The genome is all the genetic material in an organism. The Human Genome Project, completed in 2003, worked out the sequence of bases in human DNA and found the genes it contains. This lets researchers identify genes linked to inherited diseases.
One use is predicting the likelihood of a disease. Some people carry alleles that increase their risk. For example, the BRCA1 and BRCA2 alleles raise the risk of breast cancer and ovarian cancer. A genetic test shows the likelihood of getting a disease, but not that a person definitely will, because lifestyle and the environment also matter. People who know their risk can have regular screening, change their lifestyle or choose preventive surgery.
Understanding the genome can also improve treatment. People respond differently to the same drug because of differences in their genomes. Drugs targeted to a person's genome, called personalised medicine, can work better and cause fewer side effects. Doctors can choose the right drug and dose first time.
There are risks too. Genetic information could be misused by insurers or employers, and test results can cause worry, especially for diseases with no cure.