Question 1

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

Accepted Answer

An insertion or deletion of one or two nucleotides that shifts the reading frame, often resulting in a completely altered and nonfunctional protein.

Question 2

A researcher exposes bacteria to 5-bromouracil. What type of mutation is most likely to occur, and why?

Accepted Answer

A point mutation, because 5-bromouracil is a base analogue that pairs incorrectly during replication.

Question 3

Which DNA repair mechanism is most likely to fix thymine dimers caused by UV light, and what enzyme is directly involved?

Accepted Answer

Photoreactivation; photolyase

Question 4

In the Ames test, what does an increased number of colonies on the test plate (compared to the control) indicate?

Accepted Answer

The chemical tested is likely a mutagen, increasing the rate of back-mutation in the bacteria.

Question 5

Which of the following best distinguishes vertical gene transfer from horizontal gene transfer in bacteria?

Accepted Answer

Horizontal gene transfer involves the transfer of genetic material between cells that are not direct descendants.

Question 6

A bacterium is exposed to ethidium bromide. What type of mutation is most likely to result, and what is the mechanism?

Accepted Answer

Frameshift mutation due to intercalation between base pairs.

Question 7

Which repair mechanism is most likely to correct a mismatch caused by DNA polymerase during replication, and what is the key recognition signal?

Accepted Answer

Mismatch repair; methylation of the parental DNA strand

Question 8

A bacterium is found to be unable to grow on minimal medium lacking tryptophan but grows on complete medium. What type of mutant is this, and how could you isolate it?

Accepted Answer

Auxotroph; by replica plating from complete to selective medium lacking tryptophan

Question 9

Which of the following scenarios best illustrates generalized transduction?

Accepted Answer

A bacteriophage packages random fragments of host DNA and transfers them to a new host cell.

Question 10

Which of the following is a likely outcome of an Hfr × F– conjugation event?

Accepted Answer

The recipient cell receives chromosomal genes from the donor, but usually remains F–.

Question 11

A mutation changes a codon from UAU (tyrosine) to UAA (stop). What type of mutation is this, and what is the likely effect?

Accepted Answer

Nonsense mutation; truncated protein

Question 12

Which of the following best describes the role of RecA protein in homologous recombination?

Accepted Answer

It facilitates strand invasion and exchange between homologous DNA molecules.

Question 13

Which of the following equations best represents the mutation rate per gene per round of replication for spontaneous mutations in bacteria?

Accepted Answer

$$10^{-6} to$$ $$10^{-7}$$

Question 14

Which of the following is a key difference between specialized and generalized transduction?

Accepted Answer

Generalized transduction can transfer any bacterial gene, while specialized transduction transfers only genes adjacent to the prophage.

Question 15

A suppressor mutation restores the wild-type phenotype in a bacterium with a nonsense mutation. Which mechanism best explains this?

Accepted Answer

A second mutation changes the anticodon of a tRNA, allowing it to recognize the stop codon and insert an amino acid.

Question 16

Which of the following best describes the outcome of a silent mutation?

Accepted Answer

The amino acid sequence of the protein is unchanged.

Question 17

Which DNA repair pathway is most likely to be error-prone and used as a last resort when DNA damage is extensive?

Accepted Answer

SOS repair

Question 18

Which of the following best explains why bacteria accumulate mutations more rapidly than eukaryotes?

Accepted Answer

Bacteria have faster growth rates and less efficient DNA repair mechanisms.

Question 19

Which of the following is NOT a possible outcome of horizontal gene transfer in bacteria?

Accepted Answer

Direct inheritance of genes from parent to offspring

Mechanisms of Genetic Variation in Microorganisms

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