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DNA was first discovered in the mid-19th century, but its function remained a mystery.

James Watson and Francis Crick

In the early 1950s, two scientists - Rosalind Franklin and Maurice Wilkins - studied DNA using X-rays.

Franklin produced an X-ray photograph. In 1953, this 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.

Watson and Crick’s model explained how DNA replicates and how it carries genetic information in humans. For example, this information controls:

• growth
• development
• function
• reproduction

This set the stage for the rapid advances in molecular biology that continue to this day.

Human Genome Project

The genetic information in an organism is called its genome. The Human Genome Project was 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 3 billion base pairs in the human genome
• identifying all human genes
• developing faster methods for sequencing DNA

The sequencing project was finished in 2003. Work continues today to identify all the genes in the human genome.

Modifying DNA

By modifying DNA, it may be possible to eliminate genetic diseases in humans. 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 to make some cells resistant to AIDS.