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In the past, geneticists have looked at so-called disease genes, but a lot of people have changes in their genes and don't get these diseases. There have to be other parts of physiology and genetics that compensate.

Many people assume the diseases that kill us are pre-programmed into our genes. High blood pressure by 55, heart attacks at 60, maybe cancer at 70, and so on... But for most of the leading causes of death, our genes usually account for only 10-20 per cent of risk.

First of all, many human diseases are influenced by, if not caused by mutations in genes.

Once we all have our genomes, some of these extremely rare diseases are going to be totally predictable.

A person's health isn't generally a reflection of genes, but how their environment is influencing them. Genes are the direct cause of less than 1pc of diseases: 99pc is how we respond to the world.

Genes work with probabilities; they don't work with certainties. So most things that you're looking at with these genetic tests, it's not like you're condemned to automatically get the disease or the syndrome. There's a lot of factors in play there.

All human beings are, in fact, born with dozens of mutations their parents lacked, and a few of those mutations could well be lethal if we didn't have two copies of every gene, so one can pick up the slack if the other malfunctions.

There are some people who're all doctors. Is it genetic?

DNA sequencing opens vast ethical issues. We shall be able to know who has defective genes. What will it mean when we can be sure we're not all born equal? Worked out, the implications will scare a lot of people. Insurance companies will not want to cover those with a genetic predisposition to illness, for example. Here lurk myriad lawsuits.

If genetic research doesn't seemed to have lived up to its therapeutic promise, it's because sequencing is just too slow and expensive.