The world depicted in the cautionary film, Gattaca, is not far away, but says Tom Wilkie, we can still choose a different future
I share a genetic defect with the lead character of Gattaca, the film about DNA-based discrimination which went on general release yesterday. It's a common condition, usually regarded as trivial, but I've always been sensitive about it. In the Orwellian world of Gattaca, set in the not-too-distant future, people like me would not be allowed. Or rather, we would be allotted a lowly place in the social and economic rungs of society, consigned by our genetic make-up to an untouchable caste.

Gattaca is a cool, stylish thriller set in a society where people have come to believe that DNA is destiny - that our futures can be mapped out in our genes. There is certainly precedent for that: no less a person than Jim Watson, the co-discoverer of the double helix of DNA itself, told Time magazine in 1989, "We used to think our destiny was in the stars. Now we know it's in our genes."

Into this society comes an impostor, Vincent Freeman, whose life ambition is to travel into space on a mission to Titan, the largest of Saturn's moons. But Vincent was conceived in the American way, in the back seat of a car, and the roll of the DNA dice has left him short of the genetic gold standard required of astronauts. No efforts he can make by himself will remove the modern marks of Cain.

By the time of his younger brother, however, their parents' passion is under control and they conceive lots of embryos by in-vitro fertilisation (IVF), selecting only the genetically most healthy for implantation into the mother's womb. Gattaca is a world of designer babies, achieved not by sophisticated genetic engineering, but by a plausible extension of what is already being practiced. In Britain today, some embryos conceived through IVF are already having their genes checked and selectively implanted. This pre-implantation diagnosis is being carried out under strict regulation (in this country at least) and for the most honourable of motives. Some mothers at risk of having boys with the devastating genetic disorder Duchenne Muscular Dystrophy have elected to have only female embryos implanted because the disorder, like haemophilia, is expressed only in males.

But in a little noticed speech just before Christmas, one of this country's outstanding geneticists, Professor Peter Goodfellow, told a meeting of the Genetic Interest Group (the support organisation for families with genetic disorders) that it might be possible within 20 years to read out not just a few disease-related genes during pre-implantation diagnosis, but an embryo's entire genetic make-up - blue eyes, fair hair, the lot. And not only would it be possible, it would be cheap. Science, it would appear, will imitate art.

In the film, to subvert the system and realise his ambition to "slip the surly bonds of Earth to touch the face of God", Vincent colludes with a champion athlete, Jerome, to use samples of Jerome's DNA to deceive the oppressive and all-pervasive identity checks. Vincent wears a pad containing Jerome's blood on his forefinger to beat the entry system to the space headquarters. Staff have to pass daily through turnstiles that automatically take a minute blood sample from a finger-prick and produce a DNA-fingerprint to check identity.

Here, art is imitating politics. In July 1996, Frank Field, now junior minister in the Department of Social Security, wrote a polemic in the Sunday Mirror advocating that benefits claimants should be genetically fingerprinted so as to avoid social security fraud: "Your number's up! Why DNA testing can beat the welfare cheats".

Jerome was born with all the best genes, but they did not protect him from a road accident that left him crippled, wheelchair-bound, and without a role in this brave new world. He fulfils his destiny vicariously by selling his genetic samples to Vincent who officially becomes Jerome (who retreats to use his middle name, Eugene - a pun on eugenics meaning "well- born"). The name's hand-over is symbolic (Jerome means "sacred name") and the film's title too is a pun, deriving from the four key chemicals in DNA - guanine, adenine, thymine, and cystosine - whose acronym spells GTCA.

As the relationship between Vincent/Jerome and Jerome/Eugene grows beyond a mercantile one, questions of identity arise. In a society based on genetics, who is the real Jerome? The individual who passes through the turnstile every morning or the man whose DNA profile passes the turnstiles? And what happens to sexual relationships in such a society? In one scene, people queue up to have DNA samples analysed - single strands of hair from potential lovers and partners - including one woman who has her lips swabbed to analyse the DNA of the man she kissed 20 minutes earlier, to see if she should take the relationship any further. Another nice touch is the helical staircase in the apartment shared by Vincent/Jerome and Jerome/Eugene.

Genes are not destiny, but they could become so if everyone starts believing that they are. Anyone who thinks the mindset of the world of Gattaca a tad implausible should turn to the excellent little book, The DNA Mystique - the gene as a cultural icon by the American sociologists of science Dorothy Nelkin and Susan Lindee. For page after page after page, they catalogue the obsession that contemporary culture has with genes and DNA.

Gattaca is a modern morality play on the errors of genetic determinism. Equally we should avoid the trap of technological determinism - of thinking that such a stylish but oppressive future is inevitable. For the truth is that such consequences are dependent not only on the scientific research but also upon the public policy response of society. If we ordered society differently then we could have the benefits of gene discovery - freedom from the suffering imposed by genetic disease - without the demerits portrayed in this film.

Does making this society's problem absolve the geneticists of responsibility? It is unreasonable, in my view, to expect scientists whose expertise may be in, say, molecular biology also to have the expertise in the historical and social sciences necessary to form a judgement about the wider consequences of their research. Some may wish to express a view as concerned individual citizens; some may not.

But that is not the end of the matter. Next week, the Wellcome Trust will announce a programme to spend pounds 15m over the next five years examining the sorts of issues raised fictionally by Gattaca. Half the money will go on bringing such ethical issues to public attention. Two plays for secondary schools have already piloted the initiative: The Gift, on genetics; and Cracked on mental health.

The rest will go on research into the social and public policy consequences of biomedical advance, including understanding public attitudes and the values that inform public judgements on moral acceptability. The outputs of this research programme should help inform decision-makers at all levels about the appropriate policies to pursue in the light of developments in the laboratories and hospital clinics.

Most of the recent controversial scientific discoveries - Dolly for example - were the fruits of years of scientific research. Exploring their implications for society merits as serious an effort in social and policy research, rather than sound-bites and media punditry. That research may not lead to "the" answer, but it will map out some possible futures. Then it is up to society to decide.

And as for my genetic defect? That is a matter for me and my family. We do not live in the world of Gattaca. Yet.

Dr Tom Wilkie heads the biomedical ethics section at the Wellcome Trust.