Biology • Year 12 • Module 6 • Lesson 11
Biodiversity Change Caused by Genetic Techniques
Apply the three-level biodiversity framework to three current Australian genetic-technology debates: cane toad gene drives, GMO crops and Tasmanian devil rescue cloning.
1. Case study — cane toad gene drive proposals
Cane toads (Rhinella marina) were introduced into Queensland in 1935 and have since spread across northern Australia, where they poison native predators that bite them (e.g. quolls, freshwater crocodiles). One proposed solution is a gene drive: a genetic technique that biases inheritance so that an introduced trait (e.g. female-only sterility, or a trait that suppresses bufotoxin production) spreads through the wild toad population faster than normal Mendelian inheritance would allow. 9 marks
1.1 Identify the biodiversity level (genetic, species or ecosystem) at which the gene drive is intended to operate on the cane toad itself, and explain why. 2 marks
1.2 Explain one positive biodiversity effect the proposed gene drive could have for native Australian species at the species and/or ecosystem level. 3 marks
1.3 Identify two uncertain or negative biodiversity effects of releasing the gene drive. Use lesson terminology (e.g. "non-target species", "ecological interactions", "unpredictable"). 2 marks
1.4 Using the lesson's framing, write a one-sentence balanced judgement about this proposal — your sentence must reject both "this is automatically good" and "this is automatically bad". 2 marks
2. Interpret GMO crop data — biodiversity vs productivity
A research team compared three cotton-growing regions in northern New South Wales over five seasons after the widespread adoption of an insect-resistant GM Bt cotton. They recorded average yield (bales / ha), the number of cotton genotypes planted across the region, and the number of non-target arthropod species (e.g. beneficial insects, ground beetles) in the surrounding hedgerows. 8 marks
| Region | Cotton yield (bales / ha) | Genotypes planted | Non-target arthropod species in hedgerows |
|---|---|---|---|
| Pre-GM baseline (all regions) | 6.4 | 11 | 27 |
| Region A — full Bt adoption | 10.8 | 2 | 31 |
| Region B — partial Bt adoption | 9.1 | 5 | 29 |
| Region C — no Bt adoption | 6.2 | 9 | 26 |
Stylised illustrative data, after Whitehouse et al. (2007), Bt cotton in Australia: a decade of adoption.
2.1 Describe what happens to yield as Bt cotton adoption increases. 1 mark
2.2 Describe what happens to cotton genotypes planted as Bt cotton adoption increases. State which biodiversity level this is. 2 marks
2.3 A farmer reads this table and says: "Bt cotton increases biodiversity because hedgerow arthropod species went up". Use the lesson's framing to explain why this single-level conclusion is too simple. 3 marks
2.4 Suggest one further measurement the team could take in Region A to better evaluate the genetic-level biodiversity effect of Bt cotton. 2 marks
3. Cause-and-effect — Tasmanian devil rescue cloning
The Tasmanian devil (Sarcophilus harrisii) is threatened by Devil Facial Tumour Disease (DFTD), a transmissible cancer. Wild populations have crashed to ~10–20% of pre-DFTD numbers and show extremely low genetic diversity at immune-related genes (MHC). One proposed rescue uses somatic cell nuclear transfer (SCNT) cloning from preserved tissue of an MHC-diverse devil that died before DFTD spread, in order to reintroduce its alleles to the wild population. 7 marks
Complete the cause-and-effect chain below by writing the missing effects into the blank boxes. Then write the overall outcome.
| Cause (given) | Effect (write your answer) |
|---|---|
| SCNT cloning produces a new individual carrying the diverse MHC alleles of the deceased devil. | |
| The clone is released into the wild population and breeds with surviving wild devils. | |
| Offspring inherit the rare MHC alleles previously missing from the population. | |
| Some offspring carry MHC alleles that allow their immune system to detect DFTD cells. |
Overall outcome (so…): What does this chain suggest for the long-term continuity of the Tasmanian devil species, and at which biodiversity level is the main benefit? 3 marks
4. Compare-and-contrast — three biotechnologies, three biodiversity outcomes
Complete the comparison table below for the three case studies in this worksheet. 9 marks (3 columns × 3 rows)
| Criterion | Cane toad gene drive | GM Bt cotton | Tasmanian devil SCNT cloning |
|---|---|---|---|
| Main biodiversity level targeted | |||
| One clear biodiversity benefit | |||
| One clear biodiversity cost or uncertainty |
Q1.1 — Level for gene drive in the cane toad (2 marks)
The gene drive operates at the genetic level within the cane toad species [1]: it biases the inheritance of specific alleles (e.g. a sterility or non-toxic allele), changing the allele frequencies inside the cane toad population [1]. (Accept "genetic / species" if students argue that the technique is designed to ultimately reduce cane toad species abundance in Australia.)
Q1.2 — Positive biodiversity effect for native species (3 marks)
If the gene drive successfully reduces cane toad numbers, native predators that are currently poisoned by cane toad bufotoxin (quolls, goannas, freshwater crocodiles) experience reduced mortality [1]. This supports the persistence of those native species (species-level benefit) [1] and can also restore predator–prey interactions and food-web structure across northern Australian ecosystems (ecosystem-level benefit) [1].
Q1.3 — Uncertain / negative effects (2 marks)
Award 1 mark each (max 2) for any two of: (a) the drive could spread to non-target populations or related species via hybridisation or accidental escape; (b) suppressing cane toads in some areas could create unexpected ecological interactions (e.g. predators that have already adapted to cane toads as prey could lose a food source); (c) gene drives are difficult to reverse, so unintended ecological outcomes may be hard to undo; (d) effects on long-term ecosystem-level dynamics across complex northern Australian habitats are inherently difficult to predict perfectly.
Q1.4 — Balanced judgement sentence (2 marks)
Sample: "A cane toad gene drive may support native species and ecosystem-level recovery, but it may also affect non-target species and is difficult to reverse, so its biodiversity effect depends on what scale and which level we measure." [1 — uses balanced "may / depends on" language; 1 — names at least two levels (e.g. species + ecosystem) rather than one]. Reject one-sided answers such as "this will save Australia's wildlife".
Q2.1 — Yield trend (1 mark)
Yield rises with Bt adoption (6.2 bales/ha in Region C → 9.1 in Region B → 10.8 in Region A) — roughly a 74% increase from no-Bt to full Bt at the same baseline. [1]
Q2.2 — Cotton genotypes planted (2 marks)
The number of cotton genotypes planted falls as Bt adoption increases (11 → 9 → 5 → 2). [1] This is a fall in genetic-level biodiversity within the crop. [1]
Q2.3 — Why "biodiversity went up" is too simple (3 marks)
The farmer is only looking at one level — hedgerow arthropod species (an ecosystem / species-level proxy) [1]. The same table shows that genetic-level biodiversity within the cotton crop has dropped sharply (from 11 to 2 genotypes) [1]. The lesson's whole point is that biodiversity must be judged at all three levels: this case is a mixed outcome — positive at the hedgerow / ecosystem level, negative at the genetic level inside the crop — not a clean "biodiversity went up" claim [1].
Q2.4 — Further measurement for genetic-level effect (2 marks)
Sample: directly measure allele diversity (heterozygosity) at marker loci across the cotton plants in Region A [1] and compare with the pre-GM baseline so that any drop in within-crop genetic diversity is detected even when only 2 named genotypes are sown [1]. (Accept "measure number of unique alleles at a defined marker panel" or "compare allele richness between Region A and Region C".)
Q3 — Cause-and-effect chain (7 marks)
1 mark per correctly completed effect (max 4):
- Cause 1 → Effect: the clone carries MHC alleles that have been lost from the surviving wild population.
- Cause 2 → Effect: those MHC alleles are reintroduced into the wild gene pool through reproduction.
- Cause 3 → Effect: genetic diversity at MHC in the wild population increases.
- Cause 4 → Effect: these offspring have a better chance of surviving infection, so the population's resilience to DFTD rises.
Overall outcome (3 marks): the chain raises the chance that the Tasmanian devil persists as a species despite DFTD [1]; the main benefit is at the genetic level (restoring lost MHC allele variation) [1] but it translates into a species-level benefit (continuity of the species) [1]. This is the lesson's Card 3 use of biotechnology: conservation genetics supporting a threatened population.
Q4 — Comparison table (9 marks)
Award 1 mark per cell (max 9) for biologically defensible answers. Sample completion:
| Criterion | Cane toad gene drive | GM Bt cotton | Devil SCNT cloning |
|---|---|---|---|
| Main biodiversity level targeted | Genetic (within toad); intended species/ecosystem benefit for native fauna | Genetic (within crop) — drives toward fewer genotypes | Genetic (restoring MHC alleles in wild devils) |
| One clear biodiversity benefit | Native predators (e.g. quolls) protected from bufotoxin → species + ecosystem recovery | Less broad-spectrum insecticide use can support hedgerow arthropods (ecosystem level) | Restores lost MHC variation → supports species continuity |
| One clear biodiversity cost or uncertainty | Drive may spread to non-target populations; ecological effects difficult to predict | Crop genetic diversity falls (few genotypes dominate the landscape) → monoculture risk | Population still relies on ongoing human management; small founder genetic contribution from a single individual |
Mark generously for biologically valid alternatives. Award full 9 only if the student correctly identifies a different level for the cost vs. the benefit on at least two of the three cases (i.e. the student is doing multi-level analysis rather than single-level reasoning).