Scientists are looking for 100,000 volunteers prepared to have their DNA sequenced and published online for anyone to look at.

The UK Personal Genome Project could provide a massive free tool for scientists to further understanding of disease and human genetics.

Participants will get an analysis of their DNA, but so will the rest of the world, and anonymity is not guaranteed.

They are warned there could be unknown consequences for them and relatives.

Unlocking the secrets of DNA could transform the understanding of disease.

There is potentially huge public benefit, but there is the potential for it to rebound, but how that rebounds on the person, families and those yet to be born is very difficult to know Dr Peter Mills, Nuffield Council on Bioethics

A deeper understanding of Alzheimer's disease is emerging by looking for differences in the DNA of people with and without the disease.

Prof George Church, who runs the US version of the project, said analysing 100,000 genomes could lead to advances in common diseases such as diabetes.

He said: "We're finding more and more of these common diseases are a collection of rare diseases.

"Cancer used to be a disease, then it broke up into lots of different diseases by tissue, then lots of sub-categories based on the genes that are impacted, so now it's thousands of diseases."

Participants will have to pass tests to prove they fully understand the risks of making their genetic identities freely available for the world to use before taking part.

There will be immediate risks and those that emerge as genetic technology advances including:

finding out about a genetic disease

a partner being put off by a higher risk of Alzheimer's or other illnesses

targeted advertising or insurance premiums based on genomes

cloning without permission

copies of DNA being used to implicate people in a crime

Family factor

Dr Peter Mills, who is investigating the ethical issues around biological and health data with the Nuffield Council on Bioethics, told the BBC: "The difference with genetic data is you're not just committing yourself to something you might not fully envisage, but you're also implicating biological relatives.

Human Genetics Alert would strongly advise people not to give their genetic information to a project which will share it with the world Dr David King, Human Genetics Alert

"There is potentially huge public benefit, but there is the potential for it to rebound, but how that rebounds on the person, families and those yet to be born is very difficult to know."

Cian Murphy, a 24-year-old PhD student at University College London, wants to take part. He said: "Very few people live their whole lives not affected by some genetic illness, your sample could be the difference between a cure being discovered or not."

As part of the study, participants will find out intimate details about their genome, such as the presence of any high-risk breast-cancer genes.

They will be given a list of doctors they can go to if they need further medical advice.

While people will not have their name published, studies have shown it is possible to work out someone's identity from genetic databases and other public records.

Dr David King, from the group Human Genetics Alert, said: "Human Genetics Alert would strongly advise people not to give their genetic information to a project which will share it with the world.

"Once your data is online, you will never be able to recall it. The project's informed-consent procedures are not valid, because they do not tell you all of the risks. That is not informed consent."

He warned the data could be used for any purpose including those people objected to ethically and said there was "no reason" for it to be public.

More genomes

Meanwhile, the government's Genomics England project is trying to sequence 100,000 NHS patient's DNA, which is private and carries a threat of legal action if patients are identified.

Sir John Chisholm, executive chairman of Genomics England, said: "We would want anyone consenting to their DNA being used for sequencing to have a clear understanding of what they are contributing to, and to do so on a voluntary basis which we understand will be the case with Personal Genome Project.

"Anyone who takes part in any initiative that involves giving a DNA sample for sequencing should be as clear at the time of giving their consent as they can be of how that sample will be used, and who will have access to it, and what future purposes it can be put to."