The health-conscious will be able to learn whether they are likely to contract inherited diseases with the launch of a service that will let them explore their DNA.

For $1,000, US customers will be able to send off a sample of their saliva to a Californian company and receive a 'genetic profile' based on an analysis of more than half a million points on their genome.

The report - which is accessed online - will identify similarities between the customer's genes and those associated with about a dozen diseases and conditions, including type 2 diabetes and Crohn's disease. In turn, the company hopes, customers will be able to take 'preventive action' in relation to their health.

23andMe, one of whose founders is married to the co-founder of Google, Sergey Brin, is one of a number of firms aiming to capitalise on their new market for personalised healthcare, where companies aim provide tailored, genetic information to customers.

Last week, DeCode Genetics, an Icelandic firm, began a similar service for North American and European customers costing $985, and another Californian company, Navigenics, is also due to enter the market soon.

"Our mission is to take the genetic revolution to a new level by offering a secure, web-based service where individuals can explore, share and better understand their own genetic information," Linda Davey, one of 23andMe's co-founders, said.

Genetics experts criticised the service, saying that for the vast majority of customers it would be "scarcely of any use at all," and that 80 per cent of the information relevant to a determination about a customer's life expectancy, say, could be ascertained in a doctor's appointment.

They said that with many inherited conditions - Alzheimer's, for instance - genes which indicated a pre-disposition varied hugely across populations, and that just because a person knew they were predisposed to a condition did not mean they could expect better treatment.

"Genetics has principally been a diagnostic tool, not a form of treatment," Steve Jones, a professor of genetics at University College London. "These DNA-based services are for the most part making the obvious expensive."

Professor Jones added that 95 per cent of new breast cancer cases were not caused by either of the two genes - BRCA1 and BRCA2 - known to cause a predisposition to the disease.

Dr Fred Kavalier, a spokesman for the British Society for Human Genetics, said: "Genetics is an extremely complicated field, and we simply don't have sufficient information to be able to predict people's risk of develping disease based on a reading of their genetic profile."

23andMe's service has three components - Genome Labs, which lets customers pick through the 'raw catalogue' of their 23 pairs of chromosomes; Gene Journals, which lets them match their genome with current research into inherited conditions; and Ancestry, where there can share profiles with family members and trace the origin of particular traits.

In May Google announced that it had invested $3.9 million in 23andMe, one of whose directors, Anne Wojcicki, is married to Google's co-founder, Sergey Brin.

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