Question 1

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

Accepted Answer

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

Question 2

In the circular chromosome of Escherichia coli K-12, which of the following is true regarding its structure?

Accepted Answer

It is a single, circular DNA molecule with a single origin of replication ($$oriC).$$

Question 3

Which feature distinguishes plasmids from chromosomal DNA in bacteria?

Accepted Answer

Plasmids replicate independently of the host chromosome and often carry nonessential but helpful genes.

Question 4

A researcher discovers a bacterial strain with a plasmid that confers resistance to multiple antibiotics. What type of plasmid is this most likely to be?

Accepted Answer

Resistance plasmid (R plasmid)

Question 5

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

Accepted Answer

Identifying genes with a GC content or codon bias significantly different from the rest of the genome.

Question 6

Which equation best represents the relationship between the pan genome ($$P$$), core genome ($$C$$), and accessory genes ($$A) in a $$microbial species?

Accepted Answer

$$P = C + A$$

Question 7

A pathogenic bacterium is found to have a chromosomal island encoding genes for toxin production. What is the most likely function of this island?

Accepted Answer

It encodes virulence factors that facilitate disease.

Question 8

Which of the following best describes metagenomics?

Accepted Answer

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

Question 9

If a bacterium acquires a plasmid that encodes bacteriocins, what is the likely ecological impact?

Accepted Answer

It will be able to inhibit or kill closely related species or strains.

Question 10

Which of the following statements about horizontal gene transfer is correct?

Accepted Answer

It can cross phylogenetic domain boundaries and is a major source of microbial evolution.

Question 11

A scientist is studying the microbiome of the human gut. Which two bacterial phyla are most abundant in this environment?

Accepted Answer

Bacteroidetes and Firmicutes

Question 12

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

Accepted Answer

Replication of the host chromosome

Question 13

A strain of Rhizobia is unable to fix nitrogen. Which genetic element is most likely missing or defective?

Accepted Answer

Plasmid encoding nitrogen fixation genes

Question 14

Which of the following best explains why plasmid copy number is variable among different plasmids?

Accepted Answer

Plasmids have different replication origins and control mechanisms.

Question 15

A metagenomic study of soil reveals a gene with a codon usage pattern very different from the majority of other genes. What is the most likely explanation?

Accepted Answer

The gene was acquired through horizontal gene transfer.

Question 16

Which of the following is a defining feature of a chromosomal island?

Accepted Answer

It contains clusters of genes for specialized functions, often acquired by horizontal gene transfer.

Question 17

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 includes genes shared by all strains, while the pan genome includes all genes present in any strain.

Question 18

Which of the following is a real-world consequence of the spread of conjugative resistance plasmids among pathogenic bacteria?

Accepted Answer

Increased difficulty in treating infections due to multi-drug resistance.

Question 19

Which of the following best describes the genetic content analyzed in metatranscriptomics?

Accepted Answer

Total RNA transcripts from a microbial community.

Question 20

A hospital isolates a strain of Salmonella with a pathogenicity island. What is the most likely effect of this genetic element?

Accepted Answer

It increases the bacterium's ability to cause disease by encoding virulence factors.

Genetic Elements in Prokaryotes: Chromosomes and Plasmids

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