14.4 Genetic Engineering

A free GCSE Biology lesson for AQA (8461) 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 what genetic engineering is
• Give examples of genetically engineered bacteria and crops, and of gene therapy
• Describe the main steps of genetic engineering, including enzymes and vectors (Higher tier)
• Outline the benefits and concerns about GM crops

Key words

• Genome: The entire genetic material of an organism.
• Genetic engineering: Modifying the genome of an organism by adding a gene from another organism, to give a useful characteristic.
• GM crop: A genetically modified crop plant, e.g. one that resists insect pests.
• Plasmid: A small ring of DNA found in the cytoplasm of bacteria.
• Vector: Something that carries the gene into the new cell, usually a plasmid or a virus (Higher tier).
• Restriction enzyme: An enzyme that cuts DNA at a particular base sequence, leaving "sticky ends" (Higher tier).
• Ligase: An enzyme that joins pieces of DNA together (Higher tier).

What is genetic engineering?

In genetic engineering, scientists cut a gene out of one organism and put it into the genome of another, so that it gains a useful characteristic. This works because almost all organisms use the same genetic code, so a human gene can be read by a bacterium.

Key fact: Selective breeding only changes how common existing alleles are. Genetic engineering adds a new gene, often from a completely different species, in a single generation.

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 pure human insulin for people with diabetes
• Pest-resistant crops; What is done Gene for a protein that kills certain insect larvae put into crops; Benefit Higher yields, fewer insecticide sprays
• Herbicide- resistant crops; What is done Gene for resistance to a weedkiller put into crops; Benefit Farmers can kill weeds without harming the crop
• Better fruit and nutrition; What is done Genes for bigger fruit or extra vitamins, e.g. rice that makes a substance the body turns into vitamin A; Benefit Better yield or diet
• 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)

• Restriction enzymes cut the required gene out of the DNA, leaving short single-stranded "sticky ends".
• The same enzyme cuts open a vector – usually a bacterial plasmid, or a virus – giving matching sticky ends.
• Ligase enzyme joins the gene into the vector.
• The vector carries the gene into the new cells. Bacteria that take it up multiply and make the protein.
• For plants and animals, the gene is put into cells at an early stage of development (e.g. a fertilised egg or embryo), so every cell that grows from it by mitosis contains the gene.

Worked example: growth in a fermenter

A fermenter starts with 1000 GM bacteria. They divide every 30 minutes. How many are there after 6 hours if none die?
6 hours = 360 minutes = 12 divisions. 1000 × 2¹² = 1000 × 4096 = 4 096 000
In standard form: 4.096 × 10⁶ ≈ 4.1 × 10⁶

Answer: about 4.1 × 10⁶ 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 (for example, insects that feed on pests).
• Genes could spread to wild relatives by pollen, e.g. producing herbicide-resistant weeds.
• The long-term effects of eating GM crops on human health have not been fully explored.

Next: You will weigh up these arguments in 14.7 Ethics of genetic technologies.

Common mistakes

• Mixing up genetic engineering and selective breeding.
• Saying restriction enzymes join DNA. They cut it; ligase joins it.
• 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: Choosing parents with useful characteristics to breed, Making identical copies of an organism, Splitting an embryo into separate cells, Modifying an organism’s genome by adding a gene from another organism.)

Answer: Modifying an organism’s genome by adding a gene from another organism

Working: Genetic engineering adds a gene from one organism to another to give a desired characteristic. The other options are selective breeding and cloning.

Question 2. True or false? Genes are put into plant or animal cells at an early stage of development so that all the cells of the organism contain the gene.

Answer: True

Working: True. Every cell that grows from the modified cell by mitosis contains the new gene, so the organism shows the characteristic.

Question 3. Name the hormone produced by genetically engineered bacteria to treat diabetes.

Answer: insulin

Working: GM bacteria make human insulin for people with diabetes.

Related lessons

• Previous lesson: 14.3 Selective Breeding
• Next lesson: 14.5 Cloning
• In this chapter: 14.1 Variation
• In this chapter: 14.2 Evolution by Natural Selection
• In this chapter: 14.6 Adult Cell Cloning

Continue in the full course

This lesson is section 14.4 (AGCBH1404) of our free GCSE Biology 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 Biology course.