Question 1

Which of the following mechanisms is NOT a source of genetic variation in prokaryotes?

Accepted Answer

Crossing over during meiosis

Question 2

A bacterial cell is exposed to a chemical mutagen that causes deamination of cytosine. What is the most likely result at the DNA sequence level?

Accepted Answer

Cytosine is converted to uracil, leading to a C-G to T-A transition mutation

Question 3

Which of the following best describes the process of bacterial transformation?

Accepted Answer

Uptake of naked DNA from the environment and incorporation into the genome

Question 4

In Griffith’s classic experiment, what was the key finding when heat-killed smooth (S) strain and live rough (R) strain were injected together into mice?

Accepted Answer

The mice died, and live S strain bacteria were recovered, demonstrating transformation

Question 5

Which of the following is a property of conjugative plasmids?

Accepted Answer

They carry genes for sex pili and can transfer themselves to other bacteria

Question 6

A mutation changes a codon from AAA (Lys) to GAA (Glu), and then a second mutation changes it back to AAA. What is this an example of?

Accepted Answer

True reversion

Question 7

Why are double auxotrophs used in bacterial conjugation experiments?

Accepted Answer

To select for prototrophic recombinants that have regained the ability to synthesize both nutrients

Question 8

Which of the following statements about Hfr strains is correct?

Accepted Answer

Hfr strains have the F plasmid integrated into their chromosome

Question 9

A nonsense mutation in a gene is suppressed by a mutation in a tRNA gene. What is the most likely outcome?

Accepted Answer

The stop codon is read as an amino acid, allowing translation to continue

Question 10

Which of the following best explains why the Ames test uses a reverse mutation screen?

Accepted Answer

It allows detection of mutagens by measuring the reversion of auxotrophs to prototrophy

Question 11

Which of the following is a likely effect of a frame shift mutation in a protein-coding gene?

Accepted Answer

The reading frame is altered, potentially changing every amino acid downstream

Question 12

Which of the following is NOT a possible outcome of a mutation?

Accepted Answer

Guaranteed lethality

Question 13

Which of the following best describes the role of the F factor in E. coli conjugation?

Accepted Answer

It allows the formation of sex pili and transfer of DNA

Question 14

A mutation in the operator region of the lac operon prevents LacI repressor binding. What is the expected outcome?

Accepted Answer

The operon will be constitutively expressed

Question 15

Which of the following is a reason why most carcinogens are also mutagens?

Accepted Answer

They cause heritable changes in DNA sequence that can lead to uncontrolled cell growth

Question 16

Which of the following is a property of R plasmids?

Accepted Answer

They confer resistance to antibiotics

Question 17

Which of the following is the best explanation for why E. coli is not naturally competent for transformation?

Accepted Answer

It lacks the specific protein complexes required for DNA uptake

Question 18

Which of the following mutagens acts as a base analog?

Accepted Answer

5-Bromouracil

Question 19

A bacterial cell with a mutation in the CAP binding site of the lac operon will most likely show which phenotype?

Accepted Answer

Reduced transcription of the lac operon even in the presence of lactose

Genetic Variation and Microbial Evolution: Mechanisms and Consequences

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