19. Genetic Technology

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 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.

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.

Different enzymes perform different jobs in preparing and joining a desired gene: restriction endonucleases cut DNA at specific sequences, reverse transcriptase makes cDNA from mRNA, DNA polymerase completes the cDNA into double-stranded DNA, and DNA ligase joins DNA backbones.

Restriction endonuclease — cuts the DNA or DNA construct at a recognised base sequence. An uneven cut can leave sticky ends, whose exposed bases can hydrogen-bond with complementary ends made by the same enzyme.
Reverse transcriptase — uses the mRNA for the desired gene as a template to make single-stranded cDNA; because processed mRNA lacks introns, the cDNA also lacks those introns.
DNA polymerase — adds complementary nucleotides to the single-stranded cDNA to make a double-stranded gene sequence.
DNA ligase — forms phosphodiester bonds in the sugar–phosphate backbone so the isolated gene can be joined into the DNA construct.

A typical enzyme order is:

1. Obtain or isolate the desired sequence.
2. Use compatible restriction cuts when a DNA construct is being prepared.
3. Use reverse transcriptase and then DNA polymerase if the source is mRNA.
4. Use DNA ligase to seal the joined DNA.
   The exact branch depends on the gene source.

Restriction endonucleases cut the surrounding DNA or DNA construct, not “the gene” as an enzyme role; the same restriction enzyme is used to make compatible ends. These enzymes are not interchangeable: cutting, copying and joining are separate jobs. The matched SME page does not require vector, promoter, marker, PCR or gel mechanisms here; those are separate cards.

A promoter is a non-coding DNA region that controls expression of a nearby transferred gene. It contains the transcription start point where the host RNA polymerase binds and recognises the template strand, so the gene can be transcribed.

Transferred gene without a suitable promoter → host RNA polymerase cannot start the required transcription reliably → little or no gene expression. Therefore a genetic construct must pair the coding sequence with a promoter that the host cell can recognise and regulate. Promoter choice is host- and condition-dependent: bacteria do not switch all genes on at once, and expression depends on the growing conditions and regulatory context.

Promoter — starts and regulates transcription of the desired gene; it is not translated into the product.
Selectable marker — travels with the desired gene and allows cells that received recombinant DNA to be selected or identified.
Reporter marker — produces a detectable readout, such as fluorescence, so expression or successful alteration can be located; the readout is evidence about the marker, not automatic proof that the desired product functions correctly.

1. Place the desired gene with a promoter that the host RNA polymerase can recognise.
2. Include a marker when transformed cells must be selected or identified.
3. Introduce the construct into host cells.
4. Use the marker readout to find likely altered cells, then interpret desired-gene expression separately from marker detection.

A promoter controls transcription; a marker identifies or selects cells. They are different DNA elements with different jobs, even when both are included in the same construct. This card does not expand into PCR, gel electrophoresis, microarrays or bioinformatics, and it does not treat a marker signal as proof of complete product function.

A marker gene is transferred with a desired gene so that cells containing recombinant DNA can be selected or identified. The marker provides evidence about which cells received the construct; it is not the same DNA element as the promoter that starts transcription.

Selectable marker — gives transformed cells a survival or growth difference under the selection condition, allowing likely recombinant cells to be selected. Antibiotic-resistance markers can do this, but their possible spread to pathogenic bacteria may reduce antibiotic effectiveness.
Reporter marker — produces a visible or measurable signal, such as GFP fluorescence under ultraviolet light, allowing altered cells or marker expression to be located. Fluorescent markers avoid selecting with antibiotic-containing growth media and avoid the specific resistance-transfer concern.

1. Transfer the desired gene together with the marker construct.
2. Allow the host cells to grow under the relevant selection condition or use the reporter readout.
3. Retain or identify cells that show the marker phenotype or signal.
4. Interpret the result cautiously: marker detection supports successful construct transfer and/or marker expression, but does not by itself prove that the desired gene product is correctly folded, functional or at the expected level.

Promoter present and recognised → transcription of the linked gene can begin. Marker present and read out → cells carrying or expressing the construct can be found. Thus promoter and marker work at different checkpoints in the same construct: one supports expression, the other supports selection or identification.

A marker signal is not automatic proof of complete desired-product expression or function. Marker choice also has consequences: antibiotic-resistance markers can spread by genetic transfer, whereas fluorescent reporter markers can be detected directly with ultraviolet light. PCR, gel electrophoresis, microarrays and bioinformatics remain separate cards.

Gene editing changes DNA at a chosen site in the genome by inserting, deleting or replacing a sequence. It is a form of genetic engineering, but the aim is a targeted change to the existing genome rather than random insertion of foreign DNA.

1. Identify the target sequence and the faulty DNA change that must be corrected.
2. Direct a nuclease to the target: in the SME-supported CRISPR example, guide RNA determines the specific point and is attached to the Cas9 cutting enzyme.
3. Cut the DNA strands at that selected site.
4. Use the resulting DNA break to insert, delete or replace the faulty sequence with the intended DNA; the exact repair detail is not expanded beyond this course boundary.
5. Check the edited sequence and then ask whether the relevant gene is expressed and produces the intended function.

Targeted gene editing — guide-directed cutting at a selected genome site, followed by insertion, deletion or replacement.
Earlier vector insertion — DNA delivery could insert into other genes, so the location and consequences were less predictable.
Shared boundary — greater targeting improves the location of the intended change, but it does not automatically prove that every cell was edited, that expression is correct, or that the resulting function is safe.

Target recognition → site-specific cut → sequence change → sequence and expression/function checks. The target sequence defines where the edit is made; the edit type determines whether DNA is inserted, deleted or replaced. No foreign DNA is required to remain in the edited genome.

“Targeted” does not mean automatically perfect or automatically functional. This card stays at the SME-supported guide RNA/nuclease and insertion–deletion–replacement level: it does not add other CRISPR proteins, clinical examples, ethical claims, PCR, gel electrophoresis, microarrays or bioinformatics.

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 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.

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.

Bioinformatics organises, stores and analyses biological data such as genome sequences, expressed-gene data and protein amino-acid sequences. Database comparisons can reveal sequence similarity and help infer possible relatedness or model-organism relevance, but the result remains evidence rather than automatic proof of function.

1. Define the question and check the input data: identify whether the query is a DNA sequence, expressed-gene dataset or protein sequence, and check that the sequence and annotation are sufficiently complete for the intended comparison.
2. Search an appropriate reference database containing comparable sequence, expression or protein information. The database scope and quality determine what can be found and how relevant the matches are.
3. Align or compare the query with reference entries using a suitable sequence-comparison algorithm. Record similarity and conserved regions rather than treating one short match as a complete interpretation.
4. Apply the stated comparison settings and any supplied threshold or significance rule consistently; do not invent a universal cut-off. A result is conditional on the reference set, algorithm and data quality.
5. Infer cautiously: conserved or highly similar sequence regions can support a possible common function or evolutionary relationship, but sequence homology does not by itself prove identical function, expression, phenotype or safety.
6. Use independent biological or experimental evidence to test the proposed function or relationship before making a stronger claim.

Reference database — determines which known sequences or proteins can be compared.
Similarity/alignment — identifies matching or conserved regions and supports a hypothesis about relatedness or function.
Data quality and settings — incomplete, noisy or poorly matched inputs, together with algorithm or threshold choices, can change the apparent result.
Inference boundary — a database match is a starting point for interpretation, not a direct measurement of gene function or a replacement for validation.

Do not treat bioinformatics as the PCR, gel-electrophoresis or microarray laboratory workflow. No database name, software setting, numerical threshold or degree of similarity is assumed here; state only what the supplied data and reference comparison support.

Recombinant DNA allows microbes or cultured cells to produce human proteins such as insulin, factor VIII or adenosine deaminase.

The therapeutic product must be made in a form that is safe, correctly folded and controllable in dose.

Recombinant insulin avoids relying on extracting the same hormone from animal pancreases.

Producing a human protein does not remove immune, dose or manufacturing risks.

Screening can identify variants associated with conditions such as BRCA1/BRCA2 cancers, Huntington’s disease or cystic fibrosis.

Interpret a result as risk or carrier information, not as a guaranteed future outcome, and consider confirmatory testing.

A BRCA variant may increase breast-cancer risk while not determining whether cancer will develop.

A screening test can have false positives, false negatives and consequences for relatives; genotype is not destiny.

Gene therapy aims to add, replace or edit genetic material so affected cells gain a useful function.

Delivery, duration of expression, immune response and the target tissue determine whether treatment helps.

A vector delivering a functional sequence to retinal cells may improve an inherited eye disorder if enough cells are reached.

Gene therapy is not a universal cure: the delivery route and cell type limit the result.

Screening and gene therapy raise questions about consent, privacy, discrimination, access, reproductive decisions and long-term risk.

A defensible judgement separates evidence about safety or benefit from values about who should decide and who receives access.

Offering a predictive test may help planning but also create anxiety or insurance concerns if privacy is weak.

Ethical disagreement is not solved by listing “pros and cons”; specify stakeholders, evidence, uncertainty and decision criteria.

Genetic engineering can improve yield, quality or resilience, but the benefit depends on the trait, environment and farming system.

Assess productivity alongside inputs, ecological effects, farmer access and food safety.

A crop engineered for pest resistance may reduce losses, but its benefit changes if pests evolve resistance or farmers cannot access the seed.

“GM” describes a method, not a guarantee of sustainability or nutritional benefit.

GM salmon can be modified for growth, soybeans can be herbicide-resistant and cotton can express insect resistance.

Explain the introduced trait and its management consequence rather than treating all GM crops as equivalent.

Insect-resistant cotton can reduce damage from a target pest while requiring resistance-management strategies.

A trait can create trade-offs: herbicide resistance may alter herbicide use, and pest resistance can evolve.

GM food production has potential benefits and risks involving ecology, health, ownership, livelihoods and consumer choice.

Evaluate a proposal by asking what evidence supports the specific trait, who bears risks and how monitoring or regulation works.

A drought-tolerant crop may help farmers in dry regions but raise concerns about seed access and gene flow.

A general claim about GMOs cannot settle a specific case; conclusions must name the organism, trait and context.