Biology • Year 12 • Module 6 • Lesson 18
Long-Term Population Change
Apply Module 6's threads, mutation, selection, drift, biotechnology and context, to scenarios that decide whether a population actually changes over generations.
1. Graph, allele frequency vs time under three uptake scenarios
A research team modelled the frequency of a beneficial allele R (introduced via a Bt-style biotech crop) over 40 generations in three otherwise identical farming regions. The only difference between regions is the real-world uptake: Region A is fully adopted, Region B is partially adopted, Region C is blocked by regulation. 8 marks
Stylised model, illustrative of "capability + uptake → change" (Lesson 18) layered onto a beneficial-allele sweep (Module 6 Lessons 6–7).
1.1 Describe the trend in frequency of allele R in each region from generation 0 to 40, quoting at least one numerical value per region. 3 marks
1.2 The biotech crop has identical scientific capability in all three regions. Explain why allele R still sweeps to high frequency in A, only partially rises in B, and stays flat in C. Use the terms uptake, regulation and economic context. 3 marks
1.3 Region C is unchanged. Does Lesson 18 say the technology has "failed"? Justify in one sentence using the framework "capability versus uptake". 2 marks
2. Data table, predict the population-level impact
For each biotechnology, four context factors have been scored from 0 (severely limiting) to 3 (highly favourable). Use the table to predict which technology is most likely to produce long-term population change. 7 marks
| Biotechnology | Capability (lab) | Cost / access (econ.) | Regulation | Public & community acceptance | Total |
|---|---|---|---|---|---|
| W Bt cotton in commercial agriculture | 3 | 2 | 2 | 2 | |
| X Germ-line CRISPR in human embryos | 3 | 0 | 0 | 0 | |
| Y Gene-drive cane-toad release in northern Australia | 2 | 1 | 0 | 0 | |
| Z Somatic gene therapy for sickle-cell anaemia (US/EU patients) | 3 | 0 | 2 | 2 |
2.1 Complete the "Total" column. 2 marks
2.2 Which biotechnology is most likely to drive long-term population change in its target population, and why? Identify the limiting factor for the lowest-scoring technology. 3 marks
2.3 Technology Z has the same lab capability as X but a much higher total. Explain why, in lesson terms. 2 marks
3. Cause-and-effect ladder, module synthesis
The boxes on the left are filled with mechanisms from earlier in Module 6. Complete the empty boxes on the right with the population-level effect, then close with an "Overall outcome" line in Lesson 18 terms. 6 marks (1 per effect, 1 overall)
| Cause (from earlier M6 lessons) | So… (population-level effect, in your words) |
|---|---|
| 3.1 Random mutation introduces a new allele into the gene pool (L1, L3) | |
| 3.2 Natural selection favours individuals carrying that allele over generations (Bio Module 4 review) | |
| 3.3 Random genetic drift in a small population (L7) | |
| 3.4 A recombinant DNA / CRISPR insertion creates a new variant in one organism (L13, L16) | |
| 3.5 Widespread biotechnology uptake spreads that variant repeatedly through a population (L18) |
Overall outcome (one sentence): Lesson 18 says long-term population change happens when…
4. Predict-and-justify, a real case
AquaBounty's AquAdvantage salmon (a transgenic Atlantic salmon carrying a Chinook salmon growth-hormone gene under an ocean-pout promoter) was FDA-approved for sale in 2015. By 2024 it is sold in some US supermarkets but remains banned for sale in most EU markets and is grown only in tightly-contained land-based tanks. There are no confirmed wild-population introductions. 5 marks
4.1 Identify one social/cultural factor and one regulatory factor that have limited the impact of AquAdvantage salmon on global salmon populations. 2 marks
4.2 Predict what would happen to wild Atlantic-salmon allele frequencies if the technology were widely released into open net-pens (i.e. high uptake, weak regulation). Justify using Module 6 mechanisms. 2 marks
4.3 In one sentence, restate Lesson 18's main claim using this case as the example. 1 mark
Q1.1, Trend description (3 marks)
Region A: the frequency of R rises steeply from about 0.05 at generation 0 to roughly 0.85 at generation 40, a near-sweep [1]. Region B: R rises slowly and shallowly, from about 0.05 to roughly 0.30, never approaching fixation [1]. Region C: the frequency stays essentially flat at about 0.05 for all 40 generations [1].
Q1.2, Why uptake explains the difference (3 marks)
In every region the biotech crop has identical scientific capability, so the difference between curves is not biological, it is about uptake [1]. Region A has full economic and regulatory access, so the allele is repeatedly introduced and selected upward in most fields; Region B has only partial uptake (some farmers cannot afford the seed or refuse to adopt it), so R rises slowly because it enters only some of the population [1]. Region C's regulation prohibits release, so the allele is never introduced into the field gene pool, capability is intact but uptake is zero, so allele frequency does not change [1].
Q1.3, Has the technology "failed" in Region C? (2 marks)
No, Lesson 18 distinguishes capability from uptake [1]. In Region C the capability is unchanged; the regulation has prevented uptake, which is a context-level outcome, not a scientific failure. The technology has simply not been permitted to produce long-term population change [1].
Q2.1, Totals (2 marks)
W = 3 + 2 + 2 + 2 = 9; X = 3 + 0 + 0 + 0 = 3; Y = 2 + 1 + 0 + 0 = 3; Z = 3 + 0 + 2 + 2 = 7. 1 mark for all four correct; deduct 1 mark for any arithmetic error. Award 1 mark if at least two are correct.
Q2.2, Most likely to drive long-term change (3 marks)
W (Bt cotton) is most likely, high capability with reasonable scores across cost, regulation and acceptance, giving the widest possible uptake [1]. Of the two equal lowest scorers (X and Y), X is limited primarily by regulation and cultural rejection of germ-line human editing, and Y is limited primarily by regulation and community rejection of gene-drive releases [1]. Either is accepted as a correct identification of the limiting factor, provided the factor is named and tied to the score of 0 [1].
Q2.3, Why Z scores higher than X despite equal capability (2 marks)
Both have the same lab capability, but Z is a somatic therapy that does not edit the human germ-line, so its regulatory and cultural acceptance scores are far higher than X's [1]. Z therefore translates more of its capability into actual uptake; X has the capability but very little of it converts into real-world adoption, exactly the Lesson 18 framing [1].
Q3, Cause-and-effect ladder (6 marks)
3.1 A new allele appears at very low frequency in the gene pool, raising the genetic variation available for change [1].
3.2 The favoured allele's frequency rises over generations as carriers leave more offspring, directional change in the gene pool [1].
3.3 Allele frequencies fluctuate randomly between generations; alleles can be lost or fixed by chance, especially in small populations [1].
3.4 A novel variant exists in one organism, but it is not yet a population-level change; capability without uptake [1].
3.5 The variant is repeatedly introduced and propagated across many individuals, so its frequency rises in the population over multiple generations [1].
Overall outcome: long-term population change happens when a genetic variant (from mutation, selection, drift or biotechnology) is matched by sustained, widespread real-world uptake that is permitted by social, economic, cultural and regulatory context [1].
Q4.1, Social/cultural + regulatory limits on AquAdvantage salmon (2 marks)
Social/cultural: negative consumer perception ("Frankenfish" media framing) and labelling-led shopper rejection in many markets, public acceptance is low [1]. Regulatory: EU bans on sale, mandatory containment-only farming, and import restrictions in many countries, these are explicit regulatory limits on uptake [1].
Q4.2, Prediction under high uptake + weak regulation (2 marks)
If transgenic salmon escaped into the wild in large numbers and interbred with wild Atlantic salmon, the growth-hormone transgene could enter the wild gene pool via gene flow [1]. Selection on body size and reproductive success, combined with the sheer number of escapees, could drive the frequency of the transgenic allele upward across generations, producing genuine long-term population change in wild salmon [1].
Q4.3, One-sentence restatement (1 mark)
"AquAdvantage salmon shows that scientifically successful biotechnology produces long-term population change only when social acceptance, economic access and regulation also permit widespread uptake, capability is biologically possible but socially mediated." [1]