Q: How near are we to unlocking the secret code of life? A: Close. Very close

What, exactly, is being announced today?

What, exactly, is being announced today?

Scientists from two rival camps are formally publishing their respective analyses of the human genome, the genetic information locked up in the DNA code of the 23 pairs of human chromosomes. The genome controls how our bodies are built from a single fertilised egg cell, how they are kept alive, how they function normally, or abnormally, and even how they might eventually die.

Didn't they do this last year in the presence of Tony Blair and Bill Clinton when they said it was the most amazing feat since the invention of the wheel?

Not exactly. Last June the same scientists announced that they had completed the first draft of the genome, but this is the actual publication of that sequence of genetic letters spelling out the instructions in our genes. The new information has given us the first preliminary insight into what we can find on this map of the genome.

The map itself describes each of the 46 human chromosomes (23 pairs), which are made of DNA, the information molecule of life. It is the correct order or sequence of the 3 billion "letters" of the DNA code that the scientists have, more or less, completed today - more than 90 per cent of it in fact. Sequencing of the final 10 per cent is expected to be finished within two years.

What, then, is the most interesting thing that we have learnt?

All scientists involved are virtually unanimous in saying that the single most surprising fact to emerge from today's publications is that there are far fewer human genes than anyone had predicted. When the Human Genome Project was established, predictions of the numbers of human genes ranged from a minimum of 80,000 to as high as 140,000. But the real number is somewhere nearer to 30,000.

The privately funded team, led by Craig Venter of Celera Genomics in the US, has calculated that there are definitely 26,000 genes, plus another 12,000 "hypothetical" genes which its computers are still trying to validate. The publicly funded effort, which includes Britain's Sanger Centre in Cambridge, has calculated, by a different method, that there are between 30,000 and 40,000 genes. So the consensus is that the number of genes is about a third of what was originally expected.

Why should the number of human genes be so significant?

The humble fruit fly has 13,000 genes, the microscopic nematode worm has 18,000 and a tiny plant called the thale cress has 26,000, so there is clearly something other than the shear number of genes which makes humans so much more complex than simple lifeforms.

Dr Venter said that the finding is a body blow to the common fallacy that single genes determine all human traits, including those that are part of our individual personality, from alcoholism to homosexuality. "It says to me that we are not hardwired. The idea that there is a simple, deterministic explanation - that is: we are the sum total of our genes - makes me, as a scientist, want to laugh and cry," Dr Venter said.

The finding means that a set of instructions for making something as complicated as the human body and mind must have another component of complexity that scientists have yet to discover. It also emphasises that, whatever genes we are fortunate or unfortunate enough to inherit from our parents, it is the environment in which we are brought up, and how that upbringing and environment interacts with our genes, that is the real master of our destinies.

This cannot be the only new insight to be gleaned from today's announcement?

Far from it. The map published today shows that the human genome has vast stretches that are completely void of genes. These "deserts" are interspersed with "jungle" regions rich in genes. One chromosome in particular, chromosome 19, is unusually rich in genes, which scientists suggest is the result of some important and rapid stage of evolutionary development that took place early in our biological history.

Another finding is that the male Y chromosome, which men, but not women, inherit from their fathers, is actually one of the most desertified regions of the genome with hardly any genes that it can call its own. What genes it does have seem to have been copied from the female X chromosome. Being male, it seems, is not determined so much by the presence of a Y chromosome but by the absence of an extra X chromosome. As Dr Venter wryly put it: "Ladies will appreciate just how absolutely pathetic it is. There's just not much there."

All this might be interesting, but what are the real, practical implications of today's announcement?

These will not be immediately obvious, but the mapping of the human genome promises to revolutionise medicine over the coming decades. Defects in genes cause inherited disorders, such as Huntington's disease, and understanding the gene and its defect could lead to new treatments. Many other illnesses, such as heart disease, cancer and senile dementia, have a strong genetic component. Cancer, in particular, is now understood as a genetic disease, caused by something going wrong at the DNA level.

Knowing how genes contribute to ill health will enable scientist to design new drugs to target disease. All the medicinal drugs on the market at the moment are based on just 483 targets in the human body. Knowing how each of the 30,000 or so genes can go wrong opens a new vista on drug discovery and development.

The day will come when doctors will test your genes before giving you a drug tailor-made for your particular genetic type. It will be a move away from the "one size fits all" approach, said Francis Collins, one of the leaders of the publicly funded effort in the US.

He believes, for instance, that "genomic medicine" will revolutionise the way we treat the mentally ill. "We are certainly close to understanding the hereditary contributions to manic depressive illness, to schizophrenia and to obsessive compulsive disorder in a way that should at last lead to a better biological understanding of mental disorders," he said.

Some of the scientists in the publicly funded effort also believe that the new insights into the human genome will eventually provide important treatments for more obscure ailments, such as addiction to gambling, jet-lag and sleep disorders.

Where do we go from here?

Within the next two years, scientists should have completed sequencing the genome in its entirety. Although we are all more than 99.99 per cent identical in terms of our DNA, it is the tiny differences which may account for why one person succumbs to cancer or heart disease, while another thrives while being exposed to the same environmental risks. Knowing these differences, and how they exert their effects, will be crucial to a greater understanding of disease.

Are their any potential dangers from this research?

Yes, which is why a proportion of the human genome project's budget was spent on studying the ethical implications. Knowing our genes will tell us much about our evolutionary past and could allow us to control our evolutionary future. Within the next 30 years, science will almost certainly have found a safe way to engineer human genes at the level of sperm, egg and embryo. That could make "designer babies" a realistic possibility. It could mean genetic enhancement. It could mean a Brave New World. It could mean many things. It depends on what society decides to allow.

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