Question 1

Which of the following statements best describes the main genetic element in prokaryotes?

Accepted Answer

Chromosomes, which are typically single and circular, carrying most or all essential genes.

Question 2

A researcher discovers a DNA molecule in a bacterium that is circular, about 100 kbp in size, and carries genes for antibiotic resistance. Which genetic element is this most likely to be?

Accepted Answer

A resistance plasmid

Question 3

Which of the following is a key feature distinguishing plasmids from chromosomes in bacteria?

Accepted Answer

Plasmids replicate independently of the host chromosome.

Question 4

Which type of horizontal gene transfer is most likely responsible for the acquisition of a pathogenicity island in a bacterial genome?

Accepted Answer

Conjugation between two bacteria

Question 5

A scientist is analyzing the GC content of a bacterial genome and finds a region with significantly different GC content compared to the rest of the genome. What is the most likely explanation for this observation?

Accepted Answer

The region was acquired through horizontal gene transfer.

Question 6

Which of the following best describes the difference between the core genome and the pan genome of a microbial species?

Accepted Answer

The core genome is shared by all strains, while the pan genome includes all genes found in any strain of the species.

Question 7

Which of the following is a function commonly encoded by plasmids in pathogenic bacteria?

Accepted Answer

Virulence factors such as toxin production or attachment ability

Question 8

A bacterium is found to produce bacteriocins that inhibit closely related species. Which genetic element is most likely responsible for encoding these proteins?

Accepted Answer

Plasmid DNA

Question 9

Which equation would you use to calculate the copy number of a plasmid in a bacterial cell if you know the total amount of plasmid DNA ($D_p$) and the amount of chromosomal DNA ($D_c$), assuming each cell has one chromosome?

Accepted Answer

$\frac{D_p}{D_c}$

Question 10

Which of the following best describes metagenomics?

Accepted Answer

The analysis of pooled DNA or RNA from an environmental sample containing many organisms.

Question 11

In a metagenomic study of the human gut, researchers find a higher proportion of Firmicutes compared to Bacteroidetes. What health condition is this most likely associated with?

Accepted Answer

Increased risk of obesity

Question 12

Which of the following is NOT a typical characteristic of a bacterial chromosome?

Accepted Answer

Replicates independently of the cell cycle

Question 13

A Salmonella strain contains a chromosomal island encoding genes for antibiotic resistance. What is the most likely origin of this island?

Accepted Answer

Horizontal gene transfer from another organism

Question 14

Which of the following is a common method for detecting horizontal gene transfer in microbial genomes?

Accepted Answer

Analyzing the GC content and codon bias of DNA regions

Question 15

Which of the following statements about resistance plasmids is TRUE?

Accepted Answer

They confer resistance to antibiotics and other growth inhibitors.

Question 16

Which of the following best explains why plasmid copy number can vary between different plasmids in the same cell?

Accepted Answer

Plasmids have different replication origins and control mechanisms.

Question 17

A researcher is studying Rhizobia and finds that nitrogen fixation is lost when a specific plasmid is removed. What does this indicate about the genetic basis of nitrogen fixation in Rhizobia?

Accepted Answer

Nitrogen fixation genes are encoded on a plasmid.

Question 18

Which of the following is most likely to be found on a pathogenicity island?

Accepted Answer

Genes encoding virulence factors

Question 19

If a gene in a bacterial genome shows a phylogenetic ancestry pattern that differs from the rest of the genome, what is the most likely explanation?

Accepted Answer

The gene was acquired through horizontal gene transfer.

Question 20

Which of the following best describes the role of bacteriocins encoded by plasmids?

Accepted Answer

They inhibit or kill closely related species or strains.

Genetic Elements in Microbes: Chromosomes, Plasmids, and Genomic Diversity

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