Biology • Year 12 • Module 6 • Lesson 13
Current Genetic Technologies That Induce Genetic Change
Build HSC Band 5–6 extended-response technique on the three lesson categories — reproductive control, DNA copying / insertion, and whole-organism cloning — by working through two data-rich evaluation tasks.
1. Data + scenario — adoption of genome-editing technologies in laboratories worldwide (Band 5–6)
8 marks Band 5–6
Scenario. Three site-specific genome-editing technologies — zinc-finger nucleases (ZFNs, 2003), TALENs (2011) and CRISPR-Cas9 (2012) — all induce DNA-level genetic change by making targeted double-strand breaks. The graph below shows the number of peer-reviewed publications per year that use each technology in mammalian-cell research from 2008 to 2022. By 2023, CRISPR-Cas9 had been adopted by major laboratories across more than 60 countries; ZFNs and TALENs continue to be used for niche applications. In December 2023, the US FDA approved Casgevy, the first CRISPR-Cas9 therapy, for sickle-cell disease — using the same BCL11A enhancer target that an earlier ZFN trial had also pursued.
Trend constructed from PubMed indexed counts for "ZFN / TALEN / CRISPR-Cas9 + mammalian cell" 2008–2022; magnitudes reflect commonly reported orders of magnitude.
Q1. Analyse and evaluate, using the data and lesson terminology, why CRISPR-Cas9 has been so rapidly adopted as the dominant DNA-editing technology in mammalian-cell research, and assess the consequences for the way HSC students should describe "current genetic technologies that induce genetic change". In your response you must:
- Define genetic technology and place CRISPR-Cas9, TALENs and ZFNs within the lesson's three-category framework.
- Describe two specific features of the graph (with figures) that support your analysis.
- Compare the three technologies on at least three criteria (e.g. design time, cleavage efficiency, off-target activity, year of introduction).
- Use the Casgevy / sickle-cell context as a worked example linking adoption to clinical or agricultural outcomes.
- Reach an evidence-based judgement on whether "DNA editing" should be treated as a single category in an HSC response.
2. Data + scenario — global adoption of transgenic Bt cotton (Band 5–6)
8 marks Band 5–6
Scenario. Bt cotton is a transgenic crop produced by recombinant DNA technology: a cry gene from the soil bacterium Bacillus thuringiensis is inserted into the cotton genome so that the plant expresses an insecticidal protein in its leaves and bolls, killing key boll-worm pests. Bt cotton was commercialised in 1996. The table below shows the percentage of cotton-growing area planted with Bt cotton in three major producing countries from 2002 to 2019 (ISAAA brief 55, 2019), alongside reported pesticide-spray reductions and ongoing concerns about pest resistance.
| Country | % cotton area Bt (2002) | % cotton area Bt (2010) | % cotton area Bt (2019) | Pesticide spray reduction (typical) | Notable issue reported |
|---|---|---|---|---|---|
| USA | ~ 35 % | ~ 73 % | ~ 95 % | ~ 50 % (vs pre-Bt baseline) | Local Helicoverpa zea resistance reported by 2014 |
| India | < 1 % | ~ 86 % | ~ 94 % | ~ 40–50 % | Pink bollworm resistance to Cry1Ac confirmed by 2010 |
| China | ~ 51 % | ~ 68 % | ~ 95 % | ~ 60 % in early years; reduced advantage over time | Secondary pest (mirid bug) outbreaks from 2007 |
Adoption figures: ISAAA Brief 55 (2019). Resistance and secondary-pest reports: Tabashnik et al. (2013) Nature Biotechnology 31: 510–521; Lu et al. (2010) Science 328: 1151–1154.
Q2. Evaluate, using the data, the claim that "recombinant DNA technology is the most important current genetic technology that induces genetic change because, unlike reproductive technologies, it can introduce a brand-new trait that does not already exist in the species." Assess this claim against the lesson's framing of genetic technologies. In your response you must:
- Define recombinant DNA technology and transgenic organism using lesson terminology.
- Identify what is "induced" in Bt cotton — at what biological level — and contrast this with what artificial pollination would have produced from the same starting cotton population.
- Cite at least three specific data points from the table to support your analysis.
- Identify at least two real limitations shown in the data (e.g. pest resistance, secondary pests, declining advantage).
- Reach a judgement that explicitly rejects the idea of a single "most important" technology and frames choice as purpose-dependent, using the lesson's framework.
Q1 — Sample Band 6 response (8 marks), annotated
A genetic technology is a technology used to analyse, manipulate or direct inheritance and genetic change. Within the lesson's three-category framework, ZFNs, TALENs and CRISPR-Cas9 all sit in the DNA-level category: they induce a targeted change in the DNA sequence of cells. They differ from reproductive technologies (artificial insemination, artificial pollination), which only direct gamete combination, and from whole-organism cloning, which acts at the cellular and developmental level. [1 — defines and categorises]
The publication-count graph makes two features clear. First, CRISPR-Cas9 publications grew from essentially zero in 2012 to over 4500 per year by 2022, dwarfing both ZFNs (~50–200 per year, roughly flat) and TALENs (peaking near 600 in 2014 then declining). Second, the post-2012 CRISPR curve is steeper than the TALEN curve ever became, showing not just adoption but accelerating adoption. [1 — two graph features with figures]
Three criteria explain this. (i) Design time: CRISPR reagents take days because targeting uses a 20-nt guide RNA; ZFNs require months of protein engineering; TALENs require weeks. (ii) Cleavage efficiency: CRISPR achieves ~40–80% editing in mammalian cells compared with ~20% for TALENs and ~10% for ZFNs. (iii) Off-target activity: TALENs reduced the off-target problem relative to ZFNs, but CRISPR — once engineered with high-fidelity variants and validated guides — produces comparable on-target performance with much faster iteration. [1 — three criteria; 1 — figures correctly used]
The lesson's "what changes, where, why" framework explains why this matters in practice. The 2023 FDA approval of Casgevy targeted the same BCL11A enhancer that an earlier ZFN trial had also pursued — but CRISPR's ~80% editing in patient haematopoietic stem cells, combined with rapid reagent iteration during preclinical development, made the therapeutic outcome reproducible enough to cross the regulatory bar first. ZFN-based approaches remain in development for the same indication. [1 — Casgevy as a worked example with mechanism, not just a name-drop]
The implication for HSC responses is direct. "DNA editing" cannot be collapsed into a single undifferentiated technology in a Band 5–6 answer — within the DNA-level category, ZFNs, TALENs and CRISPR-Cas9 differ in efficiency by an order of magnitude and in design time by roughly a factor of twenty. A strong response identifies CRISPR-Cas9 as a specific named DNA-editing technology, places it in the DNA-level category, and uses adoption + efficiency data to justify its dominance — without claiming it is the only "current genetic technology that induces genetic change". [1 — explicit judgement that "DNA editing" must be sub-classified]
Finally, the lesson's three-category structure remains correct: CRISPR's success does not eliminate reproductive technologies or cloning. Each category addresses a different question — gamete combination, DNA copying, DNA insertion, or genotype preservation — and a balanced HSC response uses the three together rather than presenting CRISPR as a replacement for them. [1 — links back to the lesson's full framework]
Marking criteria.
- 1 mark — Defines genetic technology and correctly places all three editing tools in the DNA-level category.
- 1 mark — Describes two specific graph features with figures (e.g. CRISPR > 4500 by 2022; ZFN flat at ~50–200; TALEN peak ~600 in 2014).
- 1 mark — Compares the three technologies on at least three criteria using lesson + table vocabulary (design time, cleavage efficiency, off-target activity, year introduced).
- 1 mark — Quotes accurate values for the three criteria (e.g. ~5 vs ~14 vs ~90 days; ~10% / ~20% / ~40–80% efficiency).
- 1 mark — Uses Casgevy / sickle-cell as a worked example, identifying the same BCL11A target and explaining mechanistically why CRISPR was approved first.
- 1 mark — Reaches an explicit judgement that "DNA editing" must be sub-classified in a Band 5–6 HSC answer.
- 1 mark — Connects the conclusion back to the lesson's three-category framework, rejecting "CRISPR replaces everything" framing.
- 1 mark — Uses precise, lesson-faithful terminology throughout (genetic technology, induce genetic change, DNA-level, target site, cleavage, guide RNA, transgenic).
Q2 — Sample Band 6 response (8 marks), annotated
Recombinant DNA technology combines genetic material from different sources and inserts it, using a vector, into a host genome; an organism carrying inserted DNA from another species is a transgenic organism. Bt cotton is a transgenic crop: a cry gene from Bacillus thuringiensis has been inserted into the cotton genome, so cotton expresses an insecticidal protein at the DNA-encoded level. [1 — defines recombinant DNA + transgenic correctly]
What is induced in Bt cotton is a change in the DNA sequence of the cotton genome — a sequence that did not exist in any cotton plant before insertion. Artificial pollination acting on the same starting cotton population could only reshuffle alleles that already exist in cotton, so it could not generate Cry protein expression no matter how many crosses were performed. This is the lesson's key distinction between "controlling gamete combination" and "directly changing DNA sequence". [1 — identifies what is induced and where it acts; 1 — explicit contrast with reproductive technology]
The adoption data supports the claim that the technology has been broadly successful. By 2019, ~95% of US, ~94% of Indian and ~95% of Chinese cotton areas were planted with Bt cotton, up from ~35%, <1% and ~51% in 2002 respectively. Pesticide-spray reductions in the order of 40–60% are reported across all three countries, particularly in the early years of adoption. [1 — three specific data points used correctly]
However, the same data show clear limitations. Pink bollworm resistance to Cry1Ac was confirmed in Indian fields by 2010, and local Helicoverpa zea resistance was reported in the USA by 2014 — meaning the induced trait can be selected against by the pest population once it is universally present. In China, mirid bug outbreaks from 2007 onwards (a secondary pest that Bt does not target) and a declining spray-reduction advantage show that introducing one new trait can shift, rather than solve, the agricultural problem. [1 — two real limitations cited from the table; 1 — biological mechanism linked to the data]
The claim ("recombinant DNA is the most important current genetic technology") is therefore partly correct but overreaches. It is correct that recombinant DNA can introduce a trait absent from a species' allele pool, which reproductive technologies cannot do alone — this is its unique strength on the "what changes" and "why used" axes of Card 2. It is incorrect that this makes it universally "most important": once Bt cotton is established, reproductive technologies (controlled crosses, seed-system management) and refuge-area strategies are essential to delay resistance evolution; without them, the inserted trait loses value as the table shows. [1 — evaluates the claim, conceding partial correctness]
The defensible judgement is that importance is purpose-dependent, exactly as the lesson frames it. Recombinant DNA is the most important technology for introducing a new trait; reproductive technologies remain most important for spreading and managing that trait across the crop; whole-organism cloning is most important for preserving an elite genotype. A strong HSC response uses the three categories together rather than naming one as "best". [1 — purpose-dependent judgement linked back to lesson framework]
Marking criteria.
- 1 mark — Defines recombinant DNA technology and transgenic organism in lesson terms (combines DNA from different sources; vector; host genome).
- 1 mark — Identifies what is induced in Bt cotton (a DNA-sequence change introducing the cry gene) and at what level.
- 1 mark — Explicitly contrasts this with what artificial pollination of the same population could / could not produce.
- 1 mark — Cites three specific data points from the table accurately (adoption %, spray reduction, resistance year).
- 1 mark — Identifies at least two real limitations shown in the data (e.g. pink-bollworm resistance, mirid bug outbreaks, declining spray advantage).
- 1 mark — Concedes the partially-correct element of the claim (recombinant DNA can introduce traits absent from the species' allele pool).
- 1 mark — Refutes "most important universally" — explains that reproductive / management strategies remain essential to the trait's effectiveness.
- 1 mark — Reaches a purpose-dependent judgement that uses all three lesson categories (reproductive, DNA-level, whole-organism cloning) together.