4.4Unit 2 · Use of Biological Resources
Cloning — Unit 2 — Edexcel IGCSE Biology Modular - UNIT 2 Revision Notes & Topical Questions
10 min read 4 parts Lesson 5 of 5 1 quiz
Lesson summary
Describe the process of micropropagation.Micropropagation uses small pieces of tissue called explants, often from shoot tips.Explants are sterilised and grown on agar containing nutrients and plant hormones.Hormones make explants form roots and shoots; plantlets are transferred t…
- Micropropagation (tissue culture)
- Cloning mammals
- Why plants clone from tissue
- Further advantages of micropropagation
- Explain why sterile conditions are essential in micropropagation
- Aseptic technique
Section 1 of 4Cloning — Unit 2
Cloning
produces genetically identical organisms. Many plants reproduce this way naturally; humans use techniques to clone plants and animals artificially.Micropropagation (tissue culture):
small pieces (explants) are cut from the shoot tips of a parent plant with desired features. They are sterilised, for example with dilute bleach, to kill microorganisms.- The explants are placed on sterile agar medium containing nutrients (glucose, mineral ions) and plant hormones. Cells divide by mitosis to form a mass of cells, then hormones stimulate growth of shoots and roots.
- The small plantlets are moved into compost in a greenhouse to grow.
- Thousands of identical plants can be produced quickly, all year round, in a small space.
- It is used for commercially valuable plants like orchids and for conserving rare species.
Cloning mammals:
the nucleus is removed from an egg cell and replaced with the nucleus of a body cell from the animal to be cloned. An electric shock makes the cell divide; the embryo is implanted into a surrogate mother.Uses:
producing many copies of a high-value animal (e.g. a top milk-producing cow); producing herds of genetically modified animals that make medicines in their milk; possibly saving endangered species.Problems:
low success rate, high cost, possible early ageing or health problems in clones, lack of variation making populations vulnerable to disease, and ethical objections.Callus:
In tissue culture the sterilised explant first grows into a small mass of undifferentiated cells called a callus. Moving it to a medium with different plant hormones makes it form roots, stems and leaves (a plantlet).Why plants clone from tissue:
Many plant cells keep the ability to differentiate into any cell type, so a small piece can grow into a whole plant.- In animals only embryonic stem cells can do this, so a piece of adult animal tissue cannot develop into a new individual.
Further advantages of micropropagation:
Plantlets are grown in sterile conditions, so they are disease-free, and a disease-resistant parent passes resistance to every clone. Plantlets reach maturity faster than plants grown from seed.
Section 2 of 4Process & sequence
- Take a body cell (e.g. udder cell) from the adult to be cloned; keep its nucleus.
- Take an egg cell from a second female and remove its nucleus (enucleation).
- Insert the diploid nucleus from the body cell into the enucleated egg.
- Give an electric shock to fuse the cell and stimulate it to divide by mitosis.
- Grow the embryo for a few days in the laboratory.
- Implant the embryo into the uterus of a surrogate mother.
- The offspring born is genetically identical to the nucleus donor.
Micropropagation — write these steps in this order; each step is a marking point.
- Choose parent plant
- Cut small explants
- Sterilise explants
- Grow on agar with hormones
- Shoots and roots form
- Transfer plantlets to compost
Section 3 of 4Compare
| Feature | Micropropagation | Cloning mammals |
|---|---|---|
| Starting material | Small explants from shoot tips | Nucleus of an adult body cell and an egg cell |
| Key step | Growth on sterile agar with hormones | Nuclear transfer into enucleated egg |
| Stimulus | Plant hormones (auxins, cytokinins) | Electric shock to start division |
| Success rate | High, thousands of plants | Low, many embryos fail |
| Example | Orchids, bananas, rare plants | Dolly the sheep (1996) |
| Advantages | Disadvantages |
|---|---|
| Many identical offspring with desired traits | No genetic variation – disease risk |
| Fast; independent of season (plants) | Expensive, needs skilled staff |
| Can save rare or endangered species | Low success rate and health problems in cloned animals |
| Could produce GM animals making medicines | Ethical concerns |
Section 4 of 4Worked examples
A cloned lamb was produced using a nucleus from a Finn Dorset sheep, an egg from a Scottish Blackface sheep, and a Scottish Blackface surrogate. Which sheep will the lamb resemble, and why?
- The lamb will resemble the Finn Dorset sheep because the nucleus, which contains nearly all the genetic information, came from that sheep.
- The egg donor's nucleus was removed and the surrogate only provides the environment for development.
- The lamb will resemble the Finn Dorset sheep because the nucleus, which contains nearly all the genetic information, came from that sheep.
Explain why sterile conditions are essential in micropropagation.
- The agar medium contains nutrients that bacteria and fungi could also use.
- Microorganisms would grow rapidly, compete with and infect or kill the explants, so equipment and explants are sterilised.
- The agar medium contains nutrients that bacteria and fungi could also use.
Marked practiceQuizzes for this lesson
Last updated: