Question 1

Which of the following best describes a plasmid in prokaryotic cells?

Accepted Answer

A small, independently replicating DNA molecule that is usually circular and carries nonessential but often helpful genes.

Question 2

In most Bacteria and Archaea, the main genetic element is:

Accepted Answer

A single circular chromosome containing all or most genes.

Question 3

Which of the following is a key feature that distinguishes plasmids from chromosomes in prokaryotes?

Accepted Answer

Plasmids replicate independently of the host chromosome.

Question 4

A researcher discovers a gene cluster in a bacterial genome that encodes proteins for toxin production and is absent in closely related non-pathogenic strains. This cluster is most likely:

Accepted Answer

A pathogenicity island acquired through horizontal gene transfer.

Question 5

Which of the following best explains why resistance plasmids are a major concern in clinical settings?

Accepted Answer

They can confer resistance to antibiotics and other growth inhibitors, spreading rapidly among bacteria.

Question 6

Horizontal gene transfer is best defined as:

Accepted Answer

The transfer of genetic information between cells that are not in a parent-offspring relationship.

Question 7

Which of the following is a method used to detect horizontal gene transfer in microbial genomes?

Accepted Answer

Identifying regions with significantly different GC content or codon bias compared to the rest of the genome.

Question 8

The pan genome of a microbial species is defined as:

Accepted Answer

All the genes present in all strains of the species, including both core and accessory genes.

Question 9

Which of the following statements about metagenomics is correct?

Accepted Answer

It analyzes pooled DNA or RNA from environmental samples containing organisms that have not been isolated or identified.

Question 10

A patient is infected with a bacterial strain that can attach to host cells and produce toxins, but a closely related strain cannot. What is the most likely explanation for this difference?

Accepted Answer

The pathogenic strain has acquired a plasmid or chromosomal island encoding virulence factors.

Question 11

Which of the following best describes the core genome of a microbial species?

Accepted Answer

The set of genes shared by all strains of the species.

Question 12

Which of the following is NOT a typical function encoded by plasmids?

Accepted Answer

Essential genes for basic cellular survival.

Question 13

A scientist is studying a bacterial population and finds a DNA segment with a GC content of 70%, while the rest of the genome is 50%. What is the most likely explanation?

Accepted Answer

The segment was acquired through horizontal gene transfer.

Question 14

Which of the following statements about bacteriocins is correct?

Accepted Answer

They are proteins encoded on plasmids that inhibit or kill closely related species or strains.

Question 15

Which of the following best explains why plasmid copy number is important in biotechnology applications?

Accepted Answer

A higher copy number increases the yield of plasmid-encoded products, such as recombinant proteins.

Question 16

Which of the following is a real-world consequence of horizontal gene transfer in bacteria?

Accepted Answer

The rapid spread of antibiotic resistance among pathogenic bacteria.

Question 17

A metagenomic study of the human gut reveals a high proportion of Firmicutes compared to Bacteroidetes. This finding is most likely associated with:

Accepted Answer

Increased obesity in humans and mice.

Question 18

Which of the following equations best represents the relationship between the core genome ($G_{core}$), the pan genome ($G_{pan}$), and the accessory genome ($G_{acc}$) of a species?

Accepted Answer

$G_{pan} = G_{core} + G_{acc}$

Question 19

Which of the following is a characteristic of chromosomal islands in bacteria?

Accepted Answer

They contain clusters of genes for specialized functions, often acquired through horizontal gene transfer.

Question 20

A strain of Rhizobia is unable to fix nitrogen unless it acquires a specific plasmid. This is an example of:

Accepted Answer

A nonessential but helpful gene function encoded by a plasmid.

Microbial Genetic Elements: Chromosomes and Plasmids

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