14.5 Cloning

A free GCSE Biology lesson for AQA (8461) from OBA School: clones in nature, cuttings and tissue culture in plants, and embryo transplants in animals. 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

• Explain what a clone is and how clones form in nature
• Describe how to take plant cuttings
• Describe tissue culture and explain why it is useful
• Describe embryo transplants in animals and explain why the offspring are clones of each other

Key words

• Clone: An individual that is genetically identical to another.
• Asexual reproduction: Reproduction with one parent and no fusion of gametes. The offspring are clones, made by mitosis.
• Cutting: A small piece of a plant (usually a shoot) that grows roots and becomes a new plant.
• Tissue culture: Growing new plants from small groups of cells on a sterile growth medium.
• Embryo transplant: Splitting an early embryo into separate cells and placing each in a host mother.
• Host mother: A female who carries an embryo that is not genetically her own (also called a surrogate).

Clones in nature

A clone is genetically identical to its parent or to another individual. Clones are made by asexual reproduction, which uses mitosis only. Examples: strawberry plants sending out runners, bacteria dividing, and identical twins (which form when an early embryo splits naturally).

Key fact: Clones have the same genes, but they can still look different if they grow in different environments.

Taking cuttings

Taking cuttings is an older, simple method that gardeners use to produce many identical new plants from a good parent plant.

Method

1. Cut a short shoot with a few leaves from the parent plant.

2. Remove the lower leaves (less water loss).

3. Dip the cut end in rooting powder – it contains plant hormones that make roots grow.

4. Plant it in damp compost and cover with a clear plastic bag to keep the air moist.

5. In a few weeks it grows roots and becomes a new plant – a clone of the parent.

Benefits: Cuttings are cheap and quick, and each new plant has the same useful features (e.g. flower colour) as the parent.

Tissue culture

Tissue culture uses small groups of cells from part of a plant to grow identical new plants. It must be done in aseptic (sterile) conditions, because microorganisms would grow on the nutrient medium and kill the cells.

Uses: preserving rare plant species (thousands of plants from very little material) and commercial plant nurseries, which can produce huge numbers of identical plants quickly, all year round.

Worked example: how many plants?

One plant tip is cut into 25 pieces. Every 4 weeks, each cluster of plantlets can be split into 6. How many plantlets are there after 12 weeks?
12 weeks = 3 rounds of splitting. 25 × 6 × 6 × 6 = 25 × 216 = 5400

Answer: 5400 plantlets from one plant tip

Embryo transplants in animals

Farmers use embryo transplants to get many offspring from their best animals. Cells are split apart from a developing embryo before they become specialised, then the identical embryos are transplanted into host mothers.

Exam tip: The calves are clones of each other, but not of their parents: the embryo came from sexual reproduction, so it has a mix of alleles from the bull and the cow.

Common mistakes

• Saying embryo transplant calves are clones of their parents. They are clones of each other only.
• Saying the embryo is split after its cells are specialised. It must be split before, so each cell can still form a whole animal.
• Saying cuttings need sterile conditions. Tissue culture does; cuttings do not.
• Forgetting the downside of clones: no variation, so one disease could affect them all.

Revision questions

Try these, then check your answers below each one.

Question 1. Which is the older, simple method gardeners use to produce new plants identical to a parent? (Choose from: Adult cell cloning, Embryo transplants, Taking cuttings, Tissue culture.)

Answer: Taking cuttings

Working: Taking cuttings is cheap and simple. Tissue culture is the modern, sterile lab method.

Question 2. True or false? Calves produced by an embryo transplant are genetically identical to their parents.

Answer: False

Working: False. The embryo came from sexual reproduction, so the calves are identical to each other but not to their parents.

Question 3. Why must tissue culture be carried out in aseptic (sterile) conditions? (Choose from: The plant hormones would become toxic, The cells need an oxygen-free environment, Microorganisms would grow on the nutrient medium and harm the plant cells, Light would kill the plant cells.)

Answer: Microorganisms would grow on the nutrient medium and harm the plant cells

Working: Microorganisms would grow on the nutrient-rich medium, competing with and killing the plant cells.

Related lessons

• Previous lesson: 14.4 Genetic Engineering
• Next lesson: 14.6 Adult Cell Cloning
• In this chapter: 14.1 Variation
• In this chapter: 14.2 Evolution by Natural Selection
• In this chapter: 14.3 Selective Breeding

Continue in the full course

This lesson is section 14.5 (AGCBH1405) 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.