Manipulation of food species to increase productivity: the advantages and disadvantages of the methods that are available to improve crop and livestock gene pools — AQA A-Level Environmental Science

Manipulation of food species gene pools covers the scientific principles, applications, and environmental impacts of artificial selection, asexual cloning, induced polyploidy, and genetic modification. These interventions aim to enhance desirable agronomic characteristics including yield, pest resistance, nutritional value, and tolerance to abiotic stressors such as salinity and drought.

Understanding these techniques is vital in Environmental Science as humanity faces the dual challenge of feeding an expanding global population while mitigating agrochemical runoff, habitat loss, and climate instability. Evaluating the trade-offs between agricultural productivity, biodiversity loss, and genetic erosion is central to sustainable food production systems.

• →Selective breeding (artificial selection) increases target allele frequencies over successive generations but risks inbreeding depression and genetic bottlenecking.
• →Genetic modification (transgenics/cisgenics) transfers specific genes across species boundaries to introduce novel traits like Bt endotoxin production or herbicide resistance.
• →Asexual propagation and somatic cloning reproduce identical, elite genotypes, eliminating genetic variation across commercial populations.
• →Induced polyploidy (e.g. using colchicine) creates organisms with multiple chromosome sets, commonly leading to larger plant organs and seedless fruit (e.g. triploid crops).
• →Genetic erosion occurs when high-yielding monocultures displace traditional landraces, reducing the reservoir of wild alleles available for future crop breeding.

• Defines an energy ratio as usable food energy output divided by energy input, applied consistently to both systems
• Contrasts high input use in intensive systems with lower input reliance in extensive systems
• Explains that intensive systems raise yield per hectare while often lowering the energy ratio
• Explains that extensive systems give lower yield per hectare but frequently a higher energy ratio
• Accounts for embodied energy in fertiliser, machinery, pesticides and feed when comparing systems
• States the system boundary and keeps the comparison like-for-like
• Concludes that productivity and energy efficiency can diverge, producing a trade-off

• 💡State the ratio definition and the system boundary before comparing the two systems
• 💡Use a worked example with consistent units to show how the ratio is calculated
• 💡Structure the answer around inputs, outputs and the resulting ratio for each system
• 💡Finish with an explicit judgement about the trade-off between yield and efficiency
• 💡When evaluating GM crops, always balance environmental benefits (e.g. reduced insecticide spraying) against environmental risks (e.g. horizontal gene transfer to wild relatives creating superweeds).
• 💡Distinguish clearly between gene pools (the total diversity of genes/alleles in a breeding population) and genotypes (the specific genetic makeup of an individual).
• 💡Mention the importance of wild crop relatives and seed banks (e.g. Svalbard) as essential repositories of genetic diversity when discussing solutions to genetic erosion.

• Compares yield per hectare alone; include the energy invested to obtain that yield
• Counts only direct fuel use; include embodied energy in fertilisers, pesticides and feed
• Changes the system boundary between the two systems; apply the same boundary to both
• Assumes the more productive system is always the more efficient; separate yield from energy ratio
• Believing that selective breeding cannot alter chromosome number: Induced polyploidy is a specific method used in plant breeding to double chromosome sets, distinct from standard cross-pollination.
• Assuming all genetically modified organisms contain animal genes: Most commercial GM crops involve bacterial genes (such as Bacillus thuringiensis) or altered plant genes (cisgenics).
• Assuming hybrid seeds can be saved and replanted with identical yields: F1 hybrids segregate in the F2 generation due to meiosis, causing loss of hybrid vigour and variable phenotypes.

1. 1Day 1-3: Review and create a comparison table contrasting selective breeding, cloning, polyploidy, and genetic engineering by mechanism, speed, and application.
2. 2Day 4-6: Analyse case studies: Bt cotton, Golden Rice, F1 hybrid maize, and Belgian Blue cattle, focusing on environmental pros and cons.
3. 3Day 7-9: Practice 6-mark and 9-mark evaluation questions focusing on gene pool depletion and food security.
4. 4Day 10-12: Test recall using flashcards on key terminology (heterosis, inbreeding depression, transgenics, landraces).

• 📋Comparative evaluate questions (6-9 marks) asking you to weigh up the environmental and ethical impacts of GM vs selective breeding.
• 📋Data analysis questions requiring interpretation of crop yield changes, pesticide usage trends, or pest resistance rates over time.
• 📋Short explanation questions (2-4 marks) focusing on biological mechanisms like hybrid vigour, inbreeding depression, or polyploidy.