in confirming that two mutants are in different genes?

Accepted Answer

Complementation analysis

Question 19

Which of the following is a consequence of a frameshift mutation?

Accepted Answer

All amino acids downstream of the mutation are altered

Question 20

Which of the following is true about the Ames test?

Accepted Answer

It uses liver enzymes to mimic metabolic activation of chemicals.

Mutation, Transposition, and DNA Repair: Genetics Study Notes

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