B13.4 Genetic Engineering

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: changing an organism’s genome with a gene from another organism: uses, method (Higher tier) and concerns. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe genetic engineering as modifying the genome of an organism by adding a gene from another organism
• Give examples: GM bacteria making insulin, GM crops, GM animals and gene therapy
• Describe the main steps of genetic engineering, including enzymes and vectors (Higher tier)
• Outline the benefits of GM crops and the concerns some people have

Key words

• Genetic engineering: Modifying the genome of an organism by introducing a gene from another organism, to give a desired characteristic. Also called genetic modification (GM).
• GM crop: A genetically modified crop plant, e.g. one that resists insect pests or a weedkiller.
• Plasmid: A small ring of DNA found in the cytoplasm of bacteria.
• Vector: Something that carries the gene into the new cell: usually a bacterial plasmid or a virus (Higher tier).
• Enzymes: In genetic engineering, enzymes are used to cut out the gene and cut open the vector, and another enzyme joins the gene in (Higher tier).
• Gene therapy: Treating an inherited disorder by putting working copies of a gene into a person's cells.

What is genetic engineering?

In genetic engineering, scientists modify the genome of an organism by introducing a gene from another organism, to give a desired characteristic. The modified organism is called a genetically modified organism (GMO). This works because a gene from one species can be read by the cells of another species.

Key fact: Selective breeding only changes how common existing alleles are, over many generations. Genetic engineering adds a new gene, often from a completely different species, in one step.

Uses of genetic engineering

• Insulin from bacteria; What is done human insulin gene put into bacteria, which are grown in large fermenters; Benefit large amounts of human insulin for people with diabetes; no need to use animal pancreases
• Pest-resistant crops; What is done gene for a protein that kills insect pests put into maize or cotton; Benefit higher yields, fewer insecticide sprays
• Herbicide- resistant crops; What is done gene for resistance to a weedkiller put into soya; Benefit farmers can spray weeds without killing the crop
• Drought- tolerant or more nutritious crops; What is done genes for drought tolerance, or for a substance the body turns into vitamin A (golden rice); Benefit food in dry areas; less blindness caused by lack of vitamin A
• GM animals; What is done human gene put into sheep, which make a blood-clotting protein in their milk; Benefit medicines for people with haemophilia
• Gene therapy (research); What is done working copy of a gene put into the cells of a person with an inherited disorder; Benefit could treat disorders such as cystic fibrosis

How it is done (Higher tier)

• 1. Enzymes are used to cut out (isolate) the required gene from the DNA.
• 2. The same enzyme cuts open a vector: usually a bacterial plasmid, or a virus.
• 3. Another enzyme joins the gene into the vector.
• 4. The vector is used to insert the gene into the required cells. Bacteria that take it up multiply quickly, and every one makes the protein.
• In plants and animals, genes are transferred at an early stage of development (e.g. a fertilised egg or embryo), so that the organism develops with the desired characteristic in every cell.

Worked example: growth in a fermenter

A fermenter starts with 3 000 GM bacteria. They divide every 20 minutes. How many are there after 4 hours if none die?
4 hours = 240 minutes = 240 ÷ 20 = 12 divisions. 3 000 × 2¹² = 3 000 × 4 096 = 12 288 000
In standard form: 1.2288 × 10⁷ ≈ 1.2 × 10⁷

Answer: about 1.2 × 10⁷ bacteria

Benefits and concerns about GM crops

GM crops can give higher yields, need fewer pesticide sprays and may grow in difficult conditions, helping to feed a growing population. But some people are concerned:

• GM crops might affect populations of wild flowers and insects.
• Genes could spread to wild plants by pollen, e.g. producing weeds that are resistant to weedkiller.
• Some people feel the effects of eating GM crops on human health have not been fully explored.
• Some people object for moral or religious reasons to moving genes between species.

Exam tip: "Not fully explored" means there is not yet enough long-term evidence. It does not mean GM food has been shown to be harmful.

Next: You will weigh up these arguments in B13.5 Ethics of Genetic Technologies.

Common mistakes

• Mixing up genetic engineering (adding a new gene) and selective breeding (choosing parents).
• Saying the enzyme that cuts the gene out also joins it in. A different enzyme joins the gene into the vector.
• Saying a plasmid is in the nucleus of a bacterium. Bacteria have no nucleus: plasmids are in the cytoplasm.
• Forgetting why genes go into embryos: so that every cell of the organism gets the gene.

Revision questions

Try these, then check your answers below each one.

Question 1. What is genetic engineering? (Choose from: Modifying the genome of an organism by introducing a gene from another organism, Choosing parents with useful characteristics and breeding them, Making genetically identical copies of an organism, Removing all the genes from a cell.)

Answer: Modifying the genome of an organism by introducing a gene from another organism

Working: Genetic engineering modifies an organism's genome by introducing a gene from another organism to give a desired characteristic.

Question 2. (Higher tier) The diagram shows the steps used to make bacteria that produce a human protein. At which step has the human gene been joined into the ring of DNA? (Choose from: 3, 1, 2, 4.)

Answer: 3

Working: At step 3 the ring of DNA (the plasmid) contains the pink human gene: an enzyme has joined it in. At step 4 the plasmid is inside a bacterium.

Question 3. True or false? Genes are transferred to plant or animal cells at an early stage of development so that the organism develops with the desired characteristic.

Answer: True

Working: The cell divides by mitosis to form all the other cells, so every cell gets the new gene.

Related lessons

• Previous lesson: B13.3 Selective Breeding
• Next lesson: B13.5 Ethics of Genetic Technologies
• In this chapter: B13.1 Variation
• In this chapter: B13.2 Evolution by Natural Selection

Continue in the full course

This lesson is section B13.4 (AGCSC1304) of our free GCSE Combined Science course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Combined Science course.