CloningEdexcel IGCSE Biology: Revision notes

A clone is an organism that is genetically identical to its parent. Cloning happens naturally in some organisms (e.g. asexual reproduction) but can also be carried out artificially using two main techniques covered here: micropropagation in plants and cell/nuclear transfer cloning in mammals.

Micropropagation is a method of cloning plants:

1. Small pieces of plant tissue, called explants, are taken from a parent plant with desirable characteristics
2. The explants are sterilised and grown in vitro (in a sterile nutrient medium, in test tubes/dishes)
3. Plant growth hormones stimulate the explants to develop into complete new plantlets, genetically identical to the parent
4. The plantlets are gradually acclimatised and transferred to soil

Micropropagation allows commercial quantities of genetically identical plants with desirable characteristics (e.g. disease resistance, high yield, attractive flowers) to be produced quickly, all year round, and independent of seasons.

Cloned mammals (illustrated by Dolly the sheep) are produced by somatic cell nuclear transfer:

1. An egg cell is taken from a donor animal and its nucleus is removed (enucleated)
2. A diploid nucleus is taken from a mature (adult body/somatic) cell of the animal to be cloned
3. This diploid nucleus is inserted into the enucleated egg cell
4. The cell is stimulated (e.g. with an electric shock) to begin dividing, forming an embryo
5. The embryo is implanted into the uterus of a surrogate mother, which carries the pregnancy to birth

The resulting offspring is genetically identical to the animal that donated the diploid nucleus, not the animal that donated the egg cell or the surrogate mother.

Once a transgenic animal (one containing a gene from another species) has been produced, cloning allows many genetically identical copies to be made. Cloned transgenic animals can be used to produce human proteins, for example a transgenic goat engineered to produce a human protein in its milk, which is then extracted and purified for medical use.