Question 1

Which of the following best explains why mutation rates at the DNA level are more similar across different organisms than mutation rates at the phenotypic level?

Accepted Answer

Phenotypic mutation rates are influenced by gene size and function, while DNA-level mutation rates reflect the inherent fidelity of DNA replication and repair.

Question 2

A researcher observes that a particular gene has a much higher mutation rate than others in the genome. Which of the following is the most likely explanation?

Accepted Answer

The gene is a mutation hotspot, possibly due to its large size.

Question 3

In the fluctuation test by Luria and Delbrück, which result would have supported the adaptive mutation hypothesis?

Accepted Answer

Approximately equal numbers of resistant colonies in each culture.

Question 4

Which of the following statements about germ-line and somatic mutations is correct?

Accepted Answer

Germ-line mutations can be passed to the next generation, while somatic mutations affect only the individual.

Question 5

A point mutation in the coding region of a gene changes a codon from GAA to GAG, both of which code for glutamic acid. What type of mutation is this?

Accepted Answer

Synonymous (silent) mutation

Question 6

Which of the following best describes a frameshift mutation?

Accepted Answer

A mutation caused by the insertion or deletion of base pairs, altering the reading frame.

Question 7

A mutation in the promoter region of a gene most likely results in which of the following?

Accepted Answer

Altered timing or amount of gene transcription.

Question 8

A base-pair substitution changes a G to an A in the 5' splice site of an intron. What is the most likely consequence?

Accepted Answer

Improper splicing, possibly resulting in retention of the intron in the mature mRNA.

Question 9

Which of the following best describes a cryptic splice site?

Accepted Answer

A new splice site created by mutation that competes with the authentic splice site.

Question 10

A patient with a rare form of anemia is found to have a mutation in the polyadenylation signal of the alpha-globin gene. What is the most likely molecular consequence?

Accepted Answer

Improper 3' processing of mRNA, leading to reduced functional alpha-globin protein.

Question 11

Which of the following is an example of a true reversion?

Accepted Answer

A second mutation within the same codon restores the original wild-type DNA sequence.

Question 12

A trinucleotide repeat expansion disorder is most likely caused by which molecular mechanism?

Accepted Answer

Strand slippage during DNA replication, leading to increased repeat number.

Question 13

Which of the following best describes the action of a nucleotide base analog such as 5-bromodeoxyuridine?

Accepted Answer

It mimics a normal DNA base and can be incorporated during replication, leading to transition mutations.

Question 14

A chemical mutagen that adds a methyl group to guanine, causing it to mispair with thymine, is best classified as which type of agent?

Accepted Answer

Alkylating agent

Question 15

Which of the following best explains why exposure to UV light increases the risk of skin cancer?

Accepted Answer

UV light induces the formation of photoproducts such as thymine dimers, which, if unrepaired, disrupt replication and increase mutation rates.

Question 16

In the Ames test, what result would indicate that a chemical is a potential mutagen?

Accepted Answer

A significant increase in the number of revertant colonies compared to the control.

Question 17

Which DNA repair mechanism is responsible for removing and replacing a single damaged base, such as uracil resulting from cytosine deamination?

Accepted Answer

Base excision repair

Question 18

A patient with a mutation in the p53 gene is at increased risk for cancer. Which of the following best explains the role of p53 in preventing cancer?

Accepted Answer

p53 can pause the cell cycle to allow DNA repair or trigger apoptosis if damage is irreparable.

Question 19

Which of the following best describes the process of mismatch repair in E. coli?

Accepted Answer

MutS recognizes the mismatch, MutL forms a complex with MutS, and MutH cleaves the unmethylated daughter strand at a GATC site.

11. Gene Mutation, DNA Repair, and Homologous Recombination

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