The genetic differences between individuals are to be mapped in unprecedented detail in the most comprehensive search yet for the inherited roots of common conditions such as heart disease and diabetes.

The 1,000 Genomes Project, announced yesterday by an international consortium of scientists, aims to identify every genetic variant carried by at least 1 per cent of mankind, to unlock how they influence health.

When the map is complete, in two years, it will include the genetic codes of more than a thousand individuals, providing an index to the human genome. It will give geneticists instant access to all the reasonably common variations that exist in any given stretch of human DNA, allowing them to pinpoint genes that affect people’s risk of particular diseases far more quickly than is now possible.

Scientists have long been able to find very rare genetic mutations with severe effects, such as those that trigger Huntington’s disease or cystic fibrosis. A newer tool called genome-wide association has also enabled them to trace common variations carried by about 10 per cent of the population. About 100 of these have moderate effects on conditions such as diabetes and heart disease.

The 1,000 Genomes Project will now make it possible to identify “medium-rare” genetic variants that are carried by about 1 in 100 people. “Between these two types of genetic variants — very rare and fairly common — we have a significant gap in our knowledge,” said David Altshuler, of the Broad Institute in Massachusetts, a co-chairman of the project.

All human beings are more than 99 per cent similar at the genetic level, but the small stretches of DNA that vary between individuals often explain differences in susceptibility to disease.

Genome-wide association studies search for variations that influence health by comparing thousands of people who have a certain disease with healthy controls. Scientists then look at 500,000 genetic markers, to determine which are much more common among people with the disorder.

But these markers are not always part of the genes that cause health effects, but rather highlight sections of DNA in which the genes might lie. As a result, extensive follow-up studies are often needed. The 1,000 Genomes Project will shorten this process.

The campaign against a proposed law that would block many experiments with cloned embryonic stem cells has been backed by a further 29 senior medical researchers and administrators. The Government agreed to reconsider the Bill on Monday, after a letter to The Times in which experts cautioned that requiring explicit consent would threaten research.

Filling in the gaps

— The completed human genome map was published in 2003. Work continues on filling in small gaps

— The 1,000 Genomes Project will chart the genetic variants carried by at least 1 per cent of the population. It will include genetic material from ethnic groups including Yoruba in Nigeria, Japanese, Chinese, Utah residents with ancestry from northern and western Europe, Luhya from Kenya, Masai from Kenya (pictured), Toscani from Italy, Gujarati Indians from Houston, Texas, people of Mexican ancestry in Los Angeles, and people of African ancestry in the southwestern United States

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