They have completed a map that charts patterns of human genetic variation in the world population, to better understand human biology, evolution and how to diagnose diseases.
  
"It is a scientific milestone because it now links directly to the human genome sequence and provides a tool to streamline genetic studies," said Dr Panos Deloukas, of the Wellcome Trust Sanger Institute in an interview on Wednesday.

The Human Genome Project, which mapped the three billion letters that make up the human genetic code, showed that any two people are 99.9% the same.

Now an international consortium of scientists has completed a more detailed chart, or HapMap, showing markers of genetic variation, or single nucleotide polymorphisms (SNPs), to explain the 0.1% difference. 

Probing diseases
   
The HapMap shows SNPs are grouped in neighbourhoods, or haplotypes, and are usually inherited as blocks of information.
   
"People around the world are using these markers to do genetic association studies to understand the molecular basis of common diseases," added Deloukas, who worked on the project.
 
The International HapMap Consortium, a public-private partnership of 200 scientists from Britain, the United States, Canada, Japan, Nigeria and China developed the HapMap using DNA samples from 269 people from Asia, Africa and the United States.
   
The first phase of the HapMap, which is published in the science journal Nature, contains more than 1 million SNPs. A second phase will add another 2 million.
  
"The human genome sequence provided us with the list of many of the parts to make a human. The HapMap provides us with indicators - like Post-It notes -which we can focus on in looking for genes involved in common diseases," said Professor Peter Donnelly, of Oxford University in England. 

"It is a scientific milestone because it now links directly to the human genome sequence and provides a tool to streamline genetic studies"

Panos Deloukas,
Wellcome Trust Sanger Institute

Using the HapMap, scientists can compare SNP patterns in people with an illness to healthy individuals to identify its underlying genetic causes. 

Greater insights
   
"It will also help us understand other important processes in biology like evolution, recombination and the forces that have shaped this genetic variation in the human population," said Deloukas.
   
Recombination is the joining of DNA from maternal and paternal lines. The HapMap data will allow scientists to do more detailed studies of inheritance.
   
It has already revealed that genes involved in DNA repair are not as diverse as those which play a role in the body's immune response.
   
"A number of labs around the world are setting up experiments," Deloukas said. "In the next two to three years we should see a real wealth of information coming out of these studies. 
  
"Clearly it is going to accelerate the identification of the molecular basis for common diseases dramatically."