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James Watson and Francis Crick

DNA was first discovered in the mid-19th century, but its function remained a mystery. In the early 1950s two scientists, Rosalind Franklin and Maurice Wilkins, studied DNA using X-rays.

Franklin produced an X-ray photograph that allowed two other researchers, James Watson and Francis Crick to work out the 3D structure of DNA. The structure of DNA was found to be a double helix.

Crick and Watson’s model served to explain how DNA replicates and how it carries genetic information in humans. This set the stage for the rapid advances in molecular biology that continue to this day. Molecules carry the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms.

Human Genome Project

The genetic information in an organism is called its genome. The Human Genome Project (HGP) started at the end of the 20th century. It involved scientists from 18 countries and showed the importance of collaboration in advancing medical knowledge. It was very ambitious and had several aims, including:

• working out the sequence of all the three billion base pairs in the human genome
• identifying all the genes
• developing faster methods for sequencing DNA

The sequencing project was finished in 2003, and work continues to identify all the genes in the human genome.

Modifying DNA

By modifying DNA it is possible that genetic diseases can be eliminated. DNA can be used to screen people for genetic diseases, eg breast cancer. It has also been used to reverse mutations that cause blindness, to stop cancer cells from multiplying and make some cells resistant to AIDS.