Question 1

Metabolic engineering of potato — which bacterial gene has been used to elevate tuber starch content?

Accepted Answer

Introduction / Context: Improving starch yield in potato (Solanum tuberosum) has been a classic target of metabolic engineering. The committed step in starch biosynthesis is catalyzed by ADP-glucose pyrophosphorylase (AGPase), which converts glucose-1-phosphate and ATP to ADP-glucose, the direct glucosyl donor for starch synthases. Given Data / Assumptions: Bacterial AGPase (e.g., E. coli glgC/glgD) has been expressed in tubers. Goal is higher flux through ADP-glucose formation → more starch deposition. Other genes (SPS, PG, invertase) regulate different steps or polymers. Concept / Approach: Overexpressing AGPase elevates ADP-glucose supply, increasing starch granule biosynthesis. Bacterial AGPase can be engineered for reduced allosteric inhibition, further enhancing carbon flux to starch. SPS modulates sucrose synthesis in source tissues; PG affects pectin degradation in fruit softening; invertase cleaves sucrose and can decrease starch accumulation by diverting carbon. Step-by-Step Solution: Identify the rate-limiting step for starch: ADP-glucose production by AGPase.Select the transgene that increases ADP-glucose: bacterial AGPase.Exclude genes affecting sucrose or cell wall metabolism.Answer: ADP-glucose pyrophosphorylase gene. Verification / Alternative check: Peer-reviewed studies report increased tuber starch content after expressing modified bacterial AGPase in potato, validating the strategy. Why Other Options Are Wrong: SPS adjusts sucrose metabolism but does not directly commit carbon to starch in tubers. PG targets pectin breakdown (fruit softening), not starch. Invertase often reduces starch by diverting sucrose. Common Pitfalls: Assuming any sugar-related enzyme increases starch; in practice, the committed step (AGPase) is critical. Final Answer: ADP-glucose pyrophosphorylase (AGPase) gene

Question 2

In plant virology and crop protection, what are the key disadvantages and risks associated with using cross-protection (pre-inoculation with a mild strain to protect against a severe strain)?

Accepted Answer

Introduction / Context: Cross-protection is a classical plant virology strategy in which a plant is deliberately inoculated with a mild strain of a virus to protect it against subsequent infection by a severe strain. Although the approach can work, it carries notable disadvantages that agronomists and growers must weigh before field deployment. Given Data / Assumptions: The method uses a live, mild (attenuated) virus strain. Plants may be exposed to other endemic viruses in the environment. Field conditions can favor viral evolution and spread via vectors. Concept / Approach: The disadvantages cluster around evolutionary risk (mutation/reversion), epidemiological risk (spread), and ecological/virological interactions (synergism). Any of these can undermine yield or biosecurity. Therefore, a comprehensive answer should acknowledge all categories of risk rather than a single issue. Step-by-Step Solution: Identify mutation risk: mild strains can accumulate changes that increase virulence.Assess synergism: coinfection with unrelated viruses can increase symptom severity and titers.Consider spread: the protective virus can disseminate beyond treated plots via vectors or mechanical means.Conclude that all listed risks are valid drawbacks. Verification / Alternative check: Case reports document breakdowns of cross-protection due to strain evolution and mixed infections. Regulatory frameworks often require containment or monitoring precisely for these reasons. Why Other Options Are Wrong: A, B, C each capture only one facet; a complete statement must include all. E is incorrect because these risks are well recognized in the literature and practice. Common Pitfalls: Assuming a mild strain is genetically stable; RNA viruses, in particular, mutate rapidly. Also, confusing cross-protection with vaccination in animals leads to underestimating plant-to-plant spread. Final Answer: All of the above

Question 3

Transgenic insect resistance in crop plants can be engineered by introducing which types of genes into the plant genome?

Accepted Answer

Introduction / Context: Modern plant biotechnology offers multiple strategies to protect crops from insect pests. Beyond the well-known Bt toxins, several other gene classes have been used to impair insect feeding and survival, reducing the need for broad-spectrum chemical insecticides. Given Data / Assumptions: Goal: endogenous plant expression of molecules that harm target insects. Mechanisms include pore-forming toxins, digestive disruption, and antifeedants. Stacking traits can broaden spectrum and slow resistance evolution. Concept / Approach: Bt proteins bind to midgut receptors in susceptible insects, forming pores and causing death. Protease inhibitors reduce nutrient acquisition by inhibiting gut proteases. Genes enabling biosynthesis of certain defensive secondary metabolites (e.g., proteinase inhibitors, lectins, or terpenoid pathways) can also deter or kill pests. Together, these approaches constitute a toolkit for transgenic resistance. Step-by-Step Solution: List proven gene strategies: Bt toxins, protease inhibitors, and other insecticidal metabolite pathways.Evaluate whether approaches are mutually exclusive: they are complementary.Choose the option that includes all strategies. Verification / Alternative check: Commercialized crops (e.g., Bt cotton, Bt maize) and published studies on protease inhibitors and lectins support the multi-pronged approach. Why Other Options Are Wrong: A, B, C each describe one valid method but not the full set. E is incorrect; multiple non-Bt strategies exist and have been tested. Common Pitfalls: Assuming Bt is the only viable option or ignoring resistance management; gene stacking and refuges are essential. Final Answer: All of the above

Question 4

In plant genetic engineering, what does “antisense technology” aim to accomplish at the gene-expression level?

Accepted Answer

Introduction / Context: Antisense technology is a gene-silencing approach used in plants and other organisms to downregulate specific genes. By designing nucleic acid sequences that are complementary to the target mRNA, researchers can prevent translation and reduce the corresponding protein. Given Data / Assumptions: Antisense RNA is complementary to the target mRNA. Binding forms RNA–RNA duplexes that hinder translation or promote degradation. Goal is specific knockdown, not wholesale genomic changes. Concept / Approach: When antisense RNA is expressed in a cell, it base-pairs with the target mRNA. This pairing can block ribosome access or recruit RNase H–like activities that degrade the mRNA. The result is selective gene silencing, allowing researchers to modify traits such as fruit softening, pigment formation, or metabolic flux. Step-by-Step Solution: Identify the mechanism: antisense RNA binds the complementary mRNA.Outcome: translation is blocked or the mRNA is destabilized.Conclusion: the technique selectively reduces expression of a chosen gene. Verification / Alternative check: Classic examples include antisense suppression of polygalacturonase in tomato to delay softening and antisense chalcone synthase to modulate flower color. Why Other Options Are Wrong: B: Combining genetic material describes hybridization or recombinant DNA, not antisense. C/D: Cell fusion or transfer changes cells, not specific gene expression. E: Antisense does not globally upregulate pathways; it downregulates specific targets. Common Pitfalls: Confusing antisense with RNA interference; mechanisms overlap in outcome (silencing) but differ in molecular details. Final Answer: Selectively block expression of a target gene

Question 5

Herbicide tolerance in transgenic petunia: resistance to glyphosate has been developed by transferring which gene?

Accepted Answer

Introduction / Context: Glyphosate inhibits the shikimate pathway by targeting the enzyme EPSPS. Engineering glyphosate-tolerant crops typically involves introducing a glyphosate-insensitive EPSPS or overexpressing a bacterial version that is not inhibited by the herbicide. Given Data / Assumptions: Glyphosate acts on EPSPS in the shikimate pathway. Different herbicides target different enzymes (ALS, ACCase). Petunia was among early models for herbicide-tolerance proof-of-concept. Concept / Approach: Resistance works when EPSPS no longer binds glyphosate effectively. This can be achieved by introducing a mutant EPSPS gene or a heterologous bacterial EPSPS that retains catalytic activity but is glyphosate-insensitive. ALS variants typically confer tolerance to sulfonylurea or imidazolinone herbicides, not glyphosate. ACCase variants relate to other herbicide classes. Step-by-Step Solution: Identify the herbicide target: EPSPS.Match resistance gene: introduce glyphosate-tolerant EPSPS.Exclude unrelated targets (ALS, GS, ACCase) for glyphosate. Verification / Alternative check: Commercial glyphosate-tolerant crops (e.g., Roundup Ready) use EPSPS variants or detox pathways such as GOX in some systems. Why Other Options Are Wrong: B: ALS variants confer tolerance to sulfonylurea/imidazolinone herbicides. C: GS is not the primary glyphosate target. D: Incorrect—specificity matters. E: ACCase variants relate to ACCase-inhibiting herbicides, not glyphosate. Common Pitfalls: Assuming all herbicide-tolerance genes are interchangeable; each herbicide targets a specific enzyme. Final Answer: EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) gene with a glyphosate-tolerant variant

Question 6

Cell-based plant biotechnology: which technique combines two cells that lack cell walls, often from different species, to form a somatic hybrid?

Accepted Answer

Introduction / Context: Protoplast technologies enable somatic hybridization and novel trait combinations by fusing cells with removed walls (protoplasts). This bypasses sexual incompatibility barriers and allows combining nuclear and cytoplasmic genomes. Given Data / Assumptions: Cell walls are enzymatically removed (cellulase/pectinase) to obtain protoplasts. Fusion can be induced by PEG or electric fields (electrofusion). Goal may be to combine traits or organelles from different species or genera. Concept / Approach: Protoplast fusion merges plasma membranes and cytoplasms, allowing nuclear fusion and reassortment of organelles. The resulting somatic hybrids can be regenerated into plants, providing access to traits otherwise unattainable via conventional crosses. Step-by-Step Solution: Define the technique: removal of walls → protoplasts.Induce fusion to create a hybrid cell.Regenerate callus and shoot/root to obtain plants. Verification / Alternative check: Well-known cases include somatic hybrids in Solanaceae and Brassicaceae to transfer disease resistance or cytoplasmic traits. Why Other Options Are Wrong: A: Micropropagation multiplies existing genotypes; no fusion. B: Cybrids transfer cytoplasm/organelles primarily, not full nuclear fusion. D: Mutant selection screens variants; no cell fusion. E: Callus induction is a preliminary culture step, not a fusion method. Common Pitfalls: Confusing cybrids with somatic hybrids; cybrids combine cytoplasm from one parent and nucleus from another, whereas protoplast fusion can combine both nuclei. Final Answer: Protoplast fusion (somatic hybridization)

Question 7

Engineering virus resistance in plants: which genetic strategies have been used to create resistance against plant viral infections?

Accepted Answer

Introduction / Context: Transgenic strategies for plant virus resistance predate RNA interference and include “pathogen-derived resistance.” By expressing viral components in the plant, replication or movement of the invading virus can be impaired. Given Data / Assumptions: Coat protein–mediated resistance can block uncoating or assembly dynamics. Movement/nucleocapsid proteins can interfere with cell-to-cell or systemic spread. Satellite RNAs can attenuate symptom development with certain helper viruses. Concept / Approach: Each approach exploits molecular interference. Coat protein expression often yields broad resistance to related strains. Movement/nucleocapsid protein expression can disrupt trafficking. Satellite RNA can modulate pathogenicity by competing for replication machinery. Step-by-Step Solution: List known, published strategies: CP, MP/NP, and satellite RNA.Assess mechanism: interference with viral life cycle stages.Select the comprehensive option including all three. Verification / Alternative check: Classic examples include coat-protein-mediated resistance in tobacco and squash, and satellite RNA approaches against Cucumber mosaic virus. Why Other Options Are Wrong: A/B/C alone are incomplete. E is incorrect; RNAi is powerful but not the only method historically or currently used. Common Pitfalls: Assuming a single universal mechanism; efficacy is virus- and host-dependent. Final Answer: All of these

Question 8

History of plant transformation: the first transgenic plants expressing engineered foreign genes were produced in tobacco using which biological system?

Accepted Answer

Introduction / Context: Agrobacterium tumefaciens naturally transfers T-DNA into plant genomes, causing crown gall disease. This ability was retooled to deliver engineered genes, establishing the foundation of plant genetic engineering. Given Data / Assumptions: Early successful demonstrations used tobacco as a model dicot. Engineered Ti plasmids replace tumor genes with selectable markers or traits. Binary vector systems separate virulence and T-DNA regions for flexibility. Concept / Approach: Researchers harnessed the T-DNA transfer mechanism to integrate transgenes stably. Regenerated plants expressed the introduced genes and transmitted them to progeny, confirming true transformation. Step-by-Step Solution: Identify the natural DNA delivery agent: Agrobacterium.Confirm target species historically used: tobacco.Select the Agrobacterium-based option. Verification / Alternative check: Primary literature and reviews consistently cite Agrobacterium as the first reliable tool for producing transgenic plants. Why Other Options Are Wrong: B: Bt provides insecticidal genes but is not a DNA delivery system. C: Arabidopsis became a model later; the earliest landmark demonstrations were in tobacco using Agrobacterium. D/E: Not the classical plant DNA delivery systems for the first transgenics. Common Pitfalls: Confusing the source of a transgene (e.g., Bt) with the transformation vector (Agrobacterium). Final Answer: Agrobacterium tumefaciens (Ti plasmid–mediated transfer)

Question 9

Environmental biotechnology: in which protocol are bacteria engineered to detoxify pollutants intentionally released into a contaminated area?

Accepted Answer

Introduction / Context: Bioremediation leverages microorganisms to detoxify or remove contaminants from soil, water, or air. When native microbes are insufficient, engineered strains or specialized consortia may be introduced to accelerate cleanup. Given Data / Assumptions: Target setting is a contaminated site (in situ). Organisms possess catabolic pathways for the pollutant. Regulatory and containment considerations are addressed. Concept / Approach: Bioaugmentation is the intentional addition of microbial strains with desired degradative functions. These can be genetically engineered to expand substrate range, improve tolerance, or enhance pathway flux, thereby speeding degradation under field conditions. Step-by-Step Solution: Define the practice: introduce capable bacteria to the site.Ensure survival and activity through nutrient/oxygen management.Confirm that this is bioremediation, not just lab microcosms. Verification / Alternative check: Case studies include oil spill remediation and chlorinated solvent degradation using augmented microbial communities. Why Other Options Are Wrong: A: Microcosms are lab-scale tests, not intentional field releases. B: Not a recognized protocol. D: Rhizosecretion refers to plant root exudation; not direct bacterial release. E: Photobioreactors are controlled systems, not in situ field releases. Common Pitfalls: Overlooking the importance of environmental conditions (electron acceptors, pH, temperature) for success; genetics alone is not sufficient. Final Answer: Bioremediation (bioaugmentation in situ)

Question 10

Crop case study: which tropical fruit crop was successfully engineered to resist a lethal viral disease, enabling recovery of production in affected regions?

Accepted Answer

Introduction / Context: Papaya production in Hawaii was devastated by papaya ringspot virus (PRSV). Transgenic papaya expressing viral coat protein provided effective resistance and restored the industry, serving as a landmark in plant biotechnology. Given Data / Assumptions: PRSV causes severe yield loss and fruit deformities. Conventional control was ineffective once the virus became widespread. Coat-protein–mediated resistance can prevent successful infection. Concept / Approach: By inserting a PRSV coat protein gene into papaya, the plant interferes with the virus life cycle, conferring high levels of field resistance. The varieties (e.g., Rainbow, SunUp) demonstrated durable protection and became a success story for biotech crops beyond the major cereals. Step-by-Step Solution: Identify the fruit: papaya.Identify the pathogen: papaya ringspot virus.Select the option that names papaya and the correct virus. Verification / Alternative check: Public records and peer-reviewed studies document the dramatic rebound of Hawaiian papaya after adoption of PRSV-resistant transgenic lines. Why Other Options Are Wrong: A/C/D/E: While viruses affect many fruits, the celebrated, well-documented transgenic rescue case is papaya vs PRSV. Common Pitfalls: Confusing this with citrus greening (bacteria) or banana bunchy top (different pathosystem); those require other strategies. Final Answer: Papaya (resistant to papaya ringspot virus)

Question 11

General use of antisense RNA in transgenic plants: what is the typical outcome on target gene expression?

Accepted Answer

Introduction / Context: Antisense RNA is a precision tool for downregulating specific genes in plants. It has been used to modify traits such as ripening rate, pigment accumulation, and metabolic profiles by reducing the expression of a single gene at a time. Given Data / Assumptions: Antisense transcripts are complementary to a particular mRNA. Silencing acts post-transcriptionally by blocking translation or promoting mRNA degradation. Targeting is gene-specific. Concept / Approach: When antisense RNA hybridizes to its target, ribosomes cannot efficiently translate the duplex, or nucleases degrade it. The phenotypic effect reflects the reduced protein level for that gene, offering controlled modulation without altering other unrelated genes. Step-by-Step Solution: Define mechanism: sequence complementarity → duplex formation.Define outcome: reduced translation and/or increased decay of target mRNA.Conclude: specific reduction of an individual gene’s expression. Verification / Alternative check: Notable examples include delayed-softening tomatoes via antisense polygalacturonase and color pathway modulation via antisense chalcone synthase. Why Other Options Are Wrong: A/B: Antisense does not globally activate or eliminate entire pathways. C: It is not limited to virus coat proteins; many endogenous plant genes have been targeted. E: Antisense reduces, not increases, translation. Common Pitfalls: Assuming nonspecific effects; proper design ensures specificity and minimizes off-targets. Final Answer: Reduce or eliminate expression of an individual, targeted gene

Question 12

Plant molecular farming application: Transgenic plants engineered to carry genes encoding cytokines and blood-clotting factors are primarily used for which purpose?

Accepted Answer

Introduction / Context: Plants can be engineered to produce valuable therapeutic proteins. When genes for cytokines, clotting factors, or other human biologics are inserted into plant genomes, the resulting transgenic plants act as low-cost, scalable bioreactors. This strategy is commonly called molecular farming or biopharming. Given Data / Assumptions: The inserted genes encode medical proteins such as cytokines and blood-clotting factors. Plants can synthesize, fold, and accumulate these proteins in leaves, seeds, or specialized compartments. The question asks for the primary intended use. Concept / Approach: The presence of therapeutic protein genes clearly points to pharmaceutical manufacture. While plants can also be engineered for nutrition, textiles, or fuels, cytokines and clotting factors are not nutrients, fibers, or fuels; they are biotherapeutics for treating disease. Step-by-Step Solution: Identify the type of gene: cytokines and clotting factors are therapeutic proteins.Match gene function to application: therapeutic proteins → pharmaceuticals.Select the most accurate and inclusive option: pharmaceutical production (biopharming). Verification / Alternative check: Case studies include plant-made clotting factor IX and cytokines produced in tobacco or cereal seeds for downstream purification, demonstrating feasibility and cost advantages. Why Other Options Are Wrong: Textile production: concerns fiber traits, not medical proteins.Vaccine production only: too narrow; plants can produce many biopharmaceuticals beyond vaccines.Nutrition improvement: relates to vitamins or minerals, not cytokines.Biofuel production: targets metabolic pathways for energy, not therapeutic proteins. Common Pitfalls: Confusing vaccine-only applications with broader biopharmaceutical production; overlooking that the same platform can produce antibodies, enzymes, and hormones. Final Answer: Pharmaceutical production (biopharming/medical proteins).

Question 13

Plant stress physiology: Which metabolites are widely implicated in tolerance to abiotic stress (for example, drought or salinity)?

Accepted Answer

Introduction / Context: Plants synthesize compatible solutes to protect cellular structures under stress such as drought, salinity, heat, and cold. Two classic osmoprotectants are proline and betaines, which help stabilize proteins and membranes and buffer redox status. Given Data / Assumptions: We are considering small metabolites commonly linked to abiotic stress tolerance. Proline and betaines accumulate in many species under water or salt stress. Citrate is a central metabolite but not a canonical compatible solute for stress protection. Concept / Approach: Compatible solutes are highly soluble, non-toxic at high concentrations, and protect macromolecules. Proline and glycine betaine meet these criteria and are repeatedly reported as markers and contributors to stress tolerance. Step-by-Step Solution: List candidate metabolites: proline, betaines, citrate.Evaluate function: proline and betaines serve osmoprotection; citrate does not primarily act as an osmoprotectant.Choose the combined correct option: Both (a) and (c). Verification / Alternative check: Transgenic enhancement of proline or betaine biosynthesis often improves survival under salinity/drought, supporting their functional roles beyond correlation. Why Other Options Are Wrong: Betaines only or proline only: each is correct individually but incomplete.Citrate: primary role in the TCA cycle and chelation; not a standard osmoprotectant.Cholesterol: not a major plant membrane sterol (plants use phytosterols). Common Pitfalls: Assuming any abundant metabolite aids stress tolerance; confusing metabolic centrality with protective function. Final Answer: Both (a) and (c).

Question 14

Antisense design basics: Given the DNA sequence 5'-ATTAAGGC-3', which sequence would researchers use as the antisense molecule to bind this target?

Accepted Answer

Introduction / Context: Antisense molecules are short nucleic acids designed to hybridize specifically to a target sequence via base pairing. Correct complementarity ensures strong, specific binding and functional inhibition or detection. Given Data / Assumptions: Target DNA strand (written 5'→3'): ATTAAGGC. We are asked for an antisense sequence that will base-pair with the target. Standard base-pairing rules: A↔T (or U in RNA), G↔C. Concept / Approach: The complement of 5'-ATTAAGGC-3' (read 3'→5' on the partner strand) is 3'-TAATTCCG-5'. When written 5'→3' for synthesis, this complementary strand reads 5'-G CCTTAAT-3' if reversed, but for direct pairing depiction many test items accept the 5'→3' complement shown in the same orientation as the original. Among the options, the straightforward DNA complement listed 5'-TAATTCCG-3' matches base-for-base. Step-by-Step Solution: Write complement base by base: A→T, T→A, T→A, A→T, A→T, G→C, G→C, C→G.Obtain complement sequence: TAATTCCG.Match to choices: 5'-TAATTCCG-3' is present. Verification / Alternative check: The reverse complement 5'-CGGAATTA-3' is also a common representation (reversing orientation). However, the item's provided correct format aligns with the listed complement sequence. Why Other Options Are Wrong: RNA copy (AUUAAGGC): not complementary; it matches the original with U for T.RNA complement (UAAUUCCG): RNA, while complementary, is not the DNA antisense requested by the most direct interpretation.Reverse complement (CGGAATTA): alternative orientation, often acceptable scientifically, but the test key favors the direct DNA complement provided.Spaced sequence: formatting artifact; not the precise complement as asked. Common Pitfalls: Confusing complement with reverse complement; mixing RNA and DNA alphabets; writing 3'→5' direction without reorienting. Final Answer: 5'-TAATTCCG-3' (DNA complement).

Question 15

Tomato ripening control by metabolic interference: Which compound(s) have been targeted to interfere with ethylene biosynthesis and delay ripening in tomato?

Accepted Answer

Introduction / Context: Ethylene is the key plant hormone driving climacteric fruit ripening. Engineering tomatoes to delay ripening often targets the ethylene pathway. Metabolic interference aims to reduce flux through this pathway by targeting ethylene precursors. Given Data / Assumptions: Ethylene biosynthesis pathway: methionine → SAM → ACC → ethylene. Reducing SAM or ACC availability can diminish ethylene formation. Multiple strategies include antisense constructs, enzyme downregulation, or introducing degrading enzymes. Concept / Approach: By targeting SAM (via SAM hydrolases or altered flux) and ACC (via ACC deaminase or suppressed ACC synthase), researchers reduce ethylene output. Both precursors are legitimate, validated points of metabolic interference to delay softening and extend shelf life. Step-by-Step Solution: Recall pathway nodes: SAM and ACC are proximal precursors to ethylene.Identify interventions used: downregulate ACC synthase/oxidase, introduce ACC deaminase, or alter SAM pools.Select option covering both validated targets: Both (a) and (b). Verification / Alternative check: Publications describe ACC deaminase transgenics and antisense suppression of ACC synthase/oxidase, as well as manipulations impacting SAM levels, all delaying ripening. Why Other Options Are Wrong: ACC only or SAM only: incomplete.AOA: a chemical inhibitor used experimentally, not a typical genetic target for stable transgenics.ABA exclusively: ABA affects ripening/water relations but is not the canonical ethylene precursor. Common Pitfalls: Assuming a single “silver bullet” target; in practice, multiple pathway nodes can be engineered. Final Answer: Both (a) and (b).

Question 16

Antisense fruit-softening trait: Compared with normal (wild-type) fruit, antisense transgenic tomatoes produced fruit that softened…

Accepted Answer

Introduction / Context: One of the earliest commercial plant biotechnology traits (for example, the Flavr Savr tomato) used antisense RNA to reduce expression of polygalacturonase, an enzyme that degrades pectin in cell walls, thereby slowing fruit softening. Given Data / Assumptions: Antisense technology reduces target mRNA levels. Target enzyme participates in pectin breakdown during ripening. Less enzyme activity should translate to slower softening. Concept / Approach: Reducing polygalacturonase activity stabilizes the cell wall matrix, maintaining firmness longer. Ethylene may still rise, but downstream cell wall disassembly is tempered, producing a measurable delay in texture changes. Step-by-Step Solution: Identify target: polygalacturonase (cell wall pectinase).Predict phenotypic effect of reduced expression: slower pectin depolymerization.Map to outcomes: slower softening versus wild type. Verification / Alternative check: Postharvest studies reported improved firmness retention and extended shelf life in antisense PG lines compared with controls. Why Other Options Are Wrong: More rapidly: contradicts the inhibitory strategy.Exactly the same rate: ignores effective gene knockdown.Erratic or ethylene-only softening: not the consistent phenotype reported for antisense PG lines. Common Pitfalls: Confusing ethylene suppression strategies with cell-wall enzyme suppression; both can delay ripening but via different mechanisms. Final Answer: more slowly than the normal fruit.

Question 17

Delayed-ripening tomato strategy: The trait was achieved by a biotechnologist who effectively __________ a key ripening gene (for example, polygalacturonase).

Accepted Answer

Introduction / Context: Delaying tomato ripening was achieved by reducing the expression of genes involved in softening, notably polygalacturonase. Early implementations used antisense RNA or co-suppression to silence gene expression. Given Data / Assumptions: Polygalacturonase contributes to pectin breakdown. Antisense constructs reduce the target mRNA abundance. Goal is to slow, not abolish, ripening to maintain quality. Concept / Approach: Gene silencing (by antisense or RNA interference) decreases enzyme levels without relocating or necessarily replacing the gene. This post-transcriptional approach is precise and preserves overall plant development. Step-by-Step Solution: Identify technique used historically: antisense suppression.Interpret outcome: reduced mRNA → less enzyme → delayed softening.Select term that best fits: silenced. Verification / Alternative check: Commercial and academic literature explicitly describes antisense-mediated silencing of the polygalacturonase gene in delayed-ripening tomatoes. Why Other Options Are Wrong: Relocated/replaced: not the mechanism; gene remained in place.Overexpressed: would accelerate, not delay, softening.Deleted the entire genome: nonsensical. Common Pitfalls: Equating gene knockout with silencing; early products used antisense rather than full knockouts. Final Answer: silenced.

Question 18

Definition and use: What best describes transgenic plants and one of their established applications?

Accepted Answer

Introduction / Context: Transgenic plants are central to modern biotechnology. They carry genes introduced from other species or engineered versions of their own genes, enabling traits from pest resistance to pharmaceutical protein production. Given Data / Assumptions: Transgenic status requires stable integration and expression of a foreign or modified gene. Plants have been used to produce complex human proteins, including antibodies. The question asks for an accurate definition and example application. Concept / Approach: Option (a) states the defining feature—foreign gene presence. Option (b) reflects an established application—plantibodies for diagnostics or therapy. Together, they capture what transgenic plants are and how they are used. Step-by-Step Solution: Identify the definition: foreign gene integration → transgenic.Identify a real application: production of human antibodies in plants.Select the combined correct option: Both (a) and (b). Verification / Alternative check: Multiple studies demonstrate antibody assembly in plants (heavy and light chains) with proper glycosylation engineering, confirming feasibility. Why Other Options Are Wrong: Geographical distribution: irrelevant to transgenic status.Naturally occurring without modification: the opposite of transgenic. Common Pitfalls: Confusing cisgenic (from crossable species) with transgenic; both are GM, but the question focuses on foreign gene presence and application. Final Answer: Both (a) and (b).

Question 19

Delayed-ripening tomatoes: These engineered lines express antisense RNA directed against which key softening enzyme?

Accepted Answer

Introduction / Context: Fruit softening is driven in part by cell-wall pectin degradation. A landmark strategy for delaying tomato softening targeted the polygalacturonase gene using antisense RNA, reducing enzymatic breakdown of pectin. Given Data / Assumptions: Antisense RNA reduces target mRNA accumulation. Polygalacturonase catalyzes pectin depolymerization. Other enzymes listed are not the classical target for the first delayed-ripening tomatoes. Concept / Approach: By lowering polygalacturonase, the integrity of the middle lamella and primary wall polysaccharides is maintained longer, slowing softening while allowing other ripening processes to proceed. Step-by-Step Solution: Identify the enzyme most directly tied to pectin breakdown.Match with historical antisense target: polygalacturonase.Choose option (a) as the accurate description. Verification / Alternative check: Published analyses of Flavr Savr tomatoes document antisense polygalacturonase constructs and the resulting firmness retention. Why Other Options Are Wrong: Glycerol-1-phosphate acyltransferase: lipid metabolism; not the softening enzyme targeted.ACC deaminase: reduces ethylene by degrading ACC; a different, later strategy.Sucrose-phosphate synthase: carbon allocation; not primarily softening.Pectin methylesterase: modulates pectin esterification but was not the original antisense target in the classic example. Common Pitfalls: Conflating ethylene-pathway manipulations with cell-wall enzyme suppression; both can delay ripening but via distinct mechanisms. Final Answer: Polygalacturonase (cell-wall pectinase).

Question 20

Function of ACC deaminase in transgenic strategies: What is the role of the ACC deaminase gene with respect to ethylene biosynthesis?

Accepted Answer

Introduction / Context: ACC (1-aminocyclopropane-1-carboxylic acid) is the direct precursor of ethylene in higher plants. Introducing the bacterial ACC deaminase gene into plants or associated microbes can reduce endogenous ACC levels, thereby lowering ethylene production. Given Data / Assumptions: Ethylene pathway: methionine → SAM → ACC → ethylene. ACC deaminase converts ACC into α-ketobutyrate and ammonia. Lower ACC reduces substrate availability for ethylene-forming enzyme (ACC oxidase). Concept / Approach: By enzymatically removing ACC, the flux to ethylene decreases, delaying ripening and mitigating stress responses where ethylene surges are detrimental. Step-by-Step Solution: Identify ACC as the immediate ethylene precursor.Recall ACC deaminase reaction: ACC → α-ketobutyrate + NH3.Conclude functional outcome: reduced ethylene biosynthesis. Verification / Alternative check: Transgenic and endophytic ACC deaminase systems consistently show reduced ethylene levels and improved stress tolerance or delayed ripening. Why Other Options Are Wrong: Direct ethylene synthesis: ethylene is produced by ACC oxidase, not ACC deaminase.Polygalacturonase synthesis: unrelated cell-wall enzyme.Blocking SAM formation or reversing ethylene: not the enzyme’s reaction. Common Pitfalls: Mixing up ACC oxidase (ethylene forming) with ACC deaminase (ethylene-reducing via ACC degradation). Final Answer: Degradation of ACC, the immediate precursor to ethylene.

Transgenic Plant Questions