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The genome of an organism is the entire genetic material of that organism. Each of your diploid body cells (not sperm, eggs or red blood cells) has one copy of your entire genome.

The Human Genome Project started in 1990 and was completed in 2003. Hundreds of scientists from different universities all over the world collaborated together to determine the sequence of base pairs that made up the genome of a random man and woman. There are more than three billion of these! This was a huge moment in the history of biology, and one that showed the importance of working together and sharing scientific information.

The mapping of the whole human genome has great importance for medicine. In order to exploit its secrets, it is vital that the human genome is fully understood. It enables us to:

• search for genes linked to different types of disease
• understand inherited disorders and their treatment
• trace human migration patterns from the past

Scientists are now searching for disease associated genes within the human genome. Two examples of these are genes that can contribute to breast cancer, which are known as BRCA1 and BRCA2. Mutations in these genes account for approximately 10% of all inherited breast cancer cases detected.

Scientists detected BRCA1 and BRCA2 genes by studying families where breast cancer was known to have been inherited between individuals. They were able to create a pedigree analysis, which is similar to a family tree diagram that showed the close relationship of those affected and unaffected within the family.

The pedigree analysis illustrates the inheritance pattern of the disease to be determined. This enabled scientists to test DNA from the affected and unaffected individuals to identify differences. It is now possible to detect the presence of the genes by having a simple blood test.