Cloning — Edexcel International GCSE Biology
Micropropagation of plants, cloning mammals such as Dolly the sheep, and how cloned transgenic animals make human proteins.
Revision notes
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Micropropagation, or tissue culture, is growing new plants from small pieces of plant tissue called explants in vitro. Sterilised explants are placed on sterile nutrient agar containing nutrients and plant growth hormones, using aseptic technique. They grow into plantlets that are genetically identical to the parent, so commercial quantities of plants with desirable characteristics are produced quickly.
Mammals such as Dolly the sheep are cloned by putting a diploid nucleus from a mature body cell into an enucleated egg cell, which has had its own nucleus removed. An electric shock fuses them and starts division by mitosis. The embryo is implanted into a surrogate mother, and the offspring is genetically identical to the nucleus donor.
Cloned transgenic animals are animals, such as sheep or goats, that carry a human gene and are cloned to make many identical copies. They produce human proteins, often in their milk, where the protein is collected and purified. Examples are alpha-1-antitrypsin, used to treat emphysema, and blood clotting factors, used to treat haemophilia.
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Quick check questions
What is micropropagation?
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Growing new plants from explants in vitro, on sterile nutrient medium.
What are the small pieces of plant tissue used in micropropagation called?
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Explants.
What type of nucleus is put into the enucleated egg cell to clone a mammal?
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A diploid nucleus from a mature body cell.
Name a human protein made by cloned transgenic animals.
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Alpha-1-antitrypsin (or a blood clotting factor).
Frequently asked questions
What is micropropagation and why is it used?
Micropropagation is growing new plants from small pieces of tissue called explants on sterile nutrient agar containing plant growth hormones. It is used because commercial quantities of genetically identical plants are produced quickly from a small amount of tissue, so plants with desirable characteristics are copied exactly, all year round and in a small space.
How was Dolly the sheep cloned?
Dolly was cloned by taking a diploid nucleus from a mature udder cell of an adult sheep and putting it into an enucleated egg cell. An electric shock fused them and started the egg dividing by mitosis. The embryo was implanted into a surrogate mother, and Dolly was genetically identical to the nucleus donor.
How are cloned transgenic animals used to produce human proteins?
A human gene for a useful protein is inserted into an animal cell, such as from a sheep or goat, and the cell is cloned by nuclear transfer. The transgenic animal makes the human protein in its milk, where it is collected and purified. Cloning gives many identical animals that all make the protein.
Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026