B34: Genetic Engineering
Genetic engineering, GMOs, GM crops and gene therapy
Key Definitions
Genetic engineering (genetic modification): The process of modifying the genome of an organism by introducing a gene from another organism to give it a desired characteristic. The organism produced is called a genetically modified organism (GMO).
Restriction enzyme: An enzyme that cuts DNA at a specific recognition sequence. Used to cut out the desired gene from donor DNA and cut open the vector DNA.
Ligase enzyme: An enzyme that joins pieces of DNA together. Used to join the desired gene into the vector (plasmid) DNA, forming recombinant DNA.
Vector: A carrier used to insert a gene into a host cell. Common vectors include bacterial plasmids (small circular DNA) and modified viruses.
The Process of Genetic Engineering
1. Restriction enzymes cut out the desired gene from donor DNA
2. The same restriction enzyme cuts open the vector (plasmid)
3. Ligase enzymes join the gene into the plasmid (recombinant DNA)
4. The vector is inserted into the host cell
5. The host cell produces the desired protein
2. The same restriction enzyme cuts open the vector (plasmid)
3. Ligase enzymes join the gene into the plasmid (recombinant DNA)
4. The vector is inserted into the host cell
5. The host cell produces the desired protein
| Step | Enzyme/Method | What Happens |
|---|---|---|
| 1. Cut out gene | Restriction enzyme | Cuts the desired gene from the donor organism’s DNA at specific recognition sites |
| 2. Cut open vector | Same restriction enzyme | Cuts the plasmid DNA, creating complementary sticky ends |
| 3. Join gene to vector | Ligase enzyme | Joins the gene into the plasmid DNA — forming recombinant DNA |
| 4. Insert vector | Heat shock / electroporation | The recombinant plasmid is inserted into a bacterial host cell |
| 5. Produce protein | Host cell machinery | The bacterium reads the gene and produces the desired protein |
Using the same restriction enzyme on both the gene and the plasmid creates complementary “sticky ends” — the cut ends of the gene and plasmid have matching base sequences, so they can base-pair and be joined by ligase.
Worked Examples
Example 1: Insulin Production in Bacteria
Before genetic engineering, insulin for diabetics was extracted from the pancreases of pigs and cattle — slow, expensive, and sometimes causing allergic reactions.
Process:
- The human insulin gene is cut from human DNA using a restriction enzyme
- A bacterial plasmid is cut open using the same restriction enzyme
- Ligase joins the human insulin gene into the plasmid
- The recombinant plasmid is inserted into a bacterium
- The bacterium multiplies and produces human insulin
Advantages: Large quantities of pure human insulin can be produced quickly and cheaply. No risk of allergic reactions.
Example 2: Golden Rice
Golden rice has been genetically modified to produce beta-carotene (which the body converts to vitamin A). The genes for beta-carotene production were taken from daffodils and a soil bacterium and inserted into rice.
Purpose: To reduce vitamin A deficiency in regions where rice is a staple food. Vitamin A deficiency causes blindness and weakened immunity.
Example 3: Herbicide-Resistant Crops
Crops can be engineered with a gene that makes them resistant to a specific herbicide. Farmers can spray the herbicide to kill weeds without damaging the crop.
Advantage: Higher crop yields because competition from weeds is reduced. Less cultivation needed, reducing soil erosion.
Concern: The herbicide-resistance gene could spread to wild plants, creating “superweeds”.
Example 4: Gene Therapy
Gene therapy involves inserting a healthy copy of a gene into a person’s cells to replace a faulty gene that causes a genetic disorder.
For example, in cystic fibrosis, a healthy CFTR gene could be inserted into lung cells using a vector (often a modified virus). The cells would then produce the correct protein and reduce symptoms.
Current limitations: Gene therapy is still experimental. It is difficult to get the gene into enough cells, and the effects may be temporary. There are also risks, such as the immune system reacting to the vector.
Advantages and Disadvantages of Genetic Engineering
| Advantages | Disadvantages |
|---|---|
| Increased crop yields — helps feed growing population | Unknown long-term health effects of eating GM foods |
| Improved nutritional value (e.g. golden rice with vitamin A) | Reduced biodiversity — GM crops may outcompete wild species |
| Pest and disease resistance — less need for chemical pesticides | Genes could transfer to wild plants (e.g. herbicide resistance creating superweeds) |
| Production of medicines (e.g. human insulin from bacteria) | Ethical concerns — some argue it is “playing God” or unnatural |
| Crops can grow in poor conditions (drought, salty soil) | GM seeds are expensive — farmers in developing countries may not afford them |
| Reduced use of pesticides benefits the environment | Dependence on GM seed companies — loss of farmer independence |
Comparison: Genetic Engineering vs Selective Breeding
| Feature | Genetic Engineering | Selective Breeding |
|---|---|---|
| How it works | Genes are directly inserted from another species | Parents with desired traits are bred over generations |
| Speed | Fast — results in one generation | Slow — takes many generations |
| Source of genes | Can come from any species (even different kingdoms) | Only from within the same species or closely related species |
| Precision | Very precise — specific genes are transferred | Less precise — whole genomes are mixed |
| Ethical concerns | More controversial (crossing species boundaries) | Less controversial but still has welfare issues |
Practice Questions
Q1: Foundation Name the two enzymes used in genetic engineering and state the role of each.
Q2: Foundation Describe how human insulin is produced by genetically engineered bacteria. Write the steps in order.
Q3: Foundation Give one advantage and one disadvantage of GM crops.
Q4: Higher Explain why the same restriction enzyme must be used to cut both the gene and the plasmid.
Q5: Higher Discuss the arguments for and against the use of golden rice in developing countries.
Answers
- Restriction enzyme: cuts DNA at specific sequences — used to cut out the desired gene from donor DNA and cut open the plasmid vector. Ligase enzyme: joins pieces of DNA together — used to join the desired gene into the plasmid DNA.
- 1. The human insulin gene is cut from human DNA using a restriction enzyme. 2. A bacterial plasmid is cut open using the same restriction enzyme (creating complementary sticky ends). 3. Ligase enzyme joins the human insulin gene into the plasmid, forming recombinant DNA. 4. The recombinant plasmid is inserted into a bacterium. 5. The bacterium divides and produces human insulin, which is harvested and purified.
- Advantage: Increased crop yield (or improved nutritional value, pest resistance, growing in poor conditions). Disadvantage: Unknown long-term health effects (or reduced biodiversity, gene transfer to wild plants, ethical concerns, expensive seeds).
- The same restriction enzyme must be used because it cuts DNA at a specific recognition sequence. Using the same enzyme on both the gene and the plasmid creates complementary sticky ends — the cut ends of the gene and plasmid have matching base sequences, so they can base-pair and be joined together by ligase. If different enzymes were used, the sticky ends would not be complementary and the DNA pieces could not join.
- For: Golden rice produces beta-carotene, which the body converts to vitamin A, reducing vitamin A deficiency that causes blindness and weakened immunity. Rice is a staple food in many developing countries, so golden rice could reach many people. It is a sustainable solution that does not require changes to farming practices. Against: The long-term health effects of eating GM rice are unknown. People may not want to eat GM food due to cultural or ethical concerns. The technology is controlled by large companies, potentially creating dependency. Growing only GM rice could reduce genetic diversity of rice varieties, making crops more vulnerable to disease.
Exam Tips
- Know the process of genetic engineering in the correct order: restriction enzyme cuts gene → same enzyme cuts plasmid → ligase joins → vector inserted → host produces protein. Don’t confuse restriction enzymes and ligase!
- When evaluating GM crops, always give both sides — advantages AND disadvantages. The exam often asks you to discuss both
- Don’t confuse genetic engineering with selective breeding. Genetic engineering directly changes DNA by inserting genes from another species; selective breeding uses existing variation and breeding over generations
- For gene therapy questions, mention that it is still experimental and has limitations (difficulty getting genes into cells, temporary effects, immune reaction risks)
🔢 Maths Skills
Mathematical Skills
Interpreting data on GM crop yields: calculate percentage increase using the formula (new − original) / original × 100. For example, if a GM crop yields 8.2 tonnes/ha and a non-GM crop yields 6.5 tonnes/ha, the percentage increase = (8.2 − 6.5) / 6.5 × 100 = 26.2%.
⚠️ Common Misconceptions
Watch Out!
Students often think GM food is always dangerous to eat. Wrong: GM food is always dangerous Correct: There is no evidence that eating GM food is harmful — concerns are about environmental effects and ethics, not food safety
Students often think genetic engineering is the same as selective breeding. Wrong: Genetic engineering = selective breeding Correct: GE transfers genes between different species; selective breeding uses existing variation within the same species over many generations
✍️ 6-Mark Question
Extended Answer
6 marks: Evaluate the advantages and disadvantages of GM crops.
Advantages: GM crops can have increased yields to help feed a growing population; they can be engineered for improved nutritional value (e.g. golden rice with beta-carotene reduces vitamin A deficiency); pest-resistant varieties reduce the need for chemical pesticides, benefiting the environment; crops can grow in poor conditions (drought, salty soil) improving food security. Disadvantages: the long-term health effects of eating GM food are unknown; genes could transfer to wild plants creating superweeds; GM may reduce biodiversity by outcompeting wild species; GM seeds are expensive and create dependency on large companies; some people have ethical or religious objections. Overall, GM crops offer significant benefits but must be carefully regulated to manage risks.
Mark scheme: Up to 3 marks for advantages explained, up to 3 marks for disadvantages explained, must be balanced for full marks
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
The table shows mean crop yields (tonnes/ha) for GM and non-GM maize over 3 years: Year 1: GM 8.5, non-GM 6.2; Year 2: GM 8.1, non-GM 5.8; Year 3: GM 7.9, non-GM 6.0. Calculate the percentage yield increase for each year. Why might the GM yield be decreasing over time? What other data would you need before recommending GM maize to farmers?
📝 Exam Questions by Topic
🎬 Video Resources
Ready to ace your GCSE Biology exams?
Get the best revision books and guides to boost your grades.