Scientists have published data on over one million crucial DNA variations in three racial groups, paving the way for "individualised" medicines.
Since a drug may work better for some people and not others, doctors could eventually use blood tests to provide targeted treatments for each patient.
But others fear the information could be used to discriminate against people on the basis of their genes.
Details of the research, by a team from California, appear in Science magazine.
The team looked at single-nucleotide (or "letter") polymorphisms (SNPs), which are points in DNA that vary between different individuals.
The mapping effort describes 1.58 million of these single-letter DNA variations across 71 people of European-American, African-American and Han Chinese ancestry.
"People may pick people based on the colour of their skin, but they will find entirely different groups of people when they look at the genetics"
He was describing his team's work at the annual meeting of the American Association for the Advancement of Science (AAAS), gathered this year in Washington DC.
He added that the results might yield useful applications within five years.
By comparing the DNA of people who have had a good response to a drug with those who have had a bad side-effect, scientists can develop tests to target drugs to individual patients.
"By finding the differences in those groups of people, and then repeating it, you will have a kind of barcode for an individual person that can be used by their doctor," Dr Cox explained.
"You'll come in, the doctor will look at you, see that you have high blood pressure, come back to you and say: 'This is the drug to take'."
Easy to abuse?
The mapping data also shows up the genetic variation between populations such as Europeans and Han Chinese.
This has sparked fears that the information could be used to look at the prevalence of genes for traits such as intelligence or criminal behaviour in particular populations - possibly leading to discrimination.
DNA IN HUMAN CELLS
Dr Cox agreed there was scope for abuse, but he added that it was impossible to place individuals into categories on the basis of their affiliation to one group because of the large genetic differences within all human groups.
However, Troy Duster, director of the Institute for the History of the Production of Knowledge in New York, US, warned the work could serve to reinforce misconceptions about racial groupings.
"The particular groups of individuals chosen to represent each region of the world are often chosen because of their convenience and accessibility," he wrote in Science.
"If we fall into the trap of accepting the categories of stored data sets, then it can be an easy slide down the slope to the misconceptions of 'black' or 'white' diseases."
But Dr Cox argues that his work could actually help demolish established views of race.
"We put people into bins based on what they look like, trying to predict what's going to happen. But these are surrogates of what's actually going on inside our bodies," he explained.
"People may pick people based on the colour of their skin, but they will find entirely different groups of people when they look at the genetics - not based on what they look like, but how their bodies work."
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