301. A cotton plant contains and expresses an appropriate cry gene originally obtained from Bacillus thuringiensis. No living B. thuringiensis cells are present in the plant. Which conclusion is most accurate?
ⓐ. The plant cannot show Bt-mediated resistance because live bacterial cells must colonise every leaf for resistance
ⓑ. The cry gene and Bacillus thuringiensis are interchangeable terms
ⓒ. The plant can resist only if bacterial spores continually reproduce inside its tissues
ⓓ. The introduced cry gene can provide Bt protein without living B. thuringiensis in the crop
Correct Answer: The introduced cry gene can provide Bt protein without living B. thuringiensis in the crop
Explanation: Bt crop technology uses genetic information derived from Bacillus thuringiensis rather than requiring the crop to contain living populations of the bacterium. An appropriate cry gene encoding a Bt insecticidal protein can be introduced into a crop so that plant tissues produce the relevant protein. When a susceptible target insect feeds on the crop, the Bt protein can exert its insecticidal effect through the characteristic gut-associated mechanism. The bacterium, the cry gene and the Cry or Bt protein are related but distinct biological entities. The bacterium is the original biological source, the cry gene carries the coding information, and the expressed protein is the insecticidal product responsible for crop protection.
302. A Cry protein gives strong protection against Pest P, but a second pest belonging to a different susceptible insect group begins damaging the same crop. What is the most appropriate next biological consideration?
ⓐ. Reassess the pest and choose a cry gene with suitable toxin specificity
ⓑ. Assume that every Cry protein must kill all insect pests equally
ⓒ. Replace the cry gene with a C-peptide sequence
ⓓ. Use the same toxin because pest identity is irrelevant to Bt specificity
Correct Answer: Reassess the pest and choose a cry gene with suitable toxin specificity
Explanation: Bt toxins are not universal insect poisons. Their effectiveness depends on the identity and susceptibility of the target pest, which is why different cry genes are associated with different insect targets. A Cry protein that performs well against one pest cannot automatically be assumed to provide equivalent protection against another. Selection of a suitable gene requires linking the crop problem with the biology of the target insect. This principle explains why cryIAc and cryIIAb are associated with cotton bollworms, while cryIAb is associated with corn borer examples. Pest identity is an important biological variable in designing Bt-based crop protection rather than an incidental detail. Expression of a cry gene in a crop supplies the insecticidal protein, while later activation and action occur in the susceptible insect.
303. Tobacco plants in one field develop severe root infestation by Meloidogyne incognita and subsequently show a substantial decline in productivity. Which interpretation best connects the observations?
ⓐ. Meloidogyne incognita is a leaf-feeding insect whose damage is restricted to cotton bolls
ⓑ. The organism primarily improves mineral-use efficiency in tobacco roots
ⓒ. Meloidogyne incognita is a parasitic nematode that attacks tobacco roots and can reduce yield substantially
ⓓ. The yield decline demonstrates failure of insulin production in the plant
Correct Answer: Meloidogyne incognita is a parasitic nematode that attacks tobacco roots and can reduce yield substantially
Explanation: Meloidogyne incognita is the parasitic nematode used in the RNA interference example. It infects tobacco roots and can cause substantial reduction in crop yield. This host-location-effect relationship is important as it establishes the agricultural problem that RNAi-based engineering is designed to address. The organism is not a boll-feeding insect and should not be treated as a Bt target simply as both examples concern pest resistance. In the RNAi strategy, tobacco is engineered to generate RNA capable of silencing an essential nematode mRNA, interfering with parasite survival in the host roots. Correct identification of the nematode, its infection site and its impact on yield provides the biological context for the later molecular mechanism.
304. An RNA-genome virus infects a eukaryotic cell and generates viral RNA, but none of that RNA is complementary to a particular host mRNA under study. What follows for RNA interference against that host mRNA?
ⓐ. Bt-type pore formation will selectively silence the host mRNA
ⓑ. Any viral RNA automatically destroys every cellular mRNA
ⓒ. The host mRNA must be silenced because viral infection alone is sufficient in that infected cell
ⓓ. Sequence-specific silencing of that host mRNA is not expected merely from non-complementary viral RNA
Correct Answer: Sequence-specific silencing of that host mRNA is not expected merely from non-complementary viral RNA
Explanation: RNA interference is sequence-specific. Viral infection with an RNA genome can provide RNA that participates in a cellular silencing response, but effective targeting of a particular mRNA depends on complementary sequence relationships that permit the silencing machinery to recognise that target. In the stated condition, the viral RNA lacks complementarity to the host mRNA being considered, so infection alone does not justify predicting silencing of that host transcript. This qualifier is important when applying the natural-defence concept: the presence of RNA or double-stranded RNA is not a universal signal for destruction of every cellular message. Bt-mediated pore formation belongs to an unrelated protein-toxin mechanism. RNAi protects through selective nucleic-acid recognition and suppression of corresponding gene expression.
305. A transgenic tobacco plant produces both sense and antisense transcripts of a nematode gene, but a sequence alteration prevents the two transcripts from being sufficiently complementary to form the intended double-stranded RNA. What is the most likely consequence?
ⓐ. Bt protoxin activation in the nematode will increase
ⓑ. RNAi-mediated silencing of the target nematode mRNA will be weakened
ⓒ. The plant will automatically begin producing human insulin
ⓓ. The nematode mRNA will be silenced more strongly because complementarity is unnecessary
Correct Answer: RNAi-mediated silencing of the target nematode mRNA will be weakened
Explanation: The engineered RNAi strategy depends on complementary sense and antisense RNA associating to form double-stranded RNA. That double-stranded RNA is central to sequence-specific silencing of the corresponding nematode mRNA. If the two transcripts can no longer pair effectively, formation of the intended double-stranded RNA is reduced, weakening the silencing mechanism. The change interrupts an earlier molecular step than a mutation in the nematode target itself, but the downstream consequence is similar: less effective suppression of the required parasite gene. Complementarity is not an optional feature of RNA interference. It is precisely what gives the mechanism its sequence specificity and allows the transgenic host to interfere selectively with nematode gene expression. The engineered tobacco example links vector-mediated gene transfer with a natural eukaryotic gene-silencing defence mechanism. Sequence specificity is the central boundary that prevents RNAi from being interpreted as a non-selective destruction of all cellular RNA.
306. A recombinant microorganism produces a therapeutic human protein in very large quantity, but the product remains mixed with unwanted cellular material and has not been suitably purified. Which conclusion is most appropriate?
ⓐ. High expression still requires downstream recovery and purification before the therapeutic is usable
ⓑ. High expression automatically converts the crude mixture into a finished medicine
ⓒ. Purification is unnecessary whenever recombinant DNA technology is used
ⓓ. The therapeutic must be classified as an agricultural GMO rather than a medical product
Correct Answer: High expression still requires downstream recovery and purification before the therapeutic is usable
Explanation: Biotechnology production involves more than generating a large amount of the desired molecule. After biological production, the useful product must be recovered and purified from the surrounding cellular material and other substances present in the production system. This downstream stage is distinct from selecting an appropriate biological catalyst or creating favourable conditions for production. In a medical application, purity and product recovery are especially important because the intended therapeutic molecule must be separated from unwanted components before it can serve its purpose. The scenario connects recombinant therapeutic production with a broader biotechnology principle: high-yield expression solves the production problem but does not by itself complete the pathway from biological synthesis to usable product.
307. In the Eli Lilly strategy, human insulin A and B chains were produced separately in E. coli and later combined. Which feature of mature insulin makes this approach biologically sensible?
ⓐ. Mature insulin normally consists entirely of C peptide
ⓑ. Mature insulin contains a single uninterrupted chain that must retain proinsulin
ⓒ. Mature insulin has A and B chains but lacks C peptide
ⓓ. Mature insulin is normally a bacterial crystal protein
Correct Answer: Mature insulin has A and B chains but lacks C peptide
Explanation: Mature human insulin contains two polypeptide chains, A and B, connected through appropriate disulphide bridges. C peptide occurs in the precursor proinsulin but is removed during normal maturation and is absent from the final hormone. Producing the mature A and B chains separately in bacterial systems directly provides the two polypeptide components needed for the mature product. After extraction, the chains can be combined and the required structural linkages established. The strategy does not require C peptide to remain as part of the final molecule. Understanding the mature structure explains why separate recombinant production of A and B chains can be followed by final assembly into functional human insulin. The therapeutic molecule must retain the defining human insulin structure regardless of the particular recombinant route used to manufacture it.
308. Natural proinsulin requires removal of C peptide during maturation. In a recombinant strategy, however, the mature A and B chains are produced separately rather than as one intact proinsulin precursor. Which processing requirement is consequently avoided at the expression stage?
ⓐ. Formation of the A-chain sequence
ⓑ. Cleavage of C peptide from an expressed proinsulin precursor
ⓒ. Production of the B-chain sequence
ⓓ. Final establishment of the correct relationship between A and B chains
Correct Answer: Cleavage of C peptide from an expressed proinsulin precursor
Explanation: In natural insulin biosynthesis, proinsulin contains the A and B regions together with C peptide, and maturation includes removal of the C-peptide segment. The recombinant strategy described for separate-chain production does not begin by expressing one complete proinsulin molecule in the bacterial system. Instead, DNA sequences for the mature A and B chains are expressed independently. Because those products do not include the connecting C peptide, a C-peptide cleavage step is not required for those separately expressed chains. Final assembly is still essential, since the recovered A and B chains must be combined correctly and linked through appropriate disulphide bonds. Thus, separate-chain expression changes the production route without changing the structural requirements of mature insulin.
309. Cultured lymphocytes from an ADA-deficient patient are successfully exposed to a retroviral vector, but the vector carries a defective ADA cDNA that cannot produce functional enzyme. What is the most likely outcome after reinfusion?
ⓐ. The lymphocytes will permanently cure ADA deficiency because vector entry alone is sufficient
ⓑ. The defective cDNA will automatically repair itself after reinfusion
ⓒ. Enzyme-replacement therapy will occur spontaneously
ⓓ. ADA function is unlikely to return because the therapeutic cDNA is non-functional
Correct Answer: ADA function is unlikely to return because the therapeutic cDNA is non-functional
Explanation: Successful gene therapy requires more than delivery of any DNA into patient cells. The introduced genetic material must contain functional information capable of restoring the missing biological activity. In the ADA example, the retroviral vector serves as the delivery vehicle, while functional ADA cDNA is the therapeutic cargo. If the vector enters the lymphocytes but carries a defective cDNA, the cells do not acquire the intended capacity to produce functional ADA enzyme. Reinfusion of such cells would not accomplish the corrective goal. This changed condition separates vector delivery from gene function and shows why both components of the treatment must work: a suitable vector must reach the target cells, and the gene it delivers must itself be functional.
310. Functional ADA cDNA is introduced successfully into cultured lymphocytes from an ADA-deficient patient. The corrected cells are expanded in culture but are never returned to the patient. Which step is missing from the therapeutic sequence?
ⓐ. Production of Bt toxin inside the cultured cells
ⓑ. Removal of C peptide from the ADA enzyme
ⓒ. Reinfusion of the genetically corrected lymphocytes into the patient
ⓓ. Conversion of the lymphocytes into bone marrow before treatment
Correct Answer: Reinfusion of the genetically corrected lymphocytes into the patient
Explanation: Ex vivo ADA gene therapy involves a sequence in which the patient's lymphocytes are removed and cultured, functional ADA cDNA is introduced using an appropriate vector, and the genetically corrected cells are then returned to the patient. Genetic correction in a culture vessel does not provide therapeutic benefit to the patient unless those cells are reinfused. The scenario has already completed isolation, culture and genetic modification, so reinfusion is the missing step. This distinction illustrates why ex vivo therapy is a complete cell-handling pathway rather than merely a laboratory gene-transfer experiment. The genetically corrected cells must ultimately re-enter the patient if their restored ADA-producing capability is to contribute to treatment. ADA treatment strategies differ in whether they supply enzyme protein, replacement cells or functional genetic information to patient cells. Durability depends on the persistence and developmental contribution of corrected cells, not only on successful delivery of functional ADA cDNA.
311. A qualitative disease-progression graph shows pathogen nucleic acid becoming detectable by a sensitive molecular method at Stage P. Obvious clinical symptoms appear later at Stage Q. No numerical thresholds are provided. Which interpretation best explains the interval between P and Q?
ⓐ. Sensitive nucleic-acid amplification can reveal a low pathogen burden before obvious symptoms
ⓑ. Obvious symptoms necessarily appear before any pathogen nucleic acid becomes detectable
ⓒ. Pathogen nucleic acid becomes detectable only after symptoms reach maximum severity
ⓓ. Molecular diagnosis depends on pathogen disappearance before symptoms develop
Correct Answer: Sensitive nucleic-acid amplification can reveal a low pathogen burden before obvious symptoms
Explanation: Early in an infection, pathogen nucleic acid may already be present even though the amount of pathogen and associated tissue disturbance are still insufficient to produce clear clinical symptoms. PCR can amplify a selected nucleic-acid target from a very small starting quantity, making the infection detectable during this earlier period. Stage P represents molecular detectability, while Stage Q represents the later onset of obvious symptoms. The graph does not require an invented numerical threshold to illustrate the biological relationship. Its educational value lies in showing why amplification-based molecular diagnosis can identify an infection before symptom-dependent conventional diagnosis becomes informative. Molecular diagnosis can reveal biological evidence before obvious symptoms when the relevant target is detectable at low abundance. ELISA uses specific antigen-antibody recognition and can be designed to detect either pathogen antigen or host antibody.
312. A patient's gene contains a mutation, but the mutation lies far outside the short sequence recognised by a particular labelled probe. The probe-binding region itself remains fully complementary to the probe. What result is most likely under otherwise suitable conditions?
ⓐ. Hybridisation must fail because any mutation anywhere in the gene prevents probe binding
ⓑ. The probe will become an antibody against the mutant gene
ⓒ. PCR amplification will necessarily stop even though no PCR condition is described
ⓓ. The probe can still hybridise because its own complementary target sequence remains unchanged
Correct Answer: The probe can still hybridise because its own complementary target sequence remains unchanged
Explanation: Nucleic-acid probe hybridisation depends on complementarity between the probe and the particular target sequence to which it is designed to bind. A mutation elsewhere in the gene does not automatically disrupt that local complementary relationship. If the actual probe-binding region remains unchanged, the probe can still pair with its target under suitable conditions and produce the expected labelled signal. This changed-condition problem highlights the sequence specificity of probe-based diagnosis. A probe does not assess every nucleotide in an entire gene simultaneously; it reports on the sequence relationship at its own target region. Only changes that sufficiently disrupt the relevant complementary sequence are expected to interfere directly with that probe's hybridisation. PCR increases the amount of a selected nucleic-acid target, whereas probe methods and ELISA rely on different recognition principles. Early detection is valuable because visible symptoms may appear only after the pathogen or disease process has progressed further.
313. A DNA sample contains the exact sequence complementary to a nucleic-acid probe. Hybridisation occurs normally, but the probe was accidentally prepared without its radioactive label. In the autoradiographic probe assay, what is the most likely observation?
ⓐ. An unlabelled probe cannot base-pair with a complementary target sequence
ⓑ. Hybridisation can occur, but autoradiographic detection fails without the radioactive label
ⓒ. An unlabelled probe produces a stronger film signal after binding its target
ⓓ. Loss of the label converts nucleic-acid hybridisation into an antigen-antibody assay
Correct Answer: Hybridisation can occur, but autoradiographic detection fails without the radioactive label
Explanation: Probe binding and probe detection are related but distinct parts of the assay. Complementary base pairing allows the single-stranded probe to hybridise with its matching nucleic-acid sequence. The radioactive tag does not create complementarity; it provides a detectable marker that can reveal where hybridisation has occurred through autoradiography. If the probe lacks that label, it may still bind its target normally, but the expected autoradiographic signal cannot be produced from the unlabelled probe. The experiment distinguishes molecular recognition from signal detection. This reasoning also shows why a no-signal result can have more than one possible technical cause unless the experimental system and labelling controls are known to have worked properly. A labelled probe depends on complementary base pairing, so sequence alteration can change the expected hybridisation signal. Diagnostic evidence must be interpreted according to what the assay actually detects rather than treating all molecular tests as interchangeable.
314. An ELISA is specifically designed to detect a pathogen antigen in a patient's sample, and the test gives a positive result. What does the result most directly indicate?
ⓐ. The patient's DNA necessarily contains a cancer-associated mutation
ⓑ. A labelled nucleic-acid probe has hybridised with the pathogen genome
ⓒ. The pathogen-associated antigen recognised by the assay is present in the tested sample
ⓓ. The patient must already possess every possible antibody against the pathogen
Correct Answer: The pathogen-associated antigen recognised by the assay is present in the tested sample
Explanation: ELISA is based on specific antigen-antibody interactions, but the molecule being detected depends on how the assay is designed. In this case, the test is explicitly configured to detect a pathogen antigen, so a positive result directly supports the presence of that recognised antigen in the sample. Another ELISA design could instead detect antibodies made by the host against a pathogen, but that is a different diagnostic target. PCR and labelled nucleic-acid probes operate through nucleic-acid amplification and sequence complementarity rather than antigen-antibody recognition. Correct interpretation requires identifying not only the method but also the specific biological analyte the assay is designed to detect. ELISA uses specific antigen-antibody recognition and can be designed to detect either pathogen antigen or host antibody.
315. The historical reference states that mice constitute more than \(95\%\) of existing transgenic animals in the stated context. Which inference is scientifically appropriate?
ⓐ. Mice are the predominant transgenic-animal model in that context, but other transgenic species also exist
ⓑ. Every transgenic animal must be a mouse
ⓒ. Rats, rabbits, pigs, sheep, cows and fish cannot be made transgenic
ⓓ. The figure proves that mice account for exactly \(100\%\) of all present-day transgenic animals in the cited context
Correct Answer: Mice are the predominant transgenic-animal model in that context, but other transgenic species also exist
Explanation: A value greater than \(95\%\) indicates strong predominance, not exclusivity. Rats, rabbits, pigs, sheep, cows and fish are also examples of transgenic animals. The correct interpretation is that mice represent the great majority in the historical statement while other species remain part of transgenic-animal research. The numerical figure should also be understood in its historical reference rather than converted into a permanent present-day census. The interpretation requires reading quantitative biological information rather than simple recall: a dominant category can account for most examples without being the only category that exists.
316. Cystic fibrosis appears in two different transgenic-animal contexts. In Project P, an animal is engineered to reproduce important features of cystic fibrosis for studying disease mechanisms. In Project Q, an animal is engineered in an attempt to produce a useful biological product related to treatment. How should the projects be classified?
ⓐ. Both are automatically chemical-safety tests because the disease name is the same
ⓑ. P is a disease-model application, whereas Q is a biological-product application
ⓒ. P is biological-product production, whereas Q is only normal-development research
ⓓ. Both must have identical purposes whenever the same disease is mentioned
Correct Answer: P is a disease-model application, whereas Q is a biological-product application
Explanation: Classification of a transgenic-animal project depends on what the animal is being used to accomplish, not merely on the disease name appearing in the description. Project P reproduces features of a human disorder so researchers can investigate disease mechanisms or possible treatments; this is disease modelling. Project Q instead uses the animal as a system for producing a potentially useful biological product associated with therapy, so it belongs to biological-product production. Cystic fibrosis can appear in more than one educational context without creating a contradiction. The experimental objective, rather than the label of the disease, determines which transgenic-animal purpose is being illustrated. Transgenic animals serve several distinct purposes, so the project should be classified from its measured phenotype, produced protein or safety endpoint. Rosie's example illustrates a transgenic animal used to alter the protein composition of a recoverable biological product.
317. A transgenic animal contains an introduced human gene intended for production of a therapeutic protein, but the gene is not expressed in any tissue. Which conclusion is most appropriate?
ⓐ. The animal must still produce large quantities of the therapeutic protein because possession of DNA is sufficient
ⓑ. Failure of expression automatically turns the animal into a disease model
ⓒ. The therapeutic protein will appear only because the animal is transgenic
ⓓ. The intended biological-product application fails because useful protein production requires expression of the introduced gene
Correct Answer: The intended biological-product application fails because useful protein production requires expression of the introduced gene
Explanation: Transgenic biological-product production depends on more than the physical presence of introduced DNA. The relevant gene must be expressed so that the encoded useful protein is actually synthesised. If the introduced human gene remains silent, the animal may still contain the foreign DNA, but it cannot serve the intended role as a production system for that therapeutic protein. This distinction mirrors the broader definition of a functional transgenic application, where possession and expression of an introduced gene are biologically important. The experiment separates gene presence from gene function. A biotechnology objective based on protein production succeeds only when the genetic modification leads to the required expressed product.
318. Rosie's milk is described as containing human alpha-lactalbumin at \(2.4\,\text{g L}^{-1}\). Sample P contains \(0.75\,\text{L}\) of the milk and Sample Q contains \(1.25\,\text{L}\). At the same concentration, what are the total mass of human alpha-lactalbumin in both samples together and the mass ratio P:Q?
ⓐ. \(4.8\,\text{g}\) and \(3:5\)
ⓑ. \(4.8\,\text{g}\) and \(5:3\)
ⓒ. \(3.0\,\text{g}\) and \(3:5\)
ⓓ. \(6.0\,\text{g}\) and \(3:5\)
Correct Answer: \(4.8\,\text{g}\) and \(3:5\)
Explanation: The same concentration applies to both samples, so each protein mass is concentration multiplied by its volume. For Sample P,
\[
2.4\,\text{g L}^{-1} \times 0.75\,\text{L} = 1.8\,\text{g},
\]
while Sample Q contains
\[
2.4\,\text{g L}^{-1} \times 1.25\,\text{L} = 3.0\,\text{g}.
\]
Together the samples contain \(1.8 + 3.0 = 4.8\,\text{g}\). Their mass ratio is \(1.8:3.0\), which simplifies to \(3:5\). The ratio can also be checked directly from the volumes: when concentration is identical, protein mass is directly proportional to volume, and \(0.75:1.25\) also reduces to \(3:5\). The calculation combines two quantitative decisions rather than a single substitution. Biologically, the calculation interprets the concentration of human alpha-lactalbumin produced in Rosie's milk and relates sample size to the recoverable mass of the transgenic human protein.
319. Compare the two vaccine-related biotechnology activities below.
| Activity | Primary purpose |
|---|
| P. Recombinant expression of a selected vaccine-related biological product | Production |
| Q. Use of an appropriate transgenic mouse before wider human use of a vaccine | Safety assessment |
Which interpretation is correct?
ⓐ. P and Q are both methods for producing the same vaccine inside a mouse
ⓑ. Q is recombinant production, whereas P is chemical-toxicity testing
ⓒ. P concerns production of vaccine-related material, whereas Q concerns pre-human vaccine-safety testing
ⓓ. The two activities are identical because both involve biotechnology
Correct Answer: P concerns production of vaccine-related material, whereas Q concerns pre-human vaccine-safety testing
Explanation: Biotechnology can contribute to vaccines at more than one stage, and those roles should not be confused. Recombinant biological systems can be used conceptually to produce selected vaccine-related material. Transgenic animals may instead be used as experimental models to assess vaccine safety before broader human use. Transgenic mice are associated with polio-vaccine safety testing and the possibility of reducing reliance on monkeys. The mouse in such an experiment is a testing model rather than necessarily the production system for the vaccine. Distinguishing production from safety assessment clarifies how similar biotechnology tools can participate in different parts of a medical application.
320. For rapid chemical-safety testing, researchers intend an introduced gene to make an animal unusually sensitive to a toxic substance. Genetic analysis confirms that the gene is present, but expression fails completely. What is the most likely consequence?
ⓐ. The animal must become even more sensitive because silent genes produce stronger phenotypes
ⓑ. The animal will automatically begin testing vaccine safety instead
ⓒ. Toxicity results will necessarily appear faster because gene presence alone is sufficient
ⓓ. The sensitivity advantage may be lost because the introduced gene is not expressed
Correct Answer: The sensitivity advantage may be lost because the introduced gene is not expressed
Explanation: Chemical-safety testing with a specially engineered transgenic animal depends on expression of the introduced genetic change that increases sensitivity to the toxic substance. If the gene is physically present but not expressed, the intended altered phenotype may not develop. Without that enhanced responsiveness, the animal may no longer provide the quicker or more sensitive toxicity assessment for which it was designed. This case again separates gene presence from functional gene expression. The experimental value of a transgenic model lies in the biological consequence produced by the introduced gene, not merely in confirming that foreign DNA can be detected in the genome. Disease modelling, biological-product production, vaccine-safety testing and chemical-safety testing are separate applications even though each can use a transgenic animal.
