The most exclusive status symbol around is owned not by a super-rich playboy, but by a couple of scientists. While it should soon be possible to sequence anybody's entire genetic code for as little as £1,000, the only people who have yet had the privilege of reading every letter of their DNA are Jim Watson and Craig Venter.

The pair may well be the best-known living geneticists - and certainly the most controversial. Watson, the co-discoverer of the double-helix, is famously outspoken and politically incorrect. Venter, whose private effort to map the human genome triggered the fiercest scientific row of the past decade, is now attempting to create artificial life.

One of the first comparisons of their DNA, published yesterday by Venter's research team, does not reveal whether the two men share genes that explain their almost limitless capacity for starting fights. But it has shed important light on one of the main ways in which genetics might improve public health: predicting how patients will respond to drugs.

How the human body metabolises medicines depends heavily on genes, particularly those in a group called the CYP family. Variants that people inherit explain why some need very high doses of the blood-thinner warfarin that would be life-threatening to others. Others can predict how people will do when given antidepressant or antipsychotic drugs.

It is also known that these genetic variants differ in frequency between different ethnic groups, and this can be a useful tool for doctors. Venter, however, has always doubted whether race is a meaningful concept in science and medicine. His team's comparison of his genome and Watson's, published in Clinical Pharmacology and Therapeutics, illustrates why.

Both men are white, and might be expected by the rules of ethnic medicine to have the same CYP genes. But they don't. Venter has variants that suggest his body is good at processing antidepressants and the painkiller codeine. Watson's genome suggests he would respond less well, and might need higher doses for effective treatment.

No doctor would have guessed this from the colour of their skin. While race can be a helpful proxy for genes, it is an unreliable one. Ethnic medicine thus risks denying patients a helpful drug, because their genes do not match the group norm. It will also soon be obsolete, because Venter and Watson are not going to remain the only people with personal genetic read-outs for long. The cost of sequencing a genome is already down to about £30,000. As it falls further, it will become possible to prescribe to all patients according to their genes instead of their race.

Venter's new study certainly highlights the medical value of doing this, but I'm sure that isn't the only reason why he began it. He will also have been delighted to tweak his rival's tail. Jim Watson, you may remember, has expressed rather unsavoury views on race: last year, he suggested that Africans are less intelligent than Westerners. Venter, who was one of his biggest critics, has now used Watson's own genome to show up the limits of racial stereotyping. There is mischief as well as mastery in this man's science.

Horses for courses

Defenders of the Prince of Wales's rant against GM crops have seized on a recent document called the International Assessment of Agricultural Science and Technology, which they claim has clinched their case.

This exercise indeed concluded that GM is not the only answer to the world's food problems - but that isn't a claim that serious plant scientists actually make. To ask whether GM is the solution to global hunger is like asking whether cars are the best method of transport: it depends where you're going. For a journey of a hundred miles or so, say London to Norfolk, you probably would take to the road. But you wouldn't drive to New York, or next door to borrow some milk.

Plant transgenics is much the same. For designing salt-tolerant crops, GM may be the best option. For others, traditional breeding can do the job better. It would be foolish to discard either tool because it can't do everything.

Nothing to declare

Though the Beijing Olympics have so far brought few drug scandals, it would be naive to think that some athletes have not been doping. But have any of them been placebo doping?

It isn't necessary to take an illegal drug to derive a performance-enhancing benefit: simply thinking that you're taking one can also have an effect. In a recent study at the Garvan Institute in Australia, athletes were told they were being given human growth hormone, but actually received an inert replacement. They still ran faster and jumped higher than before.

So couldn't a coach convince a competitor that she was taking drugs, while actually giving her a sugar pill? She'd gain from the placebo effect, while sailing through doping controls. Would she be cheating?

Mark Henderson is science editor of The Times

Times Recommends

• Nerdy cafés no longer maid in heaven
• Cameron will not break marriage vow
• Avatar will make the case on climate