Question 1

Which of the following best describes a frameshift mutation and its likely consequence on the resulting protein?

Accepted Answer

An insertion or deletion of one or more base pairs that alters the reading frame, often producing a completely different and nonfunctional amino acid sequence.

Question 2

A patient is diagnosed with a genetic disorder caused by an expansion of trinucleotide repeats in a gene. Which molecular mechanism most likely led to this mutation?

Accepted Answer

Strand slippage during DNA replication, resulting in the re-replication of repeat sequences.

Question 3

Which of the following is a key difference between germ-line and somatic mutations?

Accepted Answer

Germ-line mutations can be passed to the next generation, while somatic mutations cannot.

Question 4

A base-pair substitution changes a codon from UAU (tyrosine) to UAA (stop). What type of mutation is this?

Accepted Answer

Nonsense mutation

Question 5

Which of the following mutagens is most likely to cause a frameshift mutation?

Accepted Answer

Acridine orange

Question 6

A mutation in the consensus sequence of a gene's promoter most likely results in:

Accepted Answer

A change in the timing or amount of transcription of the gene.

Question 7

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 (BER)

Question 8

A researcher exposes E. coli to UV light, resulting in the formation of thymine dimers. Which repair system is used by E. coli to directly reverse this damage using visible light?

Accepted Answer

Photoreactive repair by photolyase

Question 9

Which of the following best explains the result of the Luria-Delbrück fluctuation test in support of the random mutation hypothesis?

Accepted Answer

Different cultures showed great variation in the number of resistant bacteria, indicating mutations occurred randomly before exposure.

Question 10

Which of the following is a likely consequence if the p53 repair pathway is nonfunctional in a human cell?

Accepted Answer

The cell will be unable to pause the cell cycle for DNA repair, increasing the risk of cancer.

Question 11

A base-pair substitution changes a codon from GAA (glutamic acid) to GAG (glutamic acid). What type of mutation is this?

Accepted Answer

Synonymous (silent) mutation

Question 12

Which of the following best describes the action of alkylating agents such as ethyl methanesulfonate (EMS) on DNA?

Accepted Answer

They add bulky side groups to bases, distorting the DNA helix and causing transition mutations.

Question 13

Which repair system in E. coli uses the methylation status of DNA to distinguish the newly synthesized strand from the template strand?

Accepted Answer

Mismatch repair

Question 14

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

Accepted Answer

Blockage of proper 3' mRNA processing, resulting in reduced functional α-globin protein.

Question 15

Which of the following best describes a second-site reversion (suppressor mutation)?

Accepted Answer

A mutation in a different gene that compensates for the original mutation, restoring the wild-type phenotype.

Question 16

Which of the following is a likely outcome if a cryptic splice site is created by a point mutation in an intron?

Accepted Answer

The mRNA will retain additional intronic sequence, potentially leading to a nonfunctional protein.

Question 17

Which of the following best explains why nonhomologous end joining (NHEJ) is considered an error-prone repair mechanism?

Accepted Answer

It often results in the loss or addition of nucleotides at the break site, leading to mutations.

Question 18

Which of the following is the most direct way to repair a thymine dimer in bacteria?

Accepted Answer

Photoreactivation by photolyase

Question 19

A scientist is using the Ames test to evaluate a new chemical. Which result would indicate that the chemical is a mutagen?

Accepted Answer

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

Gene Mutation, DNA Repair, and Homologous Recombination: Study Notes

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