Classify sequence alterations — A substitution replaces a base, an addition inserts material and a deletion removes it. Duplication copies a segment, inversion reverses its orientation and translocation relocates material. State the scale and position of the change rather than assuming every rearrangement is one missing nucleotide in a translated exon.
Predict reading-frame effects — Within a translated coding region, insertion or deletion of a number of bases not divisible by three can alter downstream codon grouping. A three-base deletion can remove one residue without shifting all later codons. A rearrangement can also alter regulatory regions or interrupt a gene, so its effect cannot be predicted from length alone.
Connect mutation to function — A substitution may be synonymous, change an amino acid or introduce a stop signal. Altered sequence can affect folding, binding, stability or catalytic function, but some changes have little detectable effect. Trace the particular change through the supplied coding and functional information instead of claiming that any DNA change must cause a visibly abnormal organism.
Explain mutation sources — Replication errors can arise spontaneously, while mutagenic exposure can increase mutation probability. Mutation is not directed towards what would benefit the organism. The effects of an exposure depend on dose, repair, cell type and the affected sequence; a higher risk does not mean every exposed cell acquires the same change.
Stem cells, differentiation and potency
Explain selective expression during differentiation — Many specialised cells retain essentially the same nuclear genome but express different combinations of genes, producing different proteins and functions. Differentiation therefore does not ordinarily mean deleting all genes irrelevant to the cell's current role. Exceptions involving specialised loss of cellular material do not replace the general gene-regulation explanation.
Distinguish totipotent and pluripotent cells — In the mammalian developmental model, totipotent cells can contribute all cell types needed for an entire organism, including extraembryonic tissues, such as those contributing to the placenta, that support development outside the embryo itself. Pluripotent cells can generate the range of body-cell lineages but do not alone have the same whole-organism developmental potential. Totipotency is restricted to very early stages rather than being a property of every embryonic cell indefinitely.
Distinguish multipotent and unipotent cells — Multipotent stem cells can self-renew and generate a restricted range of related lineages. Unipotent progenitor or stem-cell populations generate one main differentiated lineage under the stated context. Potency describes the range of potential outcomes, not the total number of times any cell is guaranteed to divide or a claim that all mature heart cells routinely regenerate an entire heart.
Explain induced pluripotency — Appropriate transcription factors can reprogramme suitable adult somatic cells into induced pluripotent stem cells. This alters the gene-expression state rather than replacing the cell's entire genome with an embryo's DNA. Reprogramming efficiency, stability and differentiation control matter when evaluating potential use.
Evaluate stem-cell applications — Cells capable of producing needed tissue can support research or regenerative approaches, but controlled differentiation, integration, immune compatibility and tumour risk need evidence. Compare source, consent, embryonic status, cost and clinical outcomes. An ability to form a desired cell type in culture does not alone establish a safe effective treatment in an organism.
Transcription factors and epigenetic regulation
Explain transcription-factor control — Transcription factors bind appropriate regulatory DNA or interact with other components to influence transcription of target genes. Their activity can depend on signals, location and molecular modification. A transcription factor is usually a protein regulating gene activity, not the enzyme automatically joining every RNA nucleotide itself.
Trace an oestrogen-responsive pathway — A steroid hormone such as oestrogen can cross the cell membrane and bind an appropriate intracellular receptor. The activated receptor complex can act in transcriptional regulation at suitable DNA regions, altering target-gene expression. The outcome depends on receptor and regulatory context; not every cell responds identically or uses a membrane receptor for this steroid mechanism.
Define epigenetic change carefully — Epigenetic regulation involves changes in gene activity associated with features other than a changed DNA base sequence, some of which can persist through cell divisions. Environmental and developmental conditions can influence these states. Persistence in a cell lineage does not establish that every environmentally acquired mark is transmitted unchanged across multiple human generations.
Explain DNA methylation in context — In the course model, increased methylation, the addition of methyl (–CH₃) groups to DNA, at suitable gene-regulatory regions can reduce transcription by affecting access or recruitment of regulatory components. The result depends on location and context. Do not interpret the total methylation of an entire genome as a simple on-off score for every gene, or confuse adding methyl groups with substituting DNA bases.
Explain histone acetylation — Histones are proteins around which DNA is packaged; DNA together with its associated proteins forms chromatin. Acetylation, adding acetyl groups to suitable histone regions, is commonly associated with more accessible chromatin and increased transcriptional opportunity. Decreased acetylation can promote a less accessible state in the simplified model. Histone modification changes DNA packaging and regulation, not the order of the A, T, C and G bases.
Interpret expression evidence — Compare an actual measure such as transcript abundance, protein amount or cell behaviour between defined treatments and controls. Consider replication, baseline variation and alternative mechanisms. Increased mRNA does not guarantee an identical increase in functional protein because translation, processing and degradation can intervene.
RNA interference and cancer regulation
Explain sequence-specific RNA interference — Suitable small RNA molecules guide a protein complex to complementary target RNA. Depending on the system, binding can promote target-mRNA breakdown or inhibit its translation. The consequence is reduced expression of the target without necessarily altering the original DNA sequence; the small RNA is not translated into an enzyme that cuts every gene indiscriminately.
Use RNA interference as an investigation — Reducing a target's expression and observing a change can support a role for its product. Include suitable control RNAs, assess target reduction and consider unintended effects or compensation. A changed phenotype after one treatment does not by itself prove that the proposed target is the only affected pathway.
Distinguish benign and malignant tumours — A benign tumour remains localised in the basic comparison, while a malignant tumour can invade surrounding tissues and spread to other sites. Both involve abnormal growth, but location and effects vary. Benign does not mean incapable of harm, and malignancy is not defined merely by a tumour being large.
Compare growth-promoting and suppressing genes — Proto-oncogenes normally participate in regulated growth or division; activating changes can produce oncogenic activity promoting excessive proliferation. Tumour-suppressor genes normally help restrain growth, support repair or trigger appropriate responses to damage; loss of their function can remove safeguards. Cancer commonly involves multiple interacting changes rather than one universal mutation.
Connect epigenetic dysregulation to cancer — Inappropriate methylation can silence a tumour-suppressor gene, while altered regulation can increase expression of a growth-promoting gene. The direction and location of the change matter. Do not state that increasing methylation necessarily activates every oncogene or that all cancers have the same epigenetic pattern.
Evaluate oestrogen-related evidence — Some breast cancers depend on hormone-responsive growth pathways, so receptor status and hormonal signalling can be relevant to their biology and treatment. Evidence about one responsive subtype does not show that all breast cancers share the mechanism. Evaluate association, mechanism, treatment response and confounding from the supplied data.
Evaluate prevention and treatment hypotheses — Knowledge of a regulatory pathway can suggest targets for detection, prevention or therapy, but benefit requires evidence of selectivity, efficacy and harms. A molecular change correlated with cancer may be a driver, a consequence or a marker. Compare controlled outcomes rather than treating any laboratory reduction in cell growth as an established cure.
Genome projects and predicting proteins
Explain what genome sequencing supplies — A genome project determines DNA sequence information and supports identification of genes and other features. Sequence is a resource for hypotheses, not a direct record of which proteins are present in every cell at every time. Checking base-reading accuracy, assembling sequence fragments into longer sequences and annotating them to identify genes or other features are distinct steps, and computational predictions need appropriate validation.
Relate genomes to proteomes — Predicting protein sequences is more straightforward for well-characterised coding regions, but complex regulation, RNA processing, alternative transcripts and protein modification complicate the connection. A single genome can support many context-dependent proteomes. Counting predicted genes alone does not give the abundance or activity of each protein.
Use comparative sequence information — Sequence comparisons can identify candidate antigens or pathways for vaccine and drug research. A predicted surface protein is a candidate requiring tests of expression, accessibility, immune response and safety. Sequencing can guide experiments without automatically proving that every encoded antigen produces useful protection.
Evaluate sequence-data interpretation — Consider reference coverage, variation among individuals, annotation uncertainty and the environment when drawing conclusions. Similarity can suggest a shared function but is not complete functional proof. Methods evolve, so focus on what a supplied dataset and comparison actually establish rather than memorising an assumed permanent instrument design.
Producing recombinant DNA and transformed cells
Explain recombinant DNA — Recombinant DNA combines DNA sequences in a new arrangement, often to transfer a selected sequence into another cell. Broadly shared coding and gene-expression mechanisms permit expression in suitable hosts, but promoters, processing and cellular context must also be compatible. A transferred gene does not automatically function correctly in every organism without an expression strategy.
Obtain cDNA from expressed RNA — Reverse transcriptase can make complementary DNA using an mRNA template. Starting from appropriately processed eukaryotic mRNA can provide a sequence without the introns removed during splicing, useful when a host cannot perform the original splicing. Additional steps can generate double-stranded DNA for cloning.
Use restriction enzymes or synthesis — A restriction endonuclease cuts DNA at suitable recognition sites and may produce complementary overhangs or blunt ends, depending on the enzyme. A desired sequence can also be synthesised using known sequence information. Restriction cleavage alone does not guarantee the fragment contains the complete functional gene with all required regulatory regions.
Join a fragment to a vector — A vector, such as a suitable plasmid, carries inserted DNA into a host or supports its propagation. Compatible ends can associate by base pairing, and DNA ligase seals covalent backbone links. The enzyme does not create complementarity where unrelated overhangs do not match or guarantee that every plasmid receives the insert in the correct orientation.
Provide expression controls — An appropriate promoter supports transcription initiation, while a terminator region supports its ending in the intended expression system. Coding sequence, regulatory elements and orientation must suit the host and purpose. A marker reporting vector uptake is a different functional component from a promoter controlling the desired gene.
Transform and identify hosts — Introduce the vector into suitable host cells using an approved transformation method. Marker-based selection or screening can help identify cells with a vector or a particular insert, depending on the system. Distinguish successful uptake, correct insert presence and actual production of the desired functional protein: one test does not necessarily establish all three.
Amplify DNA in living cells — Culturing transformed hosts allows a suitable inserted DNA sequence to be copied as cells and vectors replicate. Maintain appropriate culture conditions and verify the desired construct rather than assuming every surviving colony is identical. This in vivo amplification differs from copying DNA in a cell-free PCR mixture.
PCR amplification and electrophoresis
Identify PCR requirements — Polymerase chain reaction uses template DNA, two suitable primers, short DNA sequences that provide starting points for copying, nucleotides and a thermostable (heat-resistant) DNA polymerase in appropriate reaction conditions. Primers define the region to be amplified by binding to opposite strands at flanking sites. Choosing primers is not the same as supplying an entire already synthesised copy of the target.
Trace PCR temperature stages — Heating separates template strands, cooling permits suitable primers to anneal, meaning bind to complementary template sequences, and a suitable extension temperature supports polymerase synthesis. Repeating these stages increases target copies. Exact temperatures depend on the system; explain the functions instead of treating one memorised number as correct for every enzyme and primer pair.Functional PCR stages rather than a universal temperature recipe: strand separation, suitable primer annealing and polymerase extension. Real efficiency and reagent limits qualify the ideal doubling model.
Calculate ideal amplification and its limits — In an idealised early PCR model, target copies double each cycle, so one starting double-stranded target gives 2ⁿ copies after n cycles. After 10 cycles this is 1024. Real reactions become limited by reagent availability, enzyme activity and other factors, so indefinite perfect doubling is a model rather than a guarantee.
Control PCR contamination and specificity — Include suitable negative and positive controls, separate preparation steps as required and use carefully chosen primers and conditions. Unwanted template can also be amplified, while poor primer binding can cause a false negative or unintended product. A band of roughly expected size supports but does not alone prove exact sequence identity.
Explain gel electrophoresis — DNA's negatively charged backbone causes fragments to move towards a positive electrode through a suitable gel. Under matched conditions, smaller fragments usually move farther than larger ones. A size ladder allows comparison; migration distance is not the number of bases read directly from a universal ruler independent of gel conditions.
Interpret fragment patterns — Compare sample lanes with a ladder and appropriate controls, distinguishing fragment size from band intensity. One visible band can contain multiple fragments of similar length, and an absent band can reflect a failed procedure rather than definite absence of an allele. Record which fragments the detection method actually reveals.
Genetic screening and personalised medicine
Explain probe hybridisation — A labelled single-stranded DNA probe can bind a complementary target sequence after suitable strand separation and hybridisation. The label helps detect the bound probe, while controlled conditions and washing support specificity. A probe locates matching sequence rather than independently sequencing every base in the entire genome.
Distinguish allele detection from prediction — Detecting a particular allele can identify a genotype or indicate a probability of an outcome, depending on the condition and evidence. Penetrance, the proportion of individuals with a genotype who show its associated phenotype, other genes and environmental factors can influence the relationship. A risk-associated allele is not automatically a certain diagnosis, and a negative result for one variant does not exclude every possible cause.
Explain genetic counselling and personalised approaches — Genetic information can support explanation of inheritance probabilities, reproductive choices or selection of an appropriate treatment where evidence links genotype to response. Counselling should communicate uncertainty and options rather than dictate one decision. Personalised medicine requires validated genotype-outcome relationships, not the claim that every person needs a unique untested drug.
Evaluate screening information — Consider sensitivity (how well a test identifies people with the target condition), specificity (how well it identifies people without it), prevalence (how common the condition is in the tested population), false results, clinical usefulness, informed consent, privacy and access. Predictive information may affect relatives as well as the tested individual. Distinguish the technical ability to detect a sequence from the benefit or justification of offering a screening programme.
DNA profiling, applications and ethical evaluation
Explain repeat-based variation — Variable number tandem repeats are regions in which a sequence unit occurs in differing copy numbers among alleles. Length variation at several loci can provide a highly discriminating profile. A profile from selected repeats is not the full genome, and related individuals can share alleles more often than unrelated individuals.
Trace a repeat-profiling workflow — Obtain a suitable sample, extract DNA, amplify selected regions where appropriate and separate or detect the resulting fragments using the specified method. Compare allele sizes across multiple loci with controls and suitable reference information. The exact procedure depends on the repeat system and assay; do not mix a historical whole-DNA method and a PCR-locus method without explaining which is being used.
Interpret inheritance in profiles — At an ordinary autosomal locus, a child receives one allele from each biological parent. Compare candidate profiles locus by locus, allowing for the stated assay and exceptions. A matching band at one locus is weak evidence; multiple consistent informative loci strengthen an inference, while genuine incompatibility needs careful assessment of technical error and biological context.
Evaluate forensic matches — A matching profile is evidence whose strength depends on the loci, population frequencies, relatedness, sample quality and interpretation. Contamination, mixed samples and transfer can affect conclusions. The probability of a profile match is not identical to the probability that a person committed an offence, so distinguish molecular identification from the wider event claim.
Apply profiles beyond forensics — Repeat or other genetic markers can support pedigree checks, conservation genetics, breeding programmes and assessment of variation. Select a method that answers the actual question and preserves useful diversity where appropriate. A profile useful for identity does not automatically diagnose every inherited disorder.
Relate gene transfer to therapy — A gene-therapy strategy can aim to supply, alter or regulate genetic information in suitable cells to change a disease mechanism. Delivery, target-cell survival, duration of expression, immune response and unintended effects require evaluation. Somatic changes ordinarily affect the treated individual, whereas heritable changes raise different issues for future generations.
Evaluate recombinant technologies in context — Compare the proposed benefit with evidence about ecological effects, food or medicine access, ownership, cost, consent and uncertainty. A modified crop, microbial factory and somatic therapy have different exposures and decision contexts. Assess specific mechanisms and data rather than treating all genetic modification as one uniformly beneficial or harmful intervention.
Synoptic reasoning and written assessment
Plan a relevant synoptic essay — Paper 3 includes a 25-mark essay chosen from two titles. Identify the precise biological theme, select relevant examples across the course and plan connected explanations. For a theme about membranes, a plan could connect compartmentalised ATP synthesis, transport, synaptic communication and kidney water recovery, but each paragraph must explain its relevance to the actual title rather than simply mention a membrane.
Develop explanatory paragraphs — Start with a relevant biological claim, explain its mechanism accurately, then connect that mechanism explicitly to the essay theme. Integrate correct terminology and qualified examples. Breadth without explanation becomes a list, while one elaborate example alone may not demonstrate the required course-wide understanding.
Use unfamiliar information critically — Separate facts supplied in a passage from conclusions inferred using biological knowledge. Check comparison groups, units, denominators, sample size and uncertainty, and quote or calculate relevant numerical evidence. A plausible mechanism does not remove the need to evaluate the actual data or distinguish correlation from a tested cause.
Explain practical choices rather than list equipment — For a proposed investigation, connect the independent variable to a measurable dependent outcome, justify controls and replication and state a reproducible method. Distinguish random error from systematic bias and propose improvements addressing the identified limitation. Completing a knowledge quiz does not demonstrate the practical competencies assessed through actual work.
Communicate calculations and conclusions — State the relationship, substitute consistent units, show intermediate steps and give a suitably rounded answer with units. Distinguish an absolute change, a percentage change and a change in percentage points. Link any final conclusion to the evidence and its limits rather than merely restating the question.
Keep genuine practical evidence — The practical endorsement depends on appropriate evidence of actual practical skills and centre assessment. Use these notes and tasks to prepare and reflect, while retaining authentic records of methods, observations, analysis and decisions. Neither an online score nor a prepared checklist certifies that a practical procedure has been performed.
Test yourself
50 questions · Random sets of 10. These quick checks support revision; practise longer explanations and justified judgements too.
Mr Kidman's Classroom
