Biology • Year 12 • Module 6 • Lesson 15
Cloning — Whole Organism and Gene Cloning
Apply cloning theory to real numbers: the Dolly experiment success rate, the Tasmanian thylacine cloning attempts, and a worked case on gene cloning of human insulin.
1. Dolly the sheep — what the real numbers say about effectiveness
Dolly the sheep (born 5 July 1996, Roslin Institute, Edinburgh) was the first mammal produced by somatic-cell nuclear transfer (SCNT) from an adult body cell. The table below summarises the published efficiency of that experiment. 9 marks
| Stage of the Dolly experiment | Number | % of previous stage |
|---|---|---|
| Reconstructed embryos created (donor nucleus fused with enucleated egg) | 277 | — |
| Embryos that developed enough to be implanted into surrogate ewes | 29 | ≈ 10.5% |
| Pregnancies established | 13 | ≈ 44.8% of implanted |
| Live lambs born | 1 (Dolly) | ≈ 7.7% of pregnancies |
| Live lambs from total reconstructed embryos | 1 | ≈ 0.36% |
Data: Wilmut et al. (1997), Nature 385: 810–813 ("Viable offspring derived from fetal and adult mammalian cell nuclei").
1.1 Express the overall success rate of the Dolly experiment as a ratio (embryos : live lambs) and as a percentage. 2 marks
1.2 Identify two stages of the workflow where the largest drop-offs occurred, and suggest one biological reason for each loss. 4 marks
1.3 A newspaper article in 1997 claimed: "Dolly proves that cloning is now an efficient way to copy mammals." Use the data to evaluate that claim in 2–3 sentences. 3 marks
2. SCNT efficiency across species — bar graph
The figure below shows the published live-birth efficiency of somatic-cell nuclear transfer for several mammalian species, expressed as live births per 100 reconstructed embryos. 6 marks
Indicative figures compiled from published SCNT studies (after Wilmut et al. 1997; Wakayama et al. 1998; Polejaeva et al. 2000; Lee et al. 2005; Liu et al. 2018). Rounded for teaching use.
2.1 Identify the species with the highest and lowest live-birth efficiency, and state both values. 2 marks
2.2 Even the highest bar in the graph is only about 2%. Use this to evaluate the lesson's claim that "whole-organism cloning has low efficiency". 2 marks
2.3 A biotech start-up uses this graph to advertise: "Cloning is more reliable in some species, so our service is safe." Identify one weakness in that advertisement. 2 marks
3. The Tasmanian thylacine — should we try to clone an extinct animal?
The thylacine (Thylacinus cynocephalus) was a marsupial carnivore endemic to Tasmania. The last known animal died at Hobart Zoo in 1936. Read the timeline, then answer the questions. 9 marks
1936 — Last confirmed thylacine ("Benjamin") dies in Hobart Zoo. The species is later declared extinct.
1999 — Australian Museum (Sydney) launches a project to clone the thylacine using DNA recovered from a preserved 1866 pup specimen.
2002 — Project reports successful PCR amplification of fragments of thylacine DNA, but the DNA is heavily degraded.
2005 — Australian Museum officially abandons the cloning project, citing degraded DNA and the absence of a viable cell.
2008 — Pask et al. (PLOS ONE) insert a thylacine gene (Col2a1 enhancer) into mouse embryos using gene-cloning techniques; the gene is shown to be functional in mouse cartilage.
2022 — University of Melbourne + Colossal Biosciences announce a new project aiming to use gene-editing of a related living marsupial (fat-tailed dunnart) plus an artificial surrogate, NOT classical SCNT, to attempt "de-extinction".
3.1 Explain why the 1999–2005 Australian Museum project was unable to use somatic-cell nuclear transfer to clone the thylacine, even with thylacine DNA available. 3 marks
3.2 The 2008 Pask et al. study used gene cloning, not whole-organism cloning. Explain why gene cloning was a more achievable goal for that team, with reference to the lesson's distinction between the two technologies. 3 marks
3.3 Even if the 2022 project produces a live animal, why would the lesson's "phenotype is not guaranteed" warning still apply? Give one specific biological reason. 3 marks
4. Apply gene cloning to a real scenario — human insulin
Before the 1980s, insulin used to treat diabetes was extracted from the pancreases of pigs and cattle, with about 1 kg of insulin requiring around 8,000 kg of pancreas tissue. In 1982 Eli Lilly's "Humulin" became the first marketed therapeutic produced by gene cloning: the human insulin gene was inserted into a bacterial plasmid, transferred into E. coli host cells, and the cells cultured to produce human insulin in industrial fermenters. 6 marks
4.1 Identify the vector and the host cell used in the Humulin process, and state the role of each. 2 marks
4.2 Explain two reasons why gene cloning is more effective than the pre-1980s animal-extraction method for producing insulin. 2 marks
4.3 Using the Humulin example, justify the lesson's claim that "gene cloning's effectiveness is often easier to justify than whole-organism cloning's effectiveness" in 1–2 sentences. 2 marks
Q1.1 — Overall success rate of Dolly (2 marks)
Ratio is approximately 277 : 1 reconstructed embryos to live lambs [1]. As a percentage that is 1/277 ≈ 0.36% (accept 0.3–0.4%) [1].
Q1.2 — Largest drop-offs (4 marks)
Largest losses occurred (i) between reconstructed embryos (277) and embryos suitable for implantation (29) — a ~89.5% loss [1]; and (ii) between pregnancies established (13) and live lambs (1) — a ~92% loss [1]. Biological reasons (any one each, 1+1 marks): embryos fail to reprogram the donor nucleus and so stall in early cleavage; many implanted embryos fail to develop normally because of epigenetic abnormalities in the donor DNA; many pregnancies miscarry due to placental defects ("large offspring syndrome"); developmental failures during gestation due to inappropriate gene expression from the somatic donor nucleus.
Q1.3 — Evaluate the 1997 newspaper claim (3 marks)
The claim is not supported by the data [1]. Producing one live lamb from 277 reconstructed embryos (≈0.36% success) is the opposite of an efficient process — most attempts failed at one of several stages, including over 90% loss between pregnancy and live birth [1]. The data shows that whole-organism cloning is biologically possible, but its effectiveness as a routine "way to copy mammals" was extremely low, exactly the limitation the lesson highlights in Card 2 [1].
Q2.1 — Highest and lowest SCNT efficiency (2 marks)
Highest: cow ≈ 2.0% [1]. Lowest: sheep ≈ 0.4% (Dolly's species) [1]. (Macaque at 0.6% is also accepted as second-lowest reasoning.)
Q2.2 — "Whole-organism cloning has low efficiency" (2 marks)
The claim is strongly supported [1]. Even the best-performing species (cow, dog) require ≈50 reconstructed embryos to produce one live birth, and most species lose 98–99% of attempts somewhere in the workflow — well outside what is typically called an "efficient" biological process [1].
Q2.3 — Weakness in the start-up's advertisement (2 marks)
The advertisement conflates "more reliable than other species" with "reliable" [1]. Even cow SCNT at ~2% still means ~98% of attempts fail; the graph does not say anything about the health, longevity or phenotype of the surviving clones — so "safe" cannot be justified from these data [1].
Q3.1 — Why SCNT failed for the thylacine project (3 marks)
SCNT requires a viable donor cell with an intact nucleus that can be reprogrammed inside the enucleated egg [1]. The thylacine DNA available in 1999 came from a 19th-century pup preserved in ethanol — the DNA was fragmented and degraded, with no living cell or intact nucleus to transfer [1]. PCR could amplify short fragments, but you cannot reconstruct a whole, functioning, ordered genome to drive embryonic development from those fragments, so SCNT was not a feasible technique with the available material [1].
Q3.2 — Why gene cloning was achievable (3 marks)
Gene cloning targets a single selected DNA sequence and inserts it into a vector for replication in a host cell — the goal is narrow and the technique tolerates short DNA fragments [1]. Pask et al. only needed one functional region of one thylacine gene (the Col2a1 enhancer), which could be amplified from degraded DNA and ligated into a vector [1]. Whole-organism cloning would have required reconstructing the entire genome inside a viable egg — a much harder organism-level goal that was impossible with the available degraded material, which is why the team chose the gene-level approach [1].
Q3.3 — "Phenotype not guaranteed" applied to the 2022 project (3 marks)
Even if gene-edited dunnart cells produce a live "thylacine-like" animal, its phenotype is not guaranteed to match a real thylacine [1]. The marsupial surrogate provides a different uterine environment from a real thylacine mother; epigenetic reprogramming of the edited nucleus may be incomplete; and many phenotypic traits (size, coat pattern, behaviour, gut microbiome) depend on developmental and environmental conditions, not just nuclear DNA [1]. So we may produce an organism with thylacine-like DNA at some loci, but not a true ecological or behavioural restoration of the species — exactly the lesson's warning that genotype copying does not guarantee identical phenotype [1].
Q4.1 — Vector and host in Humulin (2 marks)
Vector: bacterial plasmid — carries the inserted human insulin gene into the host and replicates inside it [1]. Host cell: E. coli — receives the recombinant plasmid, divides repeatedly to produce many copies of the gene, and expresses the gene to produce human insulin protein, which is harvested from culture [1].
Q4.2 — Two reasons gene cloning beats animal extraction (2 marks)
Any two of: (a) the insulin produced is identical to the human protein rather than slightly different pig/cow insulin, reducing immune reactions in patients; (b) production scales by simply growing more bacteria in fermenters rather than slaughtering thousands of animals; (c) it is far cheaper per kilogram and not limited by livestock supply; (d) the source is safer — no risk of pathogen contamination from animal pancreas tissue [1 each, max 2].
Q4.3 — Gene cloning's effectiveness vs whole-organism cloning's (2 marks)
The Humulin process has a narrow, measurable goal (produce many copies of the human insulin gene and its protein) and bacterial fermentation routinely achieves this at industrial scale [1]. Whole-organism cloning has a much broader goal — produce a developmentally viable organism — and the Dolly data (≈0.36% success) shows that achieving that goal at acceptable rates is far harder. The narrower, well-defined goal is exactly why gene cloning's effectiveness is easier to justify [1].