perfidy

Geneticists have completed a map of the common variations in the human genome. Sadly, this will not immediately lead to technology that would make our brains, muscles or, uh, units bigger. However, it is a major step forward in our understanding of what actually makes us tick. The HapMap, as it is called, is a sort of a complement for Craig Venter's human genome project. Where the human genome project detailed the genetics that all humans have in common, the HapMap details the genes that make us different.

As scientists dig into the details, it is expected that we may begin to get a handle on how genes can contribute to disease. In the past, single genes have been linked to rare disorders, but the technology did not exist to look at patterns in large numbers of genes. Analysis of the data in HapMap may lead to stunning advances in medical treatments.

The idea behind the map is rather clever, as we would expect of highly paid genetic scientists. There are over three billion letters in the human genetic code. That's a lot, and presents a problem for researchers trying to track down subtle interrelationships between genes. However,

Each person differs from someone else by, on average, 3 million of these units, but every time two people are compared, it is a different set of 3 million. To find all those differences, scientists had feared they would need to determine the full genome, all 3 billion units, of every volunteer in a study, which would be too expensive using current technology.

But then researchers began to notice consistent patterns in the DNA of different individuals that suggested a shortcut, said Mark Daly, a scientist at Mass. General and the Broad who was one of the first to discover the patterns. They found that DNA can be thought of as a series of sections, called ''haplotype blocks." Each block comes in only a handful of variations, and each person has just one of the variations. (Each of these variations is known as a haplotype, which is why the map is known as the HapMap.)

To determine which block a person has, researchers have only to look at one spot where the block varieties are different, giving them a ''tag" that identifies the block.

So instead of laboriously trawling through billions of units, only a relative few need to be checked. Maybe we'll beat the robots yet...

And maybe, we can all get tiger-shaped eyes. 'Cause that would be so cool!