Paul Nurse: We are made of more than just our genes

Genetic testing is rapidly moving out of the realms of science fiction and into our everyday lives. There are now genetic tests for cancer and heart disease, with many more in the pipeline. The ability to peer into our genetic destinies us is potentially a force for good, but without proper debate I fear that these tests could lead to a kind of "genetic apartheid", with people discriminated against because of DNA defects.

Genome sequencing – deciphering the "code book" of all the 30,000 or so genes each person has – has developed at a rapid pace. In 1985 it took three years to decode a single gene, yet now we can sequence the entire human genome. The American scientist Craig Venter is already offering the very rich the chance to buy a map of their genomes at a staggering $710,000, but even he anticipates selling them for much less – $1,000 – in years to come.

Genetic testing could lead to an era of personalised medicine and better-tailored preventive treatment. But genes alone do not make the man or woman. There are some conditions – such as Huntingdon's disease and cystic fibrosis – that are caused by a mutation in a single gene, where a genetic test can tell without a doubt that a person will develop the disease in later life.

But most genetic tests, however, can only show an increased risk, not a certainty of developing the disease. Women with defects in the BRCA1 and BRCA2 genes, for example, will not definitely get breast cancer. And even the age of onset for Huntingdon's disease varies enormously.

Whatever your genes, environmental factors play a very significant role in future health. Given this complexity, employers and insurers will find it difficult to use genome sequences meaningfully when deciding who to employ or the level of premiums. Results could be interpreted simplistically and lead to a new form of unfair discrimination.