Large amounts of DNA are needed for genetic engineering. Multiple copies of a piece of DNA can be made either by using polymerase chain reaction (PCR) or by cloning DNA in cells.

Get information sheet: Polymerase chain reaction (PCR)

How is DNA cloned in cells?

DNA cloning

To get multiple copies of a gene or other piece of DNA you must isolate, or ‘cut’, the DNA from its source and then ‘paste’ it into a DNA vector that can replicate (or copy) itself.

The four main steps in DNA cloning are:

Step 1. The chosen piece of DNA is ‘cut’ from the source organism using restriction enzymes.

Get information sheet: Restriction enzymes

Step 2. The piece of DNA is ‘pasted’ into a vector and the ends of the DNA are joined with the vector DNA by ligation.

Get information sheet: DNA ligation

Step 3. The vector is introduced into a host cell, often a bacterium or yeast, by a process called transformation. The host cells copy the vector DNA along with their own DNA, creating multiple copies of the inserted DNA.

Get information sheet: Bacterial transformation

Step 4. The vector DNA is isolated (or separated) from the host cells’ DNA and purified.

DNA that has been ‘cut’ and ‘pasted’ from an organism into a vector is called recombinant DNA. Because of this, DNA cloning is also called recombinant DNA technology.

What is cloned DNA used for?

DNA cloning is used to create a large number of copies of a gene or other piece of DNA. The cloned DNA can be used to:

• Work out the function of the gene
• Investigate a gene’s characteristics (size, expression, tissue distribution)
• Look at how mutations may affect a gene’s function
• Make large concentrations of the protein coded for by the gene

What other types of cloning are there?

The term ‘cloning’ is also used to describe other laboratory processes:

• Reproductive cloning is the process of making a genetically identical copy of an organism.
• Therapeutic cloning is the process of making multiple copies of a cell to treat a disease.