Asexual reproduction

Plants can make identical copies (clones) of themselves. Many plants have ways of increasing their numbers by asexual reproduction – new plants are created by repeated cell division:

 A potato plant can produce many tubers, each of which can grow into a new plant.

• Strawberry plants and spider plants produce long stems with tiny plants on the end. These runners can produce several new plants from one parent.

It's fairly easy to artificially produce new plants by taking a cutting, and waiting for the cutting to develop new roots and leaves.

The stages of cloning

In 1996 the first large animal was cloned. It was called Dolly, the sheep. Many attempts had been made before the stages of cloning were properly understood. The stages include:

• Removal of diploid nucleus from a body cell
• Enucleation, or removal, of egg cell
• Insertion of diploid nucleus into enucleated egg cell
• Stimulation of the diploid nucleus to divide by mitosis

How Dolly the sheep was cloned

In this famous example of cloning, an ordinary cell was used to replace the nucleus of an egg cell, so all of Dolly's cells had identical DNA to the one parent that donated the cell. This form of cloning produced a single, genetically identical, offspring.

Ethical issues

Animal cloning raises ethical issues about how far humans should be allowed to interfere in the production of new life. Regulations currently restrict scientific research into human cloning.

Cloning plants is easier than cloning animals. Cloning expensive food crops has been carried out for many years, and causes the public fewer ethical and moral concerns than animal cloning.

Advantages and disadvantages of cloning

How to clone cows using embryo transplants

This technique could be used to make many copies of cows that have a high milk yield. It would produce a herd of cows much faster than if the original cow was used for breeding in the normal way. Sexual reproduction is still involved and the calves are not identical to either parent.

Producing many genetically modified pigs

Pigs may be able to grow replacement organs for use in human transplant surgery. The pigs would first have human genes inserted into their cells so that the organs would not be rejected when…