Question 1

Catabolic (degradative) plasmids: Plasmids that carry genes encoding enzymes to degrade aromatic compounds, pesticides, or unusual sugars are called what?

Accepted Answer

Introduction / Context: Many bacteria harbor plasmids that expand their metabolic capabilities. Such plasmids confer ecological advantages by allowing the host to utilize otherwise recalcitrant substrates (e.g., xenobiotics), which is crucial in bioremediation and industrial microbiology. Given Data / Assumptions: The plasmids in question encode catabolic enzymes. Examples include degradation of aromatics or pesticides. Terminology distinguishes between fertility (F), virulence, resistance, and metabolic plasmids. Concept / Approach: Correctly classify plasmids by the phenotypes they encode. F factors mediate DNA transfer. Virulence plasmids encode toxins or adherence systems. Metabolic (catabolic) plasmids encode pathways for unusual carbon or energy sources. Step-by-Step Solution: Identify phenotype: degradation of specific compounds.Match phenotype to category: metabolic (catabolic) plasmids.Exclude F (conjugation) and virulence (pathogenicity) classes.Select “Metabolic plasmids.” Verification / Alternative check: Classic catabolic plasmids (e.g., TOL plasmid for toluene/xylene) exemplify this category and are used in environmental cleanup strategies. Why Other Options Are Wrong: F factors: primarily encode transfer functions (tra genes), not catabolism. Virulence plasmids: promote infection, not substrate degradation. “None of these” is wrong because a named class exists. Common Pitfalls: Confusing “metabolic” with “metabolism in general.” Here it specifically refers to plasmid-encoded catabolic pathways for unusual substrates. Final Answer: Metabolic plasmids

Question 2

Plasmid-mediated traits: Which of the following bacterial properties can be plasmid-mediated (choose the most complete answer)?

Accepted Answer

Introduction / Context: Plasmids can carry diverse genes that alter bacterial phenotype. Recognizing plasmid-mediated traits is important in clinical microbiology (antibiotic resistance), food microbiology (fermentation profiles), and pathogenesis (toxins). Given Data / Assumptions: Some sugar fermentation abilities can be plasmid encoded in certain Enterobacteriaceae. Enterotoxin production (e.g., ETEC heat-labile/heat-stable toxins) may be plasmid borne. Antibiotic resistance genes are a classic plasmid-mediated trait (R plasmids). Concept / Approach: Evaluate each listed phenotype and whether it is known to be plasmid-encoded in at least some strains. If all are plausible and documented, “All of these” is the most complete answer. Step-by-Step Solution: Antibiotic resistance: widely plasmid-borne via R determinants.Enterotoxins: plasmid-encoded toxins are common in diarrheagenic E. coli.Lactose fermentation: although often chromosomal, plasmid-borne lactose operons exist in some species.Therefore select “All of these.” Verification / Alternative check: Epidemiological studies of resistance and virulence plasmids confirm plasmid carriage of these traits; plasmid profiling and conjugation experiments demonstrate transferability. Why Other Options Are Wrong: Each single-trait option omits other valid plasmid-mediated traits, making them incomplete. Common Pitfalls: Assuming a trait is never plasmid encoded because it is chromosomal in model strains; plasmid content varies across species and isolates. Final Answer: All of these

Question 3

F factor (fertility plasmid) function: F-factor plasmids primarily mediate which genetic process in bacteria?

Accepted Answer

Introduction / Context: The F (fertility) plasmid is a classic element of bacterial genetics. It encodes the machinery that enables direct DNA transfer between cells. Recognizing its role is essential for understanding how traits spread in populations. Given Data / Assumptions: F factors encode tra genes for pilus formation and DNA transfer. Conjugation requires cell-to-cell contact. The question asks for the primary genetic process mediated by F plasmids. Concept / Approach: Differentiate basic genetic processes: conjugation (DNA transfer via contact), transduction (phage-mediated), and transformation (DNA uptake). F plasmids specifically drive conjugative transfer, occasionally integrating into the chromosome (Hfr) to mobilize chromosomal genes. Step-by-Step Solution: Identify F plasmid components: sex pilus, transfer origin (oriT), tra operon.Link these to conjugation, the direct transfer of DNA.Exclude replication and transcription (general cellular processes), and transduction (phage dependent).Select “Conjugation.” Verification / Alternative check: Hfr mapping experiments demonstrate F-mediated chromosomal gene transfer via conjugation, cementing its central role. Why Other Options Are Wrong: Replication/transcription occur in all cells and are not unique to F plasmids. Transduction is phage-based and independent of F factor. Common Pitfalls: Confusing F with R plasmids; some R plasmids are conjugative, but “F” specifically refers to the fertility factor driving conjugation. Final Answer: Conjugation

Question 4

Horizontal vs. vertical gene transfer — definition: Which statement correctly describes horizontal gene transfer (HGT)?

Accepted Answer

Introduction / Context: Horizontal gene transfer reshapes microbial genomes by introducing new genes outside traditional inheritance. Distinguishing HGT from vertical transmission and basic molecular processes is essential in microbiology and genomics. Given Data / Assumptions: HGT includes transformation, transduction, and conjugation. Vertical transfer is parent-to-progeny inheritance. Central dogma terms (translation and transcription) describe molecular synthesis, not inheritance. Concept / Approach: Choose the option that explicitly states gene flow between mature, non-parental organisms. Exclude definitions that refer to vertical inheritance or molecular synthesis steps. Step-by-Step Solution: Identify HGT: movement of DNA between unrelated cells.Rule out parent-to-offspring (vertical transmission).Rule out translation (protein synthesis) and transcription (RNA synthesis).Select the statement describing inter-organism gene transfer. Verification / Alternative check: Examples include plasmid-mediated antibiotic resistance spread or phage-borne toxin genes, both occurring between mature cells. Why Other Options Are Wrong: Options A and D describe biochemical processes, not inheritance. Option C defines vertical inheritance, not horizontal transfer. Common Pitfalls: Using “horizontal” for any lateral spread including clonal expansion; true HGT requires DNA movement between individuals outside parent–offspring relationships. Final Answer: Transmission of genetic information from one independent, mature organism to another

Question 5

R plasmids terminology: Plasmids that carry both the resistance transfer factor (RTF) and resistance (r) determinants are termed what?

Accepted Answer

Introduction / Context: Antibiotic resistance plasmids (R plasmids) may have two functional parts: an RTF region that mediates transfer and an r-determinant region encoding resistance genes. Terminology distinguishes whether a plasmid can self-transfer. Given Data / Assumptions: RTF provides conjugation (transfer) functions. r determinants encode resistance phenotypes. Presence of both implies self-transmissibility. Concept / Approach: If a plasmid carries both RTF and r determinants, it can transfer itself by conjugation and confer resistance to recipients. Therefore it is a conjugative plasmid. Plasmids lacking transfer functions are non-conjugative and require “helper” plasmids. Step-by-Step Solution: Identify functional modules: RTF (transfer) + r (resistance).Determine capability: can self-transfer via conjugation.Map to term: conjugative plasmid.Select “Conjugative plasmids.” Verification / Alternative check: Mating experiments show such plasmids mobilize themselves and often co-mobilize other plasmids lacking transfer regions if oriT is present. Why Other Options Are Wrong: “Non self-transmissible” and “non-conjugative” contradict the presence of RTF. “None of the above” is incorrect because an established term exists. Common Pitfalls: Confusing conjugative R plasmids with mobilizable plasmids; the latter have oriT but need transfer functions in trans. Final Answer: Conjugative plasmids

Question 6

Recombination without homology used by mobile genetic elements: Which recombination type does not require long homologous sequences and is characteristically used by transposable elements that move about chromosomes?

Accepted Answer

Introduction / Context: Mobile genetic elements move via specialized recombination mechanisms that differ from homologous recombination. Understanding these pathways explains how elements insert broadly and sometimes duplicate themselves during movement. Given Data / Assumptions: Transposable elements can move without long sequence homology. Some transposons use a replicative mechanism, copying the element during transfer. The question targets the mechanism typical of mobile elements roaming chromosomes. Concept / Approach: Two non-homology pathways are commonly discussed: site-specific recombination (used by phage integrases at defined att sites) and replicative recombination (a transposition mechanism where a copy of the element is left behind and another inserts at a new site). The hallmark of many transposons is replicative recombination producing target site duplications and increased copy number. Step-by-Step Solution: Exclude general/homologous recombination; it requires long homology and RecA.Differentiate site-specific integration (phage att) from transposon replication-mediated movement.Associate “mobile elements that move about chromosomes” with transposition via replicative recombination.Select “Replicative recombination.” Verification / Alternative check: Classic models (e.g., Tn3) describe cointegrate formation and resolution, consistent with replicative recombination rather than simple cut-and-paste or att site integration. Why Other Options Are Wrong: Site-specific recombination is more typical of phage integration at specific att sites. “Mutagenic recombination” is not a standard mechanistic category. General recombination needs homology, which contradicts the prompt. Common Pitfalls: Conflating all non-homologous events; transposition often increases copy number (replicative) or moves by cut-and-paste, both distinct from phage att integration. Final Answer: Replicative recombination

Question 7

Specialized vs. generalized transduction: In which form of transduction do transducing particles carry only specific portions of the bacterial genome?

Accepted Answer

Introduction / Context: Transduction is bacteriophage-mediated gene transfer. Different modes (generalized vs. specialized) package bacterial DNA differently. Recognizing which carries specific adjacent genes is essential for mapping and understanding lysogenic conversion. Given Data / Assumptions: Specialized transduction is associated with temperate phages that integrate at defined att sites. Generalized transduction can package random fragments of host DNA following lytic infection. Question asks which carries only specific portions of the bacterial genome. Concept / Approach: When a prophage excises imprecisely, it captures adjacent bacterial genes next to the integration site. Only those loci near the att site are transduced, hence “specialized.” In generalized transduction, headful packaging errors load random host DNA, not limited to a specific site. Step-by-Step Solution: Associate “specific portions adjacent to att” with specialized transduction.Recognize generalized transduction yields random donor loci.Abortive transduction describes non-stable transfer without chromosomal integration, not specificity per se.Select “Specialized transduction.” Verification / Alternative check: Lambda phage integrates at the gal–bio region in E. coli; faulty excision leads to transducing particles carrying only genes adjacent to the att site. Why Other Options Are Wrong: General transduction: random genome fragments. Abortive: DNA persists transiently without full inheritance; not defined by “specific portions.” “None” is invalid because a correct mode is known. Common Pitfalls: Confusing “generalized” with “specialized” due to wording; remember “specialized” equals “specific neighboring genes.” Final Answer: Specialized transduction

Question 8

In microbial genetics, which type of plasmid can exist either autonomously (as an independent circular DNA molecule) or integrated into the host's chromosome, depending on cellular conditions?

Accepted Answer

Introduction / Context: Plasmids are extra-chromosomal, circular DNA molecules that replicate independently in many bacteria. A special category, called episomes, can integrate into the host chromosome and later excise to exist independently. This question checks your understanding of plasmid behavior and vocabulary used in microbial genetics and biotechnology. Given Data / Assumptions: The focus is on a plasmid type that has two lifestyles: free (autonomous) and integrated. The host is a prokaryotic cell (e.g., Escherichia coli). Terms like episome and lysogen have specific meanings in genetics. Concept / Approach: Episomes are plasmids capable of site-specific recombination with the bacterial chromosome. Famous examples include the F factor in E. coli, which can integrate via recombination to form HFr strains, and later excise to become an autonomous F plasmid again. This duality distinguishes episomes from ordinary non-integrative plasmids. Step-by-Step Solution: 1) Identify terms: 'Episome' refers to plasmids that can integrate into the chromosome; 'lysogen' describes a bacterium carrying a prophage (viral genome) integrated into its chromosome.2) Evaluate the options: Medisome and Lisosome are not genetics terms; Lysogen refers to a phage–host state, not a plasmid type.3) Match definition: The only term that matches a plasmid that can exist both integrated and free is 'Episome'. Verification / Alternative check: Recall the F factor behavior: when integrated, the cell is HFr; when excised, the F factor replicates as a plasmid. This is the textbook example of an episome, confirming the choice. Why Other Options Are Wrong: Medisome: Not a standard term in genetics. Lisosome: Misspelling and not a genetics term. Lysogen: Refers to a bacterium carrying a prophage, not a plasmid class. Common Pitfalls: Confusing episomes (plasmid–chromosome integration) with prophages (virus–chromosome integration). Assuming all plasmids can integrate; most cannot without specialized systems. Final Answer: Episome

Question 9

Which transposable element consists of inverted repeat sequences at both ends and carries a gene encoding the transposase enzyme (but no additional cargo genes)?

Accepted Answer

Introduction / Context: Transposable elements are mobile DNA segments. Two common prokaryotic forms are insertion sequences (IS elements) and composite transposons. IS elements are the most minimal units and encode only the functions required for their movement. This question differentiates IS elements from other mobile genetic elements. Given Data / Assumptions: Element has inverted repeats (IRs) at both ends. Element encodes transposase. No mention of extra genes such as antibiotic resistance. Concept / Approach: IS elements include terminal inverted repeats and a transposase gene. Composite transposons consist of two IS elements flanking additional genes (e.g., resistance genes). Viruses and plasmids are broader entities and do not fit the precise structural description of IRs + transposase only. Step-by-Step Solution: 1) Parse the structural features: IRs + transposase = minimal mobile unit.2) Compare to definitions: IS element matches; composite transposon adds cargo genes; virus/plasmid are not defined by IRs + transposase.3) Choose the best match: Insertion element. Verification / Alternative check: Classic examples such as IS1, IS3 families in bacteria have IRs and a transposase, confirming the definition. Why Other Options Are Wrong: Composite transposon: Requires flanking IS elements around additional genes; not minimal. Virus: Encodes viral replication and capsid proteins; not just IRs + transposase. Plasmid: Autonomous circular DNA; lacks the IR/transposase architecture by definition. Common Pitfalls: Assuming all transposons carry resistance genes; IS elements do not. Confusing IRs with palindromic sequences in other contexts. Final Answer: Insertion element

Question 10

In clinical microbiology, which mechanism most commonly explains the emergence of drug resistance in Mycobacterium tuberculosis (tuberculosis)?

Accepted Answer

Introduction / Context: Drug resistance in Mycobacterium tuberculosis has major public health implications. Unlike many other bacteria that frequently exchange resistance genes via mobile elements, M. tuberculosis typically acquires resistance through spontaneous chromosomal mutations selected during inadequate therapy. Given Data / Assumptions: Bacterium: Mycobacterium tuberculosis. Focus: primary cause of resistance acquisition in clinical settings. Horizontal gene transfer is rare in M. tuberculosis populations. Concept / Approach: Resistance to isoniazid, rifampicin, fluoroquinolones, and other agents often maps to point mutations in genes such as katG, inhA promoter, rpoB, and gyrA/gyrB. Selection occurs under suboptimal drug exposure, poor adherence, or monotherapy. This is a classical mutation–selection model rather than plasmid-mediated transfer. Step-by-Step Solution: 1) Identify genetic exchange frequency in M. tuberculosis: extremely low.2) Recall known resistance loci: katG, rpoB, gyrA, rrs, embB.3) Conclude that resistance most often arises via chromosomal mutation followed by selection. Verification / Alternative check: Global surveillance and molecular diagnostics (e.g., rpoB mutation detection by molecular assays) support mutation-driven resistance, confirming the mechanism. Why Other Options Are Wrong: Transduction/Transformation/Conjugation: Horizontal gene transfer mechanisms are not the predominant pathway in M. tuberculosis; plasmids and phage-mediated exchanges are uncommon in clinical strains. Common Pitfalls: Assuming resistance is always plasmid-borne as in Enterobacterales; M. tuberculosis is different. Confusing selection (clinical mismanagement) with mutation origin. Final Answer: Mutation

Question 11

What is the correct term for transfer of genetic material between bacteria that are in direct physical contact via a mating bridge (pilus)?

Accepted Answer

Introduction / Context: Bacteria exchange genes through several mechanisms. Direct, pilus-mediated DNA transfer between two living cells is a hallmark of conjugation. Mastering these terms is crucial in microbial genetics and antimicrobial resistance studies. Given Data / Assumptions: Cells are in direct contact. DNA passes through a conjugative pilus or mating channel. Donor typically carries a conjugative plasmid (e.g., F factor). Concept / Approach: Conjugation requires tra genes that assemble the mating apparatus. DNA is nicked at oriT and transferred as a single strand, then replicated in both donor and recipient. Transformation, by contrast, involves uptake of free DNA from the environment; transduction involves bacteriophages; replication is DNA duplication within a cell. Step-by-Step Solution: 1) Match the condition “direct contact” to the correct mechanism.2) Recall that conjugation uniquely requires cell–cell contact via a pilus.3) Select conjugation as the correct process. Verification / Alternative check: Classic E. coli F+ to F− mating experiments and HFr mapping confirm the definition of conjugation. Why Other Options Are Wrong: Transformation: Involves competent cells taking up naked DNA; no contact needed. Transduction: DNA moved by phage particles, not direct contact. Replication: DNA duplication inside a cell, not gene transfer between cells. Common Pitfalls: Using “lysogeny” or “transduction” interchangeably with conjugation. Forgetting that conjugation typically needs conjugative genes on a plasmid or integrated element. Final Answer: Conjugation

Question 12

Which plasmids do not encode the information required for their own transfer to another cell (i.e., they lack the full set of conjugation genes)?

Accepted Answer

Introduction / Context: Plasmids vary in their ability to move between cells. Conjugative plasmids carry a full set of transfer (tra) genes to build a mating apparatus. Non-conjugative plasmids lack these functions and cannot self-transfer. Recognizing this distinction is essential in molecular cloning and epidemiology of resistance genes. Given Data / Assumptions: The question asks about plasmids that do not self-transfer. Transfer requires a functional set of tra genes and oriT. Concept / Approach: Non-conjugative plasmids can still sometimes be mobilized if a helper conjugative plasmid supplies missing functions in trans, but on their own they cannot initiate transfer. Step-by-Step Solution: 1) Define conjugative vs. non-conjugative based on gene content.2) Choose the category that lacks transfer genes: non-conjugative plasmids. Verification / Alternative check: In lab practice, small cloning plasmids (e.g., many ColE1 derivatives) are non-conjugative unless a helper plasmid is present. Why Other Options Are Wrong: Conjugative plasmids: By definition self-transfer. Cryptic plasmids: Often lack obvious phenotypes, but may or may not have transfer genes; the term does not strictly define transfer ability. None of these: Incorrect because a correct category exists. Common Pitfalls: Equating “cryptic” with “non-conjugative” universally. Forgetting mobilization by helper plasmids does not make a plasmid conjugative. Final Answer: Non-conjugative plasmids

Question 13

What is the principal difference between a self-transmissible (conjugative) plasmid and a mobilizable plasmid?

Accepted Answer

Introduction / Context: Plasmid transfer depends on specialized genes. Conjugative (self-transmissible) plasmids encode the full set of transfer (tra) functions, including pilus formation and DNA processing. Mobilizable plasmids generally contain an origin of transfer (oriT) and relaxase but lack the mating pair formation genes, relying on a helper plasmid for transfer. Given Data / Assumptions: We must compare genetic content required for transfer. Both plasmid types can move under some conditions, but only one supplies all required machinery. Concept / Approach: Self-transmissible plasmids encode both DNA processing and mating pair formation components. Mobilizable plasmids only encode a subset (often relaxase and oriT) and piggyback on a co-resident conjugative plasmid. Step-by-Step Solution: 1) Identify essential functions for conjugation: relaxosome + mating apparatus.2) Assign these to plasmid classes: self-transmissible carry mating apparatus genes; mobilizable do not.3) Choose the option that directly states this difference: “Carries genes encoding the mating apparatus.” Verification / Alternative check: Many IncF and IncP plasmids are self-transmissible. Small cloning plasmids with oriT are mobilizable only in the presence of a helper plasmid. Why Other Options Are Wrong: Transfers both DNA strands: Conjugation typically transfers a single DNA strand; the second strand is synthesized in the recipient. Transfers antibiotic resistance genes: Either plasmid type may carry resistance; this is not the defining difference. Usually has a transposon inserted: Not a defining feature. Common Pitfalls: Confusing oriT presence (mobilizable) with full conjugation capability. Assuming resistance genes imply self-transmissibility. Final Answer: Carries genes encoding the mating apparatus

Question 14

Which term describes the relationship in which a virus persists in a host cell without producing new virions, and the viral genome is replicated along with the host chromosome?

Accepted Answer

Introduction / Context: Bacteriophages can follow lytic or lysogenic cycles. In lysogeny, the phage genome integrates into the bacterial chromosome as a prophage and is replicated passively with the host each cell division. Understanding lysogeny is critical for phage biology and bacterial pathogenicity (lysogenic conversion). Given Data / Assumptions: No new viral particles are produced. Viral genome is replicated with the host chromosome. Direct association with bacteriophage–bacterium systems. Concept / Approach: Lysogeny involves integration (or stable maintenance) of the phage genome and expression of repressor proteins that block lytic genes. The prophage can later be induced (e.g., by DNA damage) to enter the lytic cycle. Step-by-Step Solution: 1) Match features (no virion production, genome co-replication) to phage life cycles.2) Identify lysogeny as the only option matching both features.3) Select “Lysogeny.” Verification / Alternative check: Classic lambda phage model: cI repressor maintains lysogeny; induction leads to lytic replication. Why Other Options Are Wrong: Lysis: Involves active virion production and cell rupture. Transformation/Conjugation: Horizontal gene transfer between bacteria; unrelated to phage persistence. Common Pitfalls: Equating lysogeny with generalized transduction; they are distinct processes. Assuming all integrated elements immediately produce virions—lysogeny is dormant. Final Answer: Lysogeny

Question 15

In bacterial genetics, what term is used for a cell that has gained the physiological state required to take up naked (extracellular) DNA from its environment?

Accepted Answer

Introduction / Context: Transformation is the uptake of free DNA by bacteria. Only cells in a specific physiological state—called competence—can bind, import, and integrate extracellular DNA. Competence may occur naturally (e.g., Streptococcus pneumoniae, Bacillus subtilis) or be induced artificially in the lab (chemical competence or electroporation). Given Data / Assumptions: The question refers to uptake of naked DNA. We focus on the recipient cell's state, not the DNA type. Concept / Approach: Competent cells express surface structures and DNA transport machinery that facilitate binding and translocation of DNA across the membrane(s). Once inside, DNA can recombine with the chromosome or persist as a plasmid (if replication origin is compatible). Step-by-Step Solution: 1) Identify the process: transformation.2) Identify the necessary cellular state: competence.3) Choose the term describing the cell: competent. Verification / Alternative check: Laboratory protocols routinely create competent E. coli cells (e.g., CaCl2 or electroporation), validating the terminology. Why Other Options Are Wrong: Complementary/Liable: Not used in this context. Infected: Refers to phage or pathogen entry, not DNA uptake per se. Common Pitfalls: Confusing competence (state) with competency (general ability); in microbiology, “competent” is standard. Assuming transformation always integrates DNA; plasmids may remain extrachromosomal. Final Answer: Competent

Question 16

In conjugation genetics, chromosomal genes associated with an integrated fertility factor are collectively characteristic of which bacterial state?

Accepted Answer

Introduction / Context: The fertility (F) factor in E. coli can exist as a plasmid or integrate into the chromosome. When the F factor is integrated, the cell is termed HFr (High-frequency recombination) because chromosomal DNA is efficiently transferred during conjugation. This concept is central to classical bacterial mapping. Given Data / Assumptions: F factor is present in association with chromosomal genes. Focus is on the cellular state name. Concept / Approach: HFr cells result from site-specific recombination of the F factor into the chromosome. During mating, transfer begins at oriT in the integrated F, so extensive chromosomal regions can be transferred to the recipient. Step-by-Step Solution: 1) Distinguish F states: F+ (free plasmid), HFr (integrated), F′ (F prime carrying chromosomal genes), R factor (resistance plasmid).2) The prompt states chromosomal genes with fertility factor → HFr.3) Choose HFr. Verification / Alternative check: HFr mapping experiments (minutes map) historically defined gene order by interrupted matings, confirming the definition. Why Other Options Are Wrong: R factor: Resistance plasmids; not necessarily fertility related. F factor: Free, not integrated. F prime factor: F plasmid that excised aberrantly and carries some chromosomal genes; distinct from HFr. Common Pitfalls: Confusing F′ with HFr; F′ is plasmid-borne with extra genes, whereas HFr is integrated. Final Answer: HFr

Question 17

In the lysogenic cycle of a bacteriophage, which statement correctly describes the state of the phage genome with respect to the bacterial host?

Accepted Answer

Introduction / Context: Lysogeny is a dormant relationship between a bacteriophage and its bacterial host. Instead of producing new virions immediately, the phage genome becomes a prophage integrated into the host chromosome and is replicated with the host. This concept underpins lysogenic conversion and prophage induction. Given Data / Assumptions: We focus on the state of the phage genome during lysogeny. No lytic replication occurs during stable maintenance. Concept / Approach: In lysogeny, integration is mediated by phage integrase and host recombination systems. A repressor protein keeps lytic genes inactive. Environmental stress (e.g., DNA damage) can trigger induction to the lytic cycle. Step-by-Step Solution: 1) Identify that lysogeny ≠ active phage production.2) Recognize that the hallmark is chromosomal integration of the phage genome (prophage).3) Select the option describing integration into the bacterial genome. Verification / Alternative check: Lambda phage lysogeny model (cI repressor, att sites) is the classic proof. Why Other Options Are Wrong: Phage transfers bacterial DNA: That is generalized or specialized transduction, not lysogeny itself. Bacteria take up dsDNA from environment: Transformation, not lysogeny. Extracellular DNases stop the process: Relevant to transformation, not to integrated prophage maintenance. Common Pitfalls: Mixing up transduction (DNA transfer by phage particles) with the dormancy of lysogeny. Final Answer: A bacteriophage genome is integrated into the bacterial genome

Question 18

Horizontal gene transfer in bacteria Which process specifically transports bacterial DNA from one bacterium to another by means of bacteriophages (virus-mediated transfer)?

Accepted Answer

Introduction / Context: Bacteria exchange genetic information by several horizontal gene transfer mechanisms. Distinguishing conjugation, transformation, and transduction is essential in microbiology, antimicrobial resistance studies, and biotechnology. This question asks which process uses bacteriophages (bacterial viruses) to shuttle DNA between cells. Given Data / Assumptions: Bacteriophages infect bacteria and can package DNA. The focus is on the mechanism that uses phage particles as vehicles for DNA transfer. Standard definitions of conjugation, transformation, and translation are assumed. Concept / Approach: Transduction = phage-mediated DNA transfer.Conjugation = cell-to-cell contact via pilus and plasmid or chromosomal DNA transfer.Transformation = uptake of naked DNA from the environment.Translation = protein synthesis from mRNA (not a gene transfer method).Transduction occurs as generalized transduction (random host fragments packaged, e.g., P1, P22) or specialized transduction (specific adjacent genes transferred after prophage excision errors, e.g., lambda). Step-by-Step Solution: Identify the key phrase: “via bacteriophages.”Map this phrase to the correct HGT mechanism: transduction.Confirm that other listed processes do not use phage particles. Verification / Alternative check: Classic experiments with phage P22 in Salmonella and P1 in E. coli demonstrate donor DNA markers moving to recipients within phage heads, independent of physical contact, confirming transduction as the correct mechanism. Why Other Options Are Wrong: Conjugation: Requires conjugative pilus and direct contact. Transformation: DNA uptake from the environment; no phage vehicle. Translation: Central dogma step; unrelated to gene transfer. None of the above: Incorrect because transduction exists and is well characterized. Common Pitfalls: Confusing “transduction” with “translation” due to similar spelling. Assuming all gene transfer requires cell contact; phage-mediated transfer does not. Final Answer: Transduction

Question 19

Mapping bacterial genomes In classical genetics, what key information is generated by interrupted mating (Hfr × F−) experiments that stop conjugation at timed intervals?

Accepted Answer

Introduction / Context: Before whole-genome sequencing, geneticists used conjugation-based methods to infer gene order and relative distances on bacterial chromosomes. Interrupted mating of Hfr donors with F− recipients was a pivotal approach to build chromosome maps in organisms like Escherichia coli. Given Data / Assumptions: Hfr strains transfer chromosomal genes to F− cells starting near the integrated F factor. Blender or mechanical shear is used to stop mating at precise times. Selectable markers allow scoring of which donor genes have entered the recipient at each time point. Concept / Approach: Because transfer proceeds linearly with time from the origin of transfer, earlier-entering genes are closer to the origin and later-entering genes are farther. By plotting gene entry times, researchers deduce gene order and construct time-of-entry maps, which convert to map units (minutes) on the circular chromosome. Step-by-Step Solution: Mate Hfr (donor) with F− (recipient) under controlled conditions.Interrupt conjugation at set times (e.g., 5, 10, 15 minutes).Plate on selective media to determine which donor markers have entered.Order genes by first time of appearance to generate a genetic map. Verification / Alternative check: Independent mapping with phage transduction (co-transduction frequencies) and transformation can confirm local gene order, cross-validating interrupted mating maps. Agreement among methods supports the resulting chromosome map. Why Other Options Are Wrong: DNA homology levels: Measured by hybridization or sequence alignment, not by interrupted mating. DNA sequences: Require sequencing technologies, not conjugation timing. Proteomics and metabolite flux: Determined by mass spectrometry or metabolic assays, not mating experiments. Common Pitfalls: Assuming transfer speed equals physical distance directly; maps are relative “minutes,” not base pairs. Ignoring that origin and orientation depend on the integration site of the F factor in each Hfr strain. Final Answer: Bacterial genome maps

Microbial Recombination and Gene Transfer Questions