By Ivan Noble BBC News Online science staff

Decoding using the power of robotics and computers (Image by The Wellcome Trust Sanger Institute)

Their announcement came less than three years after a "rough draft" was published to worldwide acclaim.

When UK Prime Minister Tony Blair and then US President Bill Clinton hailed the publication of the draft in June 2000, 97% of the "book of life" had been read.

The decoding is now close to 100% complete. The remaining tiny gaps are considered too costly to fill and those in charge of turning genomic data into medical and scientific progress have plenty to be getting on with.

The Wellcome Trust Sanger Institute, the only British institution taking part in the international effort, completed almost a third of the sequence - the biggest contribution by a single institution.

Its director, Professor Allan Bradley, said that completing the human genome was a vital step on a long road, but that the eventual health benefits could be phenomenal.

"Just one part of this work - the sequencing of chromosome 20 - has already accelerated the search for genes involved in diabetes, leukaemia and childhood eczema.

"We shouldn't expect immediate major breakthroughs but there is no doubt we have embarked on one of the most exciting chapters of the book of life," he said.

High standards

American institutions have been the major partners in the decoding programme.

THE DNA MOLECULE The double-stranded DNA molecule is held together by chemical components called bases Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G) Groupings of these letters form the "code of life"; there are about 2.9 billion base pairs in the human genome wound into 24 distinct bundles, or chromosomes Written in the DNA are 30,000-40,000 genes which human cells use as templates to make proteins; these sophisticated molecules build and maintain our bodies

Dr Francis Collins, director of the National Human Genome Research Institute, US, also pointed to the long-term gains that would come from the information.

"One of our projects is to identify genes that predispose to type II diabetes.

"This disease affects about 1 in 20 people over 45 and its incidence appears to be increasing. Using freely available map and sequence information [we] have been able to close in on the likely gene on chromosome 20 that is altered in type II diabetes."

When the Human Genome Project was formally launched, there were some who thought it could take 20 years or more to complete. But robotics and supercomputers speeded up the process hugely.

And it is arguable that competition from a privately funded company, Celera Genomics, which produced a rival sequence, hastened the end stages of the project as well.

The purpose of the last three years has been to fill in gaps in the DNA sequence and "proof read" the data to produce a "gold standard" that will inform genetic research for years to come.

Dr Jane Rogers, head of sequencing at the Sanger Institute, said: "We have reached the limits we set on this project, achieving tremendously high standards of quality much more quickly than we hoped.

The model of DNA built by Crick and Watson (Image by the Science Museum)

"The working draft allowed researchers to kick-start a multitude of biomedical projects. Now they have a highly polished end product which will assist them even more.

"It's a bit like moving on from a first-attempt demo music tape to a classic CD," she said.

Knowing virtually the entire sequence of the roughly three billion letters of genetic code in our DNA gives scientists the chance to explore everything that is genetically determined about our lives.

Sir John Sulston, who ran the British end of the project for much of its history, said earlier in April that researchers would "go on mining the data from the human genome for ever".

And DNA pioneer James Watson told a press conference on Monday "When we know the face of the enemy... we will try to cure the disease or lessen its effects".

Identifying genes can now be done in days instead of years. But for medicine, the real challenge is to move from knowing which malfunctioning gene or genes cause a particular condition to knowing how to do something about it.

For this, they will need to understand better how the proteins - the sophisticated molecules which cells make from the gene "templates" - interact to build and maintain our bodies.

The science of genomics may be well established but the science of proteomics is still in its infancy.

There is, as Professor Bradley said, "a long road" to travel.