OxfordAQA International GCSE Biology: Genetic manipulation: cloning, genetic engineering and GM crops (9201)

This guide covers 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. The qualification is untiered. It teaches the cloning techniques, the steps of genetic engineering, GM crops and the judgements the specification expects you to make. For condensed notes use the revision notes, and for questions use the practice set. Course pages: the OxfordAQA IGCSE Biology hub and the printable checklist. To find weak spots first, try the free diagnostics.

What you need to be able to do

Section	What you must be able to do
3.5.5 a	Describe tissue culture, cuttings, embryo transplants and adult cell cloning
3.5.5 b	Describe the steps of genetic engineering: enzymes, vector, insertion into cells
3.5.5 c	Explain that genes can be transferred at an early stage of development
3.5.5 d	Define GM crops and give examples (insect resistance, herbicide resistance)
3.5.5 e	State that GM crops generally show increased yields
3.5.5 f	Describe concerns about GM crops
Whole unit	Interpret information about cloning and genetic engineering and make informed judgements

Clones and why they are identical

A clone is an organism that is genetically identical to its parent. Clones arise naturally, for example identical twins. The techniques below make clones deliberately. The common point is that none of them involves fertilisation, so there is no mixing of genes from two parents. The offspring have the same genes as the original, apart from any new mutation.

3.5.5 a: Modern cloning techniques

Tissue culture (plants)

Small groups of cells are taken from part of a plant. They are grown on a sterile nutrient medium containing the substances they need, including plant hormones. Each small group develops into a new plant.

• Thousands of identical plants can be produced from one parent, quickly and in a small space.
• Every plant has the same genes as the parent, so a valuable feature such as high yield or flower colour is kept.
• Sterile conditions matter. Bacteria and fungi grow faster on a nutrient medium than the plant cells do and would take over.

Cuttings (an older, simple method)

Gardeners cut a piece of stem from a parent plant. The cut end is placed in compost or water, often with rooting powder, and roots grow. The result is many identical new plants from one parent. No special equipment is needed, which is why it is called an older but simple method. It produces fewer plants than tissue culture.

Embryo transplants (animals)

1. Egg cells from a female with desirable features are fertilised with sperm from a male with desirable features, giving an early embryo.
2. The cells of the developing embryo are split apart before they become specialised. At this stage every cell can still develop into a whole animal.
3. Each separated group of cells grows into an embryo.
4. The identical embryos are transplanted into host mothers, where they develop.

The calves born are identical to each other. They are not identical to the host mothers, who only carry them.

Adult cell cloning

1. The nucleus is removed from an unfertilised egg cell.
2. The nucleus from an adult body cell, for example a skin cell, is inserted into the egg cell.
3. An electric shock acts as the catalyst for the egg cell to begin to divide to form embryo cells.
4. The embryo cells carry the same genetic information as that skin cell.
5. Once the embryo is a ball of cells, it is placed in the womb of an adult female, where development continues.

The animal born has the genes of the adult that supplied the body cell. It does not share nuclear genes with the egg donor or the womb mother. This is the main difference from embryo transplants: the parent is an adult whose features are already known.

Worked example 1: comparing the techniques

Tissue culture starts with 1 small group of cells. Each cycle, every group is divided into 4 pieces and each piece grows into a new group.

• After 1 cycle: 4 groups.
• After 2 cycles: 4 × 4 = 16.
• After 3 cycles: 64.
• After 4 cycles: 4⁴ = 256 groups.

Now compare cuttings. A gardener takes 12 cuttings and 9 grow roots. Percentage that rooted = 9 ÷ 12 × 100 = 75%.

The cutting method gave at most 12 new plants from one parent, while four cycles of tissue culture gave 256 from one small group. Cuttings are cheaper and need no sterile laboratory.

Worked example 2: success rates in adult cell cloning

A research team inserts adult nuclei into 240 egg cells. 30 develop into embryos, 9 pregnancies start and 3 animals are born alive.

• Percentage reaching the embryo stage = 30 ÷ 240 × 100 = 12.5%.
• Percentage of pregnancies that ended in a live birth = 3 ÷ 9 × 100 = 33% (33.3%).
• Percentage of egg cells that gave a live animal = 3 ÷ 240 × 100 = 1.25%.
• Egg cells used per live animal = 240 ÷ 3 = 80.

Most attempts fail, so the technique is costly. This matters when you are asked to judge whether cloning is worthwhile.

3.5.5 b: Genetic engineering

In genetic engineering, genes from the chromosomes of humans and other organisms can be “cut out” and transferred to cells of other organisms. The organism receiving the gene then makes the protein that the gene codes for.

The steps:

1. Isolate the gene. Enzymes are used to isolate the required gene from the chromosome of the donor. (These enzymes cut DNA at particular places.)
2. Put the gene into a vector. A vector carries the gene into another cell. It is most often a bacterial plasmid (a small ring of DNA) or a virus. The vector is cut open with enzymes and the gene is joined in. A different type of enzyme joins the DNA together.
3. Use the vector to insert the gene into the required cells. The plasmid or virus takes the gene into the cells of the new organism, for example bacteria.

Because the genetic code is shared by living things, a human gene works inside a bacterium and the bacterium makes the human protein. A single bacterium that has taken up the gene divides again and again. If one divides every 30 minutes, after 6 hours there are 2¹² = 4096 cells, each carrying the gene.

Worked example 3: not every cell takes up the gene

A scientist mixes 5000 bacteria with plasmids carrying a human gene. 40 bacteria take up a plasmid.

Percentage that took up the gene = 40 ÷ 5000 × 100 = 0.8%.

So 4960 bacteria did not. Methods that allow the successful ones to be found and grown on are essential, but you do not need the detail for this specification.

3.5.5 c: Transfer at an early stage of development

Genes can also be moved into the cells of animals, plants or microorganisms at an early stage in their development. The organism then grows with the new gene in every cell, so it has the desired characteristics as it develops. If the gene were added to an adult, only the cells reached would change. Early-stage transfer means each cell formed by division carries the gene.

3.5.5 d and e: GM crops and yields

Crops that have had their genes modified in this way are genetically modified (GM) crops. Examples:

• Insect resistant: a gene that makes the plant produce a substance harmful to certain insect pests. Less damage means more of the crop survives, and farmers may spray insecticide less often.
• Herbicide resistant: the crop tolerates a particular weedkiller. Weeds in the field die when it is sprayed, but the crop does not, so the crop faces less competition for light, water and minerals.

GM crops generally show increased yields, because pests and weeds cause less loss.

Worked example 4: interpreting a field trial

Five plots of a GM maize and five of a non-GM maize were grown on similar soil. Yields in tonnes per hectare:

Plot	1	2	3	4	5
GM	9.4	9.8	9.5	9.7	9.6
Non-GM	7.8	8.2	8.1	7.9	8.0

• Mean GM = (9.4 + 9.8 + 9.5 + 9.7 + 9.6) ÷ 5 = 48.0 ÷ 5 = 9.6 t/ha.
• Mean non-GM = 40.0 ÷ 5 = 8.0 t/ha.
• Difference = 1.6 t/ha, so the percentage increase = 1.6 ÷ 8.0 × 100 = 20%.
• The range is 0.4 t/ha in each group, and the highest non-GM plot (8.2) is below the lowest GM plot (9.4). That gives more confidence that the difference is real.
• Over 40 hectares the extra crop is 1.6 × 40 = 64 tonnes.

The data come from one site and one season, so they cannot show that GM maize will give 20% more everywhere.

3.5.5 f: Concerns about GM crops

• Wild flowers: a herbicide-resistant crop allows heavy weedkiller use, so fewer wild flowers survive.
• Insects: fewer weeds and fewer pests mean less food and fewer habitats for insects, and insect-resistant crops may harm insects that are not pests. Fewer insects affects the animals that feed on them.
• Human health: there is uncertainty about the effects of eating GM crops on human health.

Making informed judgements

You may be given a passage, table or graph about cloning or genetic engineering. Use this approach.

1. State what the information shows, with figures.
2. Give a benefit and a risk or limitation, each linked to the information.
3. Say what other evidence you would want, such as more sites, more years or independent testing.
4. Give a conclusion that follows from your points.

Worked example 5: should a farm grow the GM crop?

A trial found that a GM crop needed 2 insecticide sprays per season, against 6 for the non-GM crop.

• Reduction = (6 − 2) ÷ 6 × 100 = 67%.
• On a farm of 25 hectares, one spray per hectare each time, the total falls from 6 × 25 = 150 to 2 × 25 = 50 sprays: 100 fewer.
• Benefit: lower costs and fewer chemicals in the environment.
• Concern: the trial does not show effects on wild insects or wild flowers near the field, or on health.
• Judgement: the evidence supports a benefit to the farmer, but a decision would need information on wider effects.

For cloning, the same style works. A cloned herd keeps the best features, but identical animals mean no genetic variation, so one disease could affect all of them, and the success rate may be low.

Common errors

• Saying cuttings and tissue culture involve seeds or fertilisation. They do not.
• Saying the clone is identical to the host mother or egg donor. In adult cell cloning it matches the adult that gave the body cell.
• Forgetting that embryo cells must be split before they become specialised.
• Calling the vector the gene. The vector carries the gene.
• Saying plasmids are in the human cell. The plasmid is a bacterial vector.
• Writing that GM crops are “proven unsafe” or “proven safe”. The specification says there is uncertainty.
• Giving an opinion with no evidence from the information supplied.

Official syllabus

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