What rDNA technology has given us

Before rDNA technology, some medicines were very hard to get:

• A few milligrams of insulin needed tons of pancreas glands from slaughtered animals.
• Growth hormone, used to treat dwarfism, needed thousands of pituitary glands.

So supply was small, the cost was high, and animal proteins could cause immune reactions in people, because the body sees them as foreign.

Now human insulin and human growth hormone are made by bacteria carrying the human genes: plentiful, cheaper, and identical to the body's own. Many other products followed:

• Interferon, used to treat some cancers.
• Plasminogen activator and urokinase, which dissolve blood clots.
• Vaccines: Recombivax HB against hepatitis B (1986), and Gardasil against HPV (2006).

In farming, scientists can make targeted changes to a crop's genes. Genetically modified (GM) plants can resist disease, survive drought, or tolerate salty soil, improving both their quality and their value. Well-known examples are the Flavr Savr tomato (which stays firm longer), Bt cotton (grown in India since 2003) and Golden Rice.

In the future, plants may be used to make medicines: therapeutic proteins, peptides and hormones. These would cost less than products from animals, and would avoid contamination with animal viruses and proteins.

The next chapters look at the parts of rDNA technology one by one: the host and vector, the steps of gene cloning, and its applications.