Question 1

Which of the following best describes a frameshift mutation, and what is its likely effect on the resulting protein?

Accepted Answer

An insertion or deletion of one or more base pairs, causing a shift in the reading frame and often producing a nonfunctional protein.

Question 2

A mutation changes the codon UAU (tyrosine) to UAA (stop codon). What type of mutation is this, and what is its consequence?

Accepted Answer

Nonsense mutation; translation will terminate prematurely, likely resulting in a truncated protein.

Question 3

Which of the following is a transition mutation?

Accepted Answer

A change from cytosine (C) to thymine (T).

Question 4

Which of the following best explains why UV light is mutagenic to DNA?

Accepted Answer

UV light creates pyrimidine dimers, distorting DNA conformation and interfering with replication.

Question 5

A patient is diagnosed with xeroderma pigmentosum. Which DNA repair pathway is most likely defective in this individual?

Accepted Answer

Nucleotide excision repair

Question 6

Which of the following statements about the Ames test is correct?

Accepted Answer

It uses strains of Salmonella typhimurium to detect reverse mutations, indicating mutagenicity of compounds.

Question 7

Which of the following is an example of a conditional-lethal mutation with medical relevance?

Accepted Answer

A temperature-sensitive influenza virus strain used in vaccines, which replicates at $$32^\circC $$but not at $$37^\circC.$$

Question 8

Which repair mechanism is activated when DNA polymerase proofreading fails to correct a misincorporated nucleotide?

Accepted Answer

Mismatch repair, which detects, cuts, and removes the mismatch, then fills the gap with the correct nucleotide.

Question 9

A mutation in the $$\beta-$$globin gene leads to $$\beta-$$thalassemia. Which type of mutation is most commonly responsible for this disease?

Accepted Answer

Single nucleotide change or small insertions/deletions in the $$\beta-$$globin gene

Question 10

Which of the following is true regarding transposable elements in the human genome?

Accepted Answer

They make up about half of the human genome and can contribute to genetic variability.

Question 11

Which DNA repair pathway is most likely to be activated in response to double-strand breaks during late S or early G2 phase?

Accepted Answer

Homologous recombination repair, which uses a sister chromatid as a template for accurate repair.

Question 12

A mutation changes an AT base pair to a GC base pair. Which process could have caused this mutation?

Accepted Answer

Deamination, where cytosine is converted to uracil or adenine to hypoxanthine, leading to altered base pairing.

Question 13

Which of the following is a characteristic of a neutral mutation?

Accepted Answer

It occurs in coding or noncoding regions and has no effect on the organism's fitness.

Question 14

Which of the following is a correct description of a missense mutation?

Accepted Answer

A mutation that changes a codon to one that codes for a different amino acid.

Question 15

Which of the following mutagens is most likely to cause oxidative damage to DNA?

Accepted Answer

Superoxides ($$O_2$$^-$$), hydroxyl radicals (OH), and hydrogen peroxide (H_2O_2$)

Question 16

Which statement best describes the Luria-Delbrück fluctuation test and its significance?

Accepted Answer

It demonstrated that mutations arise spontaneously and randomly, not in response to environmental changes.

Question 17

Which of the following is true about the SOS repair system in E. coli?

Accepted Answer

It is a last-resort mechanism that allows replication to continue past DNA damage, but is error-prone and can introduce mutations.

Question 18

Which enzyme is responsible for strand discrimination during mismatch repair in bacteria, and what is its role?

Accepted Answer

Adenine methylase; it methylates adenine residues, allowing the repair system to distinguish the newly synthesized (unmethylated) strand.

Question 19

Which of the following is a consequence of transposable element activity in bacteria?

Accepted Answer

Introduction of multiple drug resistance genes into bacterial plasmids, which can then spread to other strains.

Gene Mutation, DNA Repair, and Transposition – Study Notes

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