HSC Exam Practice

Sample response. Gene cloning is the production of many identical copies of a selected DNA sequence by inserting it into a vector (such as a plasmid) and replicating it in a host cell.

Marking notes. 1 mark for identifying that gene cloning copies a selected DNA sequence (gene-level, not organism-level); 1 mark for naming the vector + host cell mechanism by which the copying occurs.

Sample response. Whole-organism cloning copies the nuclear genotype of an entire organism, using somatic-cell nuclear transfer (SCNT) in which a nucleus from a donor body cell is inserted into an enucleated egg and the reconstructed cell is implanted into a surrogate to develop. Gene cloning copies only a selected DNA sequence (a single gene or fragment) by inserting it into a vector such as a bacterial plasmid and replicating it in a host cell. The two technologies therefore differ both in the level of biology copied (whole organism vs single gene) and in the cellular technique used (nuclear transfer + surrogate vs vector + host cell).

Marking notes. 1 mark for level of biology contrast (whole-organism / nuclear genotype vs single DNA sequence); 1 mark for naming the technique on each side (SCNT / nuclear transfer vs vector + host cell); 1 mark for explicitly stating that they are different technologies, not the same process at different scales.

Sample response. A vector (commonly a bacterial plasmid or a virus) carries the chosen target DNA sequence into a host cell. The host cell receives the recombinant vector and replicates it many times as the host cell itself divides; in many applications the host also expresses the inserted gene to produce a useful protein. Together they convert one starting gene into many identical copies, plus optionally many copies of its encoded product.

Marking notes. 1 mark for vector as DNA carrier into the host; 1 mark for host cell as the site of replication / division; 1 mark for the connection between the two (host cell division produces many copies of the recombinant DNA).

Sample response. In somatic-cell nuclear transfer, an egg cell is first taken and its own nucleus is removed (enucleated), so the egg contributes no nuclear DNA. A nucleus from a donor body (somatic) cell is then inserted into the enucleated egg, supplying the genetic information of the desired donor. The reconstructed cell is stimulated (electrically or chemically) to begin dividing; if it develops into an early embryo, the embryo is implanted into a surrogate, where it may continue development to birth.

Marking notes. 1 mark for removal of the egg nucleus (enucleation); 1 mark for transfer of the donor somatic nucleus into the enucleated egg; 1 mark for stimulation of division and implantation into a surrogate. All three steps required for full marks.

Sample response. Phenotype is shaped by genotype, by gene expression (which can be influenced by epigenetic state and the cytoplasmic environment of the egg), and by environmental conditions during development and life. A clone shares its donor's nuclear DNA but is gestated in a different surrogate environment, may carry mitochondrial DNA from the egg donor, and grows up in different conditions. The donor nucleus may also be incompletely reprogrammed by the new egg cytoplasm, producing developmental and ageing differences. Therefore identical nuclear genotype does not guarantee identical phenotype, only similar nuclear genetic information.

Marking notes. 1 mark for stating that phenotype depends on genotype and environment / development; 1 mark for identifying at least one specific source of variation (mitochondrial DNA from the egg, surrogate environment, epigenetic / nuclear-reprogramming differences); 1 mark for explicitly concluding that identical genotype does not guarantee identical phenotype.

Sample response (a). Overall success rate = 1 / 277 × 100 = 0.36% (accept 0.3–0.4%).

Sample response (b). Live-birth efficiency is below 2.5% in every species shown. Cow is highest at ≈2.0%, followed by dog (≈1.8%) and mouse (≈1.5%). The remaining species — pig (≈1.0%), macaque (≈0.6%) and sheep (≈0.4%) — sit at or below 1%. Across the dataset, efficiency varies by roughly a factor of five between the best and worst species, but no species exceeds 2% live births per reconstructed embryo.

Sample response (c). The data strongly support the lesson's claim. The Dolly experiment itself produced only 1 live lamb from 277 attempts (≈0.36%), and the inter-species graph shows that even the most efficient species, the cow at ≈2.0%, still requires roughly 50 reconstructed embryos for one live birth. For a process to be described as routinely effective it would need success rates an order of magnitude higher; at 1–2% efficiency, whole-organism cloning consumes very large numbers of embryos and surrogates per live offspring, which is exactly the "low effectiveness" the lesson describes.

Marking notes. Part (a) — 1 mark for the correct calculation (1/277 × 100 ≈ 0.36%). Part (b) — 1 mark for a correctly described overall trend (all species < 2.5%; range from 0.4% to 2.0%); 1 mark for ranking at least three species or noting that no species exceeds 2%. Part (c) — 1 mark for citing at least one specific value (e.g. Dolly 0.36%, cow 2.0%, ~50 embryos per live birth); 1 mark for linking the value to "low efficiency"; 1 mark for explaining what "routinely effective" would require (much higher success rates) so the data justify the lesson's claim.

Sample response. Effectiveness in biotechnology is the extent to which a process achieves its intended purpose, judged against success rate, fitness-for-purpose and limitations — not simply whether copying occurred. Evaluated this way, the two cloning technologies have very different effectiveness profiles. Whole-organism cloning, using somatic-cell nuclear transfer, copies the entire nuclear genotype of an organism. The Dolly experiment (Wilmut et al., 1997) achieved only ≈0.36% live births per reconstructed embryo, and even the best-performing species (cow ≈2%) still requires roughly 50 attempts per live birth. A real application — preservation of an elite dairy-cow genotype, or production of transgenic founder animals such as the antithrombin-producing sheep developed by PPL Therapeutics — is fit-for-purpose because each live clone has high value and a 1–2% rate is acceptable for low-volume, high-value applications. Whole-organism cloning is therefore effective for narrow, high-value goals but ineffective as a general-purpose mammal-replication service, and it cannot guarantee identical phenotype because development and environment also shape outcomes. Gene cloning, in contrast, copies a selected DNA sequence using a vector (e.g. a bacterial plasmid) and a host cell (e.g. E. coli). The 1982 introduction of recombinant "Humulin" human insulin is the standard real-world example: global insulin production has scaled from about 2 t per year (animal pancreas extraction) to about 40 t per year, supplying more than 200 million patients with a product that exactly matches the human sequence. The goal of gene cloning — produce many copies of one defined sequence — is narrow and biologically well-characterised, so high success rates are achievable with bacterial fermentation. The key driver of this effectiveness gap is the goal itself: whole-organism cloning's goal (produce a viable developing organism) is far broader and biologically harder than gene cloning's goal (replicate one defined DNA sequence), which is exactly why the lesson insists that effectiveness be assessed against purpose rather than treated as a blanket property of "cloning". Overall, gene cloning is highly effective for specific, well-defined biotechnology goals such as therapeutic-protein production, while whole-organism cloning is biologically significant but practically limited — effective only for narrow, high-value applications and never as a routine reliable copy-paste of mammals. The claim that cloning is "always effective" or "never effective" is rejected: effectiveness depends on what the technology is asked to do.

Marking notes. 1 mark — defines or implicitly applies "effectiveness" as goal-relative (success rate + fitness-for-purpose + limitations). 1 mark — correctly outlines whole-organism cloning (nuclear genotype, SCNT, enucleated egg, surrogate). 1 mark — correctly outlines gene cloning (selected DNA sequence, vector, host cell, replication / expression). 1 mark — uses a valid real-world example of each technology with at least one specific quantitative or biological detail (e.g. Dolly ≈0.36%; cow SCNT ≈2%; Humulin scale 2 → 40 t/year or human-sequence fidelity). 1 mark — identifies at least one limitation of whole-organism cloning beyond low efficiency (e.g. placental abnormalities / "large offspring syndrome", phenotype not guaranteed, ethical or welfare concerns). 1 mark — explains the effectiveness gap using the narrow-vs-broad goal distinction (gene cloning's goal is narrow and well-defined; whole-organism cloning's goal is much harder). 1 mark — reaches an explicit assessment that rejects "always effective / never effective" and frames effectiveness as purpose-dependent.