The Gene Dilemma: Who are you - the perilous knowledge: In the first of a three part series Independent writers report on the cutting edge of research into human genes

A MILLION people in Britain are members of families affected by genetic disorders and 15,000 babies are born each year with significant inherited disabilities.

One in three Britons will suffer cancer - a disease influenced by defective genes, although it is seldom inherited. Many will die of Alzheimer's and heart disease, both also thought to have a genetic component.

Dramatic advances in genetics over recent years now offer the prospect of diagnosing and treating today's most incurable diseases.

As the new year dawned, French scientists announced that they had discovered genes linked to human ageing. It was the latest instalment in a stream of genetic knowledge which is pouring out of the world's research laboratories. And the pace will quicken.

The French researchers themselves fear for the consequences of their own discovery - that it may tempt insurance companies to test their prospective clients to ascertain not only what they are likely to die of, but when they are likely to die.

Others fear that the scientists may be trampling on the very stuff of humanity and that the door may have been opened to a Brave New World - where parents might selectively abort their unborn children until they obtain one with the genetic profile indicating high intelligence; where other children might grow up with their lives blighted by the foreknowledge that they are genetically predisposed to an early death; and where adults might try to alter the natural order of things to postpone or cheat their inevitable demise.

Parents wanting healthy children will benefit, but who is to define 'bad' and 'good' genes? Most people would agree that a crippling genetic disorder is bad, but what about genes influencing sexual preference? Last year researchers identified an inherited component to homosexuality that could result in the discovery of a 'gay gene'.

What pressure will scientists come under to identify 'good' genes in the hope that society could improve longevity, height or even intelligence? True designer babies would then be a possibility.

In the developed countries, genetic and congenital disorders have emerged as the single biggest killer of children now that the battle against the infectious scourges of the past has been won. A third of paediatric admissions to UK hospitals are now the result of inherited disorders.

Gene technology that came of age in the 1980s will change fundamentally the way doctors treat patients. It holds out the prospect of diagnosing disease before it strikes and of eliminating it by gene therapy - replacement of defective genes with healthy substitutes.

In a few years it might be possible to produce genetic read-outs on patients that list the inherited traits they could suffer from later, such as heart disease and cancer.

Scientists are well on the way to finding the location of each of the estimated 100,000 genes on the 46 human chromosomes - the genome. Finding a gene quickly leads to the development of a genetic test and a better understanding of an inherited disorder. Hunting down and mapping the position of every human gene is a huge undertaking. The dollars 3bn ( pounds 2.02bn) international Human Genome Project has been likened in scale to President John F Kennedy's declared mission in 1961 to send a man to the Moon.

The genes are made of DNA - the genetic blueprint - which is the largest molecule known. If all the DNA in the 46 chromosomes of one human cell were stretched end to end it would measure 2 metres. All the DNA in the human body, stretched end to end, would reach to the Moon and back 8,000 times.

Scientists have discovered that the estimated 100,000 human genes reside in just a small fraction, perhaps 10 per cent or less, of the DNA molecule. Pinpointing the position of each gene could be compared with searching for a burnt-out light bulb in a house without knowing the address.

And yet barely a week goes past without an announcement of another gene discovery. In 1973, scientists had located just 25 genes. By 1989 this had grown to 1,656. By the end of 1991, the figure had reached well over 2,100. Within the first decade of the next century, scientists on the Human Genome Project predict they will have mapped all 100,000 or so human genes.

James Watson, the co-discoverer in 1953 of the DNA double helix structure, a find that helped to spawn the new genetics, said the implications of mapping the entire human genome will be greater than landing a man on the Moon: 'A more important set of instruction books will never be found by human beings. When finally interpreted, the genetic messages encoded within our DNA molecules will provide the ultimate answers to the chemical underpinnings of human existence.'

Scientists have described more than 5,000 inherited disorders caused by single gene defects.

Unravelling the message of the human genome holds out the prospect of treating what have been stubbornly incurable illnesses.

But it does much more. It allows humanity to delve into a hidden genetic resource that has taken millions of years to evolve. It poses questions that have yet to be widely debated in the public arena, such as: Who has the right to know what is written in someone's genes? Who has the right to own genetic information? Who has the right to act on genetic information?

The debate must begin sooner, rather than later.

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