OxfordAQA International GCSE Biology: Genetic manipulation: cloning and GM crops (9201) – Revision Notes

These notes condense section 3.5.5 (Genetic manipulation, parts a to f) of the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams May/June 2018 onwards. Use the study guide for fuller explanations and worked examples. Then test yourself with the practice questions. Course pages: the OxfordAQA IGCSE Biology hub and the printable checklist. Not sure what to revise first? Take a free diagnostic.

3.5.5 a: Cloning techniques at a glance

A clone is genetically identical to its parent. No fertilisation, so no mixing of genes.

Technique	Organism	Starting material	Key points
Tissue culture	Plants	Small groups of cells from part of a plant	Sterile nutrient medium; many identical plants quickly
Cuttings	Plants	Piece of stem from parent	Older, simple method used by gardeners; roots grow from the cut end
Embryo transplants	Animals	Cells of a young embryo	Split apart before they become specialised; identical embryos go into host mothers
Adult cell cloning	Animals	Egg cell plus nucleus of an adult body cell	Offspring matches the adult body-cell donor

Adult cell cloning in steps

1. Remove the nucleus from an unfertilised egg cell.
2. Insert the nucleus from an adult body cell, for example a skin cell.
3. An electric shock acts as the catalyst for the egg cell to begin dividing into embryo cells.
4. These cells carry the genetic information of the skin cell.
5. At the ball-of-cells stage, place the embryo in the womb of an adult female.

Embryo transplants in steps

1. Obtain an early embryo.
2. Split the cells apart before they become specialised.
3. Let each group grow into an embryo.
4. Transplant the identical embryos into host mothers.

Must-know distinctions

• Embryo transplant vs adult cell cloning: in an embryo transplant the offspring are identical to each other, but the parents were chosen before the animal’s features were known. In adult cell cloning the offspring match an adult whose features are known.
• Cuttings vs tissue culture: cuttings need no equipment and give few plants. Tissue culture needs sterile conditions and gives very many.
• Donor vs host: the host mother carries the embryo. She is not the genetic parent of an embryo-transplant or adult-cell clone.

Benefits and limits to quote in judgements

Technique	Possible benefit	Possible limit
Tissue culture	Many identical plants from a small amount of tissue, kept all year	Needs sterile conditions and trained staff; all plants share the same weaknesses
Cuttings	Cheap and simple; copies a plant with known features	Slow and limited number of new plants
Embryo transplants	Several offspring from a valued female and male	Offspring are identical to each other, so there is no variation within the group
Adult cell cloning	Copies an adult animal whose features are already proven	Many attempts fail; costly; ethical objections
Genetic engineering	Can give an organism a feature it could not gain by breeding	Uncertainty about long-term effects; public concern
GM crops	Higher yield; fewer sprays for an insect-resistant crop	Possible effects on wild flowers and insects; uncertainty about human health

Why identical organisms can be a risk

Clones have the same genes, so they have the same weaknesses. If one individual is killed by a disease, all of them may be. Natural populations that reproduce sexually have variation, so some individuals are likely to survive.

3.5.5 b and c: Genetic engineering

Genes from the chromosomes of humans and other organisms can be “cut out” and transferred to cells of other organisms.

Step	What happens
1	Enzymes isolate the required gene
2	The gene is put into a vector (a bacterial plasmid or a virus is usual)
3	The vector inserts the gene into the required cells

• A plasmid is a small ring of DNA found in bacteria.
• The cells then make the protein coded by the new gene.
• Early-stage transfer: a gene put into an animal, plant or microorganism early in its development ends up in all its cells, so it grows with the desired features.

Worked reminder: percentage and doubling

• 36 embryos transplanted, 24 calves born: 24 ÷ 36 × 100 = 66.7% success.
• A bacterium dividing every 30 minutes for 6 hours: 12 divisions, 2¹² = 4096 cells.
• 40 of 5000 bacteria take up a gene: 40 ÷ 5000 × 100 = 0.8%.

3.5.5 d, e and f: GM crops

Point	Detail
Definition	Crops that have had their genes modified by genetic engineering
Examples	Insect resistant; herbicide resistant
Yield	GM crops generally show increased yields
Concerns	Effect on populations of wild flowers and insects; uncertainty about the effects of eating GM crops on human health

Why yields rise

• Insect resistance: less pest damage, fewer sprays.
• Herbicide resistance: weeds are killed but the crop survives, so less competition.

Method in steps: judging cloning or GM information

1. Quote figures from the data.
2. Give one benefit and one limit, each tied to the information.
3. Say what extra evidence is needed.
4. Give a conclusion that follows.

Worked reminder: percentage increase in yield

Mean yield rises from 7.5 to 8.4 tonnes per hectare. Change = 0.9. Percentage increase = 0.9 ÷ 7.5 × 100 = 12%.

Worked reminder: reading a trial

A trial grows an insect-resistant crop and a non-GM crop in 4 plots each. GM yields (tonnes per hectare): 6.1, 6.3, 6.0, 6.2. Non-GM yields: 5.4, 5.6, 5.5, 5.5.

• Mean GM = 24.6 ÷ 4 = 6.15.
• Mean non-GM = 22.0 ÷ 4 = 5.5.
• Difference = 0.65, which is 0.65 ÷ 5.5 × 100 = 11.8% (about 12%).
• Every GM plot is above every non-GM plot, but the trial is only 8 plots, so more sites and years would be needed.

Concerns in more detail

• Wild flowers: if fields are sprayed with weedkiller more freely, wild flowers that grow among crops die, and the animals that depend on them lose food.
• Insects: insects that feed on the weeds, or on the crop, may decline. Other animals that eat those insects lose a food supply.
• Human health: nobody can yet say with certainty what the effects of eating GM crops are. Say “uncertain”, not “harmful”.

Key terms

• Clone: an organism genetically identical to its parent.
• Specialised cell: a cell that has become adapted to one job and can no longer develop into any cell type.
• Vector: the carrier, usually a bacterial plasmid or a virus, that moves a gene into a cell.
• Plasmid: a small ring of DNA in bacteria.
• Genetic engineering: cutting out a gene and transferring it to the cells of another organism.
• GM crop: a crop whose genes have been modified by genetic engineering.
• Host mother: the female in whose womb a transplanted embryo develops.
• Herbicide: a chemical that kills weeds.

Quick self-test

1. Name two plant cloning methods.
2. Why must embryo cells be split early?
3. What is removed from the egg cell in adult cell cloning?
4. What acts as the catalyst for the egg cell to begin dividing?
5. Where is the embryo placed at the end of adult cell cloning?
6. What do enzymes do in the first step of genetic engineering?
7. Name two types of vector.
8. Why does early-stage gene transfer mean every cell carries the gene?
9. Give one example of a GM crop trait.
10. State one concern about GM crops and wild populations.
11. 9 of 12 cuttings root. Calculate the percentage.
12. A crop yield rises from 8.0 to 9.6 tonnes per hectare. Calculate the percentage increase.

Answers

1. Tissue culture and cuttings.
2. After they become specialised, the cells can no longer develop into a whole animal.
3. The nucleus.
4. An electric shock.
5. In the womb of an adult female.
6. They isolate the required gene.
7. A bacterial plasmid and a virus.
8. The gene is present before the cells divide, so each new cell copies it.
9. Resistance to insect attack, or resistance to herbicides.
10. Effects on populations of wild flowers and insects.
11. 9 ÷ 12 × 100 = 75%.
12. (9.6 − 8.0) ÷ 8.0 × 100 = 20%.

Where marks are usually lost

• Describing a clone as having “similar” genes. Clones are genetically identical.
• Forgetting the nucleus is removed from the egg cell, so the egg does not contribute its own nuclear genes.
• Writing that the electric shock fertilises the egg.
• Saying the plasmid is cut out of the human cell. The gene comes from the donor and the plasmid is the vector.
• Missing the word “specialised” when explaining embryo splitting.
• Giving a concern with no link to the information supplied, such as “it is unnatural”.
• Using the final value as the denominator in a percentage change.
• Giving only one side in a “make a judgement” question.

Official syllabus

OxfordAQA International GCSE Biology (9201), Version 5.2, for exams May/June 2018 onwards, published by OxfordAQA. These notes cover section 3.5.5 Genetic manipulation, parts a to f.