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19. Genetic Technology

Syllabus
9700–2028–2029
Section
19
Level
A2

19.1 Principles of Genetic Technology

Syllabus
9700–2028–2029
Topic
19.1
Level
A2

Recombinant DNA

Recombinant DNA is DNA made by combining nucleotide sequences from two or more different sources. The universal genetic code makes it possible for a sequence from one organism to be read in another organism, although the code itself does not guarantee successful expression.

  1. Select DNA sequences from the sources that provide the required information.
  2. Combine the sequences into one DNA construct; the construct is recombinant DNA.
  3. If the construct is introduced into a host cell, it may be copied and/or expressed there when the host has the required cellular control.
  4. A host containing introduced genetic material is a genetically modified organism (GMO); if the introduced sequence came from another species, it is also described as transgenic.

Shared codon meanings allow genetic information to be transferred between species: a host can potentially use the transferred sequence to make the same type of polypeptide. Recombinant DNA is therefore the altered DNA construct, not the whole organism and not automatically a useful product.

Keep the levels separate: recombinant DNA describes the DNA molecule or construct; transgenic describes introduced DNA from another species; GMO describes an organism with introduced genetic material. This card establishes the concept and its expression/replication boundary only. Restriction enzymes, vectors, promoters, PCR, gel analysis, applications and risk evaluation are later learning jobs.

Genetic engineering and gene expression

Genetic engineering deliberately modifies an organism by transferring genetic material so that a chosen characteristic can be produced. The transferred sequence becomes recombinant DNA in the host, but useful expression depends on the host being able to use the construct.

  1. Identify the gene associated with the desired characteristic.
  2. Isolate or obtain that gene as a suitable DNA sequence.
  3. Cut the relevant DNA and the delivery construct, then insert and join the gene to form recombinant DNA.
  4. Introduce the recombinant DNA into a host cell using a delivery system.
  5. Select or identify cells that received the construct, then clone the successful cells when required.
  6. Check that the transferred gene is expressed and that the intended product or characteristic is obtained.

The workflow has linked dependencies: the desired sequence must be obtained, the construct must be joined and delivered, and the host must recognise the regulatory information and express the gene. Enzymes, vectors, markers and promoters each support a later part of this chain; they are tools within the workflow, not interchangeable names for genetic engineering.

Do not treat transfer of DNA as proof of expression or a useful product. This card gives the whole engineering arc only. Restriction endonucleases, reverse transcriptase, DNA polymerase, ligase, vectors, promoters, markers, PCR, gel analysis, microarrays and bioinformatics are separate learning jobs; their detailed mechanisms belong to the matching cards.

Sources of genes

The desired gene can be obtained from donor genomic DNA, from donor mRNA as complementary DNA (cDNA), or by artificial synthesis. The best source depends on the sequence needed and whether non-coding introns must be excluded.

Use the source-selection method:

  1. Define the required characteristic and the nucleotide sequence that encodes it.
  2. Choose a source: extract the sequence from donor DNA; use specialised-cell mRNA as a template for cDNA; or design and synthesise the sequence from the genetic code.
  3. Obtain the desired sequence: the donor-DNA route cuts it from the genome, the mRNA route makes single-stranded cDNA and then double-stranded DNA, and the synthesis route joins short DNA pieces into a longer sequence.
  4. Check that the product contains the required gene sequence before handing it to the later DNA-transfer step.

Genomic DNA — directly represents a donor chromosome, but may include introns and other non-coding DNA.
cDNA from mRNA — reflects a gene that was expressed in the donor cell and lacks introns present in the processed mRNA.
Artificial synthesis — uses known genetic information to design the sequence, without cutting it from an existing genome; it can avoid introns or unnecessary non-coding sections.

These are alternative ways to obtain the desired gene, not three different gene functions. The matched SME page does not provide a separate DNA-library workflow, sequence-orientation assay, PCR protocol, gel method, or promoter/vector/marker mechanism; those details remain in their later cards and are not invented here.

Five tools perform distinct gene-transfer jobs

Gene transfer requires tools for obtaining, cutting, copying, joining and carrying DNA. Enzymes perform chemical reactions; a plasmid is a small circular DNA vector that carries the desired gene into a host cell and can replicate there.

Tool Role
Restriction endonuclease recognises a specific DNA sequence and cuts donor DNA and plasmid; using the same enzyme can create complementary sticky ends
Reverse transcriptase uses processed donor mRNA as a template to make single-stranded cDNA without introns
DNA polymerase adds complementary nucleotides to make the cDNA double stranded
DNA ligase forms phosphodiester bonds in the sugar-phosphate backbone, sealing the gene into the plasmid
Plasmid acts as a vector: accepts the gene, enters a host such as a bacterium, and is copied as the host/plasmid replicates

For an mRNA-derived gene: reverse transcriptase makes cDNA → DNA polymerase makes the second strand. Cut the gene and plasmid with the same restriction endonuclease → complementary ends pair → DNA ligase seals the recombinant plasmid → transfer it into host cells.

Sticky-end base pairing uses hydrogen bonds, but ligase seals the backbone with phosphodiester bonds. A plasmid carries and replicates DNA; it does not cut or join it.

A suitable promoter lets the host transcribe the gene

A promoter is a non-coding DNA sequence where transcription factors and RNA polymerase bind to start and control transcription of a nearby gene.

A desired gene taken from a donor may not include its promoter, or the donor promoter may not be recognised by the new host. Transferring a suitable promoter immediately upstream gives the host transcription machinery a binding and start region, so mRNA can be made and the gene can be expressed.

Promoter choice can control where, when and how strongly transcription occurs. A constitutive promoter can keep expression active, while a regulated promoter can respond to a condition or restrict expression to particular tissues when the construct and host support this.

The promoter is not translated and does not code for the desired protein. Transfer of a coding sequence without a host-recognised promoter may produce little or no transcription; the fluorescent marker used to check expression is taught separately.

Fluorescence reveals cells expressing the transferred construct

A fluorescent marker gene codes for a protein that fluoresces under suitable light. When it is transferred alongside the gene of interest, its visible product can reveal which cells are expressing the introduced construct.

  1. Add the marker gene to the same plasmid or construct as the gene of interest.
  2. Place both under the same promoter or linked expression control so they are transcribed together.
  3. Transfer the construct into host cells and allow transcription and translation.
  4. Expose the cells to the appropriate ultraviolet or blue light. Cells producing the fluorescent protein glow, identifying cells in which the linked transferred genes are being expressed.

Fluorescence requires marker-gene transcription, translation and correctly formed fluorescent protein. It therefore provides a rapid, non-destructive expression signal and allows fluorescent cells or tissues to be located.

Fluorescence directly confirms expression of the marker and supports expression of the linked gene under shared control. It does not by itself prove the amount, folding or biological function of the desired protein.

Gene editing changes DNA at a specific genome site

Gene editing is genetic engineering that inserts, deletes or replaces DNA at a specific site in an organism's genome. Targeting the site allows a chosen sequence or regulatory region to be modified rather than relying on uncontrolled insertion.

Edit DNA change Possible consequence
Insertion one or more nucleotides or a DNA sequence are added at the target can add information or alter reading/transcription control
Deletion selected DNA is removed can disrupt a sequence or remove a harmful section
Replacement target DNA is exchanged for a chosen sequence can correct a mutation or deliberately change codons/regulation

Specific target recognition → DNA alteration at that site → changed nucleotide sequence → possible change in transcription or amino-acid sequence and therefore phenotype. The edited sequence must be checked, followed by evidence that the intended expression or function changed.

Gene editing does not always add foreign DNA: deletion or replacement can modify an organism's existing genome. Specific targeting reduces uncertainty about location but does not by itself prove every cell was edited or that the result functions as intended.

PCR amplifies a DNA target

Polymerase chain reaction (PCR) is an in-vitro method for making many copies of a specific DNA target from a very small starting sample. Primers define which region is copied, while a thermostable DNA polymerase builds the new strands during repeated temperature cycles.

The reaction needs target DNA, forward and reverse primers, free nucleotides, a DNA polymerase, and a buffer. Primers are complementary to the ends of the target region, so they provide specificity and tell the polymerase where to begin. Taq polymerase is useful because it remains active after the high-temperature denaturation stage.

  1. Denaturation: heat the double-stranded template so hydrogen bonds break and the strands separate (about 95°C in the SME method).
  2. Annealing: lower the temperature so the forward and reverse primers bind to complementary sequences at the target ends (about 50–60°C).
  3. Extension: raise the temperature to the polymerase optimum so complementary strands are built from free nucleotides (about 72°C for Taq).
  4. Repeat the cycle: each cycle doubles the target DNA, producing exponential amplification of the region between the primers.

PCR amplifies the sequence between the primers, not every DNA molecule in the sample. Specificity therefore depends on primer binding and reaction conditions; a large signal is not automatically proof that the intended biological interpretation is correct. Contamination-control procedures are not specified on the matched SME page, so no extra protocol is invented here. Gel electrophoresis, microarrays and bioinformatics are separate cards.

Gel electrophoresis separates DNA fragments

Gel electrophoresis separates DNA fragments by their movement through a gel. DNA has a net negative charge because of its phosphate groups, so an electric field drives it towards the positive electrode; fragment size also affects how far it moves through the gel pores.

  1. Prepare the DNA sample and an agarose gel with wells, then submerge the gel in electrolyte solution.
  2. Load the DNA fragments into the wells and position the wells at the negative-electrode side.
  3. Apply the electric field: negatively charged DNA migrates through the gel towards the positive electrode.
  4. Separate the fragments: smaller or shorter fragments move more easily through the pores and therefore travel faster and farther than larger fragments.
  5. Make the separated DNA visible using an appropriate stain, fluorescent label or labelled-probe detection method supported by the investigation.
  6. Compare the band pattern with a size ladder and suitable control fragments to estimate sizes or assess similarity.
  7. Interpret cautiously: a matching pattern supports similarity under the tested preparation and conditions, but band evidence alone does not establish absolute identity.

Direction is set by DNA charge, while separation distance is influenced by fragment length and the gel conditions. A ladder or control provides the reference for comparison; distance is a conditional size estimate, and band brightness is not itself a fragment-length measurement.

The method gives evidence from a band pattern, not an automatic biological conclusion. No voltage, run time or fixed band count is assumed here. Microarrays and bioinformatics are separate cards.

Microarrays compare gene expression

A microarray is a chip carrying many gene-specific probes fixed in a grid of spots. Complementary labelled nucleic acids hybridise to the probes, allowing many genes to be detected at the same time; the signal can indicate sequence presence or, when mRNA-derived material is compared, relative gene expression.

  1. Choose probes with sequences complementary to the genes or transcripts being investigated and fix the probes at known spots on the chip.
  2. Collect the sample material. For a gene-expression comparison, collect mRNA and use reverse transcriptase to make corresponding cDNA; fluorescently label the sample nucleic acids.
  3. Denature the labelled material where needed so complementary single strands can pair with the probes.
  4. Allow the sample to hybridise with the probes on the chip, then wash away material that has not hybridised.
  5. Scan the chip using the supported fluorescence or ultraviolet detection method. A coloured spot indicates hybridisation to the corresponding probe.
  6. Compare spot colour or presence with the relevant sample, control and background. Presence can support sequence or transcript detection; for expression studies, relative spot intensity indicates relative mRNA abundance after appropriate comparison and normalisation.
  7. State the conclusion with its evidence boundary: a signal reports probe binding under the test conditions, not automatically a complete gene sequence, protein amount or biological function.

Sequence-presence reading — a coloured spot supports that a complementary sequence was detected.
Expression reading — stronger or weaker fluorescence is interpreted comparatively as more or less labelled cDNA from mRNA, provided samples were prepared and normalised comparably.
Controls and background — use matched controls and account for background signal before comparing spots; no probe number, intensity threshold or universal cut-off is assumed.

Microarrays are not a substitute for a full bioinformatics pipeline, and PCR and gel electrophoresis are separate cards. Spot intensity is a relative signal under the stated preparation and normalisation conditions, not an absolute expression value.

Shared databases make sequence and protein evidence usable

Biological databases store large, searchable collections of gene and genome nucleotide sequences, protein amino-acid sequences and protein structures. Computers can compare these records far faster and more consistently than manual analysis.

Database information Benefits
Gene and genome nucleotide sequences locate genes, design primers, identify mutations or disease alleles, compare individuals/species and analyse large genomes
Protein amino-acid sequences find conserved regions, compare related proteins and generate testable hypotheses about function or evolutionary relationships
Protein structures relate three-dimensional shape to function, compare binding/active sites and guide further experiments or treatment research

Central records let researchers worldwide search, align, process and share very large datasets, reuse reference sequences, update annotations and reproduce comparisons. This saves time, supports collaboration and allows new samples to be checked against known variants or structures.

A database result is evidence, not final proof. Its value depends on data quality, correct annotation and a suitable comparison; sequence similarity can suggest relatedness or function but still requires biological validation.

19.2 Genetic Technology Applied to Medicine

Syllabus
9700–2028–2029
Topic
19.2
Level
A2

Recombinant human proteins replace missing functions

Genetically modified microbes or cultured cells can make human proteins in large, controlled batches. The purified recombinant protein replaces or supplements a protein whose absence or deficiency causes disease.

Recombinant protein Treatment role Particular advantage
Insulin helps people with diabetes control blood glucose concentration human sequence is less likely than animal insulin to cause an immune/allergic response and avoids animal-source objections
Factor VIII restores part of the clotting pathway in haemophilia A avoids dependence on donated blood and greatly reduces transfer of blood-borne pathogens
Adenosine deaminase (ADA) supplies enzyme activity missing in some people with SCID, supporting lymphocyte/immune function provides a defined human enzyme when the patient's own functional ADA is insufficient

Shared advantages include a reliable large-scale supply, consistent composition, easier standardisation and purification, reduced dependence on animals or human donors, lower infection risk, and fewer religious or ethical objections to the source. Production can be adjusted to match demand.

Recombinant production reduces source-related problems but does not make treatment risk-free. Purity, correct folding, dose, route, immune reactions and manufacturing quality still require control; replacement protein may also need repeated administration.

Genetic screening turns inherited information into earlier choices

Genetic screening tests people or populations for alleles associated with inherited disease. Its advantage is earlier, more specific information that can guide monitoring, treatment, counselling and reproductive decisions before symptoms or an affected birth.

Example What a positive result indicates Advantages of knowing
BRCA1/BRCA2 variants increased risk of breast and some other cancers, not certainty of cancer more frequent surveillance, earlier detection/treatment, risk-reducing choices, testing of relatives and informed family planning
Huntington's disease allele a predictive result for a usually late-onset dominant disorder future care, work and financial planning; counselling; reproductive choices; a negative result may end uncertainty
Cystic fibrosis alleles two disease alleles can support diagnosis; one allele identifies a carrier carrier screening of couples, prenatal/newborn information, earlier treatment and respiratory/nutritional management, informed reproductive choices

A targeted programme can be cost-effective when it screens for well-characterised variants common in the population. Earlier identification can reduce complications or mortality when surveillance or treatment is available, and results can inform biologically related family members.

Interpret the result according to the condition: BRCA variants alter risk, Huntington's testing is predictive, and cystic-fibrosis testing may show affected or carrier status. Screening accuracy and variant interpretation still require confirmation and genetic counselling.

Gene therapy delivers a functional allele to affected cells

Gene therapy treats a genetic disease by delivering a functional allele, or making a corrective DNA change, in the somatic cells where the missing protein is needed. Expression of the functional gene restores some of the lost cell function.

  1. Identify the faulty gene and target tissue.
  2. Place a functional allele in a suitable vector, often a modified virus.
  3. Deliver the vector directly to the tissue or modify the patient's cells outside the body and return them.
  4. The target cells take up the gene and transcribe/translate it.
  5. Functional protein improves the affected pathway; monitor expression, benefit and adverse effects.
Disease example Target and route Intended result
ADA-deficiency SCID remove patient lymphocytes or blood-forming stem cells, introduce a functional ADA allele with a vector, then return modified cells ADA is produced, toxic metabolites are reduced and immune-cell function improves; short-lived lymphocytes may require repeat treatment, while modified stem cells may last longer
Inherited eye disease such as LCA2 inject a vector carrying a functional allele such as RPE65 into/near retinal target cells retinal cells express the functional protein and may preserve or improve vision; the eye is small, accessible and relatively isolated from systemic immune responses

Somatic gene therapy changes treated cells, not every cell and usually not the gametes, so the change is not inherited. Success depends on reaching enough suitable cells, expression lasting long enough, and avoiding immune reactions or harmful insertion/editing effects.

Genetic medicine balances benefit, autonomy, risk and access

A social and ethical discussion asks who benefits, who bears risk, who decides and whether access is fair. Genetic screening produces information affecting individuals and relatives; gene therapy actively changes cells and may involve uncertain long-term effects.

Consideration Potential benefit Concern or cost
Screening and timing early diagnosis can allow monitoring or treatment before irreversible symptoms false results or uncertain variants can cause unnecessary treatment, reassurance or anxiety
Consent and family informed people can plan care and reproduction; relatives may also learn relevant risk newborns or future children cannot fully consent; one person's result reveals information about relatives who may not want to know
Privacy and discrimination shared records can coordinate care and research insurers, employers or others could misuse genetic information if confidentiality is weak
Gene-therapy safety one treatment may restore function or prevent severe disability immune responses, harmful insertion/editing and unknown long-term effects may affect the patient
Cost and access effective screening can target scarce treatment early expensive programmes and therapies may widen inequality or divert resources from other care

A defensible decision states the context and weighs evidence. For example, newborn screening is stronger when disease is serious, the test is accurate and early treatment changes the outcome; its case weakens if follow-up treatment is unavailable or unaffordable. Counselling, voluntary informed consent where possible, data protection and long-term monitoring reduce—but do not remove—the concerns.

Somatic therapy affects the treated person; germline changes could pass to future generations who cannot consent and therefore raise an additional ethical boundary. Do not present 'ethical' as one fixed answer: identify stakeholders, benefit, evidence, uncertainty and a reasoned conclusion.

19.3 Genetically Modified Organisms in Agriculture

Syllabus
9700–2028–2029
Topic
19.3
Level
A2

GM traits can raise usable food output or quality

Genetic engineering can help meet food demand by giving farmed animals or crops a defined trait that increases productivity, reduces losses or improves the quality of the food produced.

Improvement route Trait effect Food-demand consequence
Faster or more efficient growth more biomass or marketable product is produced in a given time shorter production cycles or greater output
Resistance to pests, disease or competition fewer animals/plants or less tissue are lost before harvest a larger fraction of potential yield reaches consumers
Tolerance of a farm-management treatment the crop survives while weeds or another limiting factor are controlled reduced competition and higher crop yield
Improved product quality nutritional content, composition, storage life or processing quality is improved more useful or longer-lasting food from the harvest

The causal chain must be explicit: engineered gene → expressed protein/trait → changed growth, survival or product quality → changed usable yield. Benefits are greatest when the trait addresses a real local limitation and is combined with appropriate husbandry, crop management and access to food distribution.

Genetic engineering is a method, not a guarantee of more or better food. Yield can still be limited by water, minerals, climate, disease, management, cost and access; resistance may evolve and ecological effects may reduce long-term benefit.

Three GM examples use different routes to productivity

GM salmon, herbicide-resistant soybean and insect-resistant cotton increase productivity through different expressed traits: growth control, survival during weed control and protection from insect feeding.

GMO Engineered trait and mechanism Productivity benefit Management boundary
GM salmon growth-hormone expression is maintained for more of the year, so fish grow more rapidly reach market size sooner, increasing production rate prevent escape and assess welfare, competition and gene-flow risks
Herbicide-resistant soybean crop survives application of the relevant herbicide while susceptible weeds die less competition for light, water and mineral ions, so yield can rise and weed control may need less labour repeated use selects resistant weeds; gene flow and herbicide use/residues require management
Insect-resistant cotton a transferred bacterial gene produces a protein toxic to target insect larvae less feeding damage, higher usable yield and potentially less insecticide spraying target insects can evolve resistance; refuges/monitoring and non-target effects matter

Do not swap the mechanisms. The soybean is resistant to a herbicide; it does not make the herbicide. The cotton plant produces an insecticidal protein against target pests. The salmon modification changes the timing/level of growth-related expression rather than protecting a crop from weeds or insects.

Each trait can improve productivity only under suitable production conditions. Faster growth, easier weed control or reduced insect loss must be weighed against resistance evolution, containment, ecological effects and management cost.

GM food decisions depend on trait, evidence and stakeholders

Ethical and social evaluation of a GMO must name the organism, engineered trait, farming context and affected groups. A benefit to food supply may coexist with ecological, health, ownership, welfare or consumer-choice concerns.

Potential benefit Linked concern or condition Stakeholders
higher yield or less crop loss may increase supply and reduce food prices benefit depends on climate, soil, management and fair distribution farmers, consumers, governments
less insecticide spraying can reduce cost, worker exposure and environmental contamination pests may evolve resistance and non-target species must be monitored farm workers, neighbouring communities, ecosystems
herbicide-resistant crops simplify weed control and may reduce tillage herbicide use/residues, resistant weeds and gene flow to non-GM crops can create costs GM and non-GM farmers, consumers
rapid animal growth can increase production containment, animal welfare and effects of escaped organisms require evidence producers, consumers, animals, wild populations
patented seed can fund innovation and provide a useful trait price, seed saving, dependency and unequal access can disadvantage some farmers companies, farmers, regulators

Food safety testing, environmental risk assessment, post-release monitoring, resistance management and clear labelling can reduce uncertainty and protect consumer choice. Cultural or religious values may still lead people to different decisions even when they accept the same biological evidence.

Do not argue that all GMOs are safe, unsafe, ethical or unethical. Reach a conditional judgement: state the specific benefit, identify who bears each risk or cost, judge the quality of evidence, and explain which regulation or management would change the balance.