The genome of an organism is the complete set of its genetic material. The Human Genome Project worked out the order of the bases in human DNA and located the genes. This helps scientists find the alleles that are linked to disease.
One use is to predict the likelihood of disease. If a genetic test finds an allele linked to a higher risk of a disease, such as some cancers or heart disease, the person has a greater chance of developing it. This is a probability, not a certainty, because most diseases are affected by several genes and by lifestyle. Knowing the risk early lets a person change their lifestyle or have regular screening, so a problem can be found and treated sooner.
A second use is treatment. In personalised medicine, doctors can choose drugs that are targeted to a patient's genome. The drug is more likely to work and is less likely to cause side effects.
There are concerns. A person may become anxious about a disease they might never get, or learn of one that cannot be treated. Genome information also raises questions of privacy, for example whether insurers or employers should be allowed to see it.