A computer illustration of the double-helix structure of DNA, which carries the instructions for all living things.

A computer illustration of the double-helix structure of DNA, which carries the instructions for all living things.

By FRANCESCA MOLD

A breakthrough in mapping 97 per cent of the human genetic code is already being compared to scientific accomplishments like the development of penicillin and the moon landing.

It will give doctors new insight into the causes of diseases, and increase the chance of finding cures.

What is the human genome?

It is like a genetic blueprint which whittles down the human body to a complex string of letters, giving us information about how people develop - why they are tall, thin, blond or have brown eyes.

Basically, researchers have found a way to record page after page of the letters A, T, C and G, laid out in the order they appear on the body's chromosomes.

These letters stand for adenine, thymine, cytosine and guanine - nucleotides that sit, two by two, as the "rungs" of the twisted ladder that makes up DNA.

DNA is the chemical inside the nucleus of a cell that carries instructions for making living things and is contained within 23 pairs of chromosomes.

Each three pairs of nucleotides in the DNA control production of an amino acid, which in turn creates proteins, which make up cells, hormones and everything else in the body.

How will the discovery help people?

Having a full map of the human genome will help scientists locate disease-linked genes they would never have found. They will be able to figure out if we have the kind of prostate cancer that will kill, whether our type of leukaemia will respond to one drug or another. They will eventually be able to analyse genes to rank our chances of succumbing to heart disease or Alzheimer's.

Scientists will learn which genes turn on when a wound heals, when a baby's fingers grow, when a scalp becomes bald. And they will learn to manipulate those genes.

Knowing the genetic code will help with early diagnosis and treatment of people at risk from certain diseases.

Using the genome, scientists will be able to identify "faulty" genes and replace them.

For instance, eye experts can "replace" faulty genes by inserting a virus carrying a normal gene into the retina. The virus kills the faulty gene, replacing it with the normal one.

What could it tell us about our origins?