The average human body contains around 100 trillion cells and within each of them is a tightly-coiled molecule which would stretch to around two metres in length if it was unravelled.
The structure of this molecule would resemble a ladder and, if it is scaled up to the size of one you'd find in many sheds around the country, it would stretch around half a million miles. That's all the way to the moon and back again!
The ladder has just over three billion rungs, which is one every twenty centimetres on our full size version, and it's these rungs that hold the key to life itself.
These rungs are scientifically known as 'base-pairs', and come in four colours. It is the sequence of these coloured rungs that make up the genes that literally build and operate the human organism.
Each of our 21,000 or so genes determines a specific feature or function in the body and is simply a series of base-pairs found at a specific location on the ladder.
Cracking the code
Each one of our genes contains an average of 27,000 base-pairs (although there can be an enormous variation on this) and the HGP set out to identify each of the three billion base-pairs and their locations, as well as the functions they form collectively.
The entire human genome was sequenced in April 2003, 13 years after research began. Most of the research was based on the DNA of a single male donor from Buffalo, New York, who was randomly selected from the wider donor group. However, not even he knows who he is, as he's simply known by the code name of RP11.
Over a decade on
The aim of the project over the long term is to develop a full understanding of the structure and function of the human genome, and be aware of its role in both disease and health. So how much do we understand 13 years after the human blueprint was put into use?
The honest answer is not quite as much as we had hoped, but more than you might think.
Following the publication of the human genome sequence in 2003, a wave of media and public speculation over the following years led to hopes that we would soon be able to eradicate disease and live long healthy lives, free of all ailments.
We were excited and our expectations were high (perhaps too high) but a decade later, the reality is that the scientific community is still processing the vast amount of data contained in the genome and applying it to clinical practice.
However, there have been some major advances. We now know that our genome contains far fewer genes than we had originally thought. We also know that what was previously considered to be 'junk DNA' (vast sequences of base-pairs found between genes) in reality plays a really important role in our biology.
The area that has become most interesting though is what is known as genomic medicine. This is the use of genomic sequences to optimise individual healthcare.
Genomic medicine: the future
There are two major applications for genomic medicine.
The first is in identifying our genetic susceptibility to developing specific diseases. The genes (or rather their variants) responsible for pre-disposing us to almost 2,000 medical conditions including breast cancer and Alzheimer's disease have already been identified. With sequencing technology becoming cheaper by the year, we can now, as individuals, have these genes cost effectively sequenced to find out if we are at high risk.
This means that we can then reduce that risk by engaging in preventive medical care more pro-actively and by ensuring that our lifestyles are positively adjusted.
The second focus is in the area of personalised medicine. This means tailoring the prescription of drugs to best effect, according to your personal genome. An example of this could be the use of a specific cancer drug, which may be far more effective for one patient and not as effective for another. The reason for this can put down to the genetic make-up of the two patients.
By understanding a patient's personal genome, clinicians can proactively target drug selection to ensure that the most effective medication is used from the outset, thereby increasing the chances of recovery and even survival.
The big question
The big question for the future of course is whether or not we'll one day be able to actually 'switch off' diseases. Gene therapy, where faulty, disease-inducing sequences of base pairs are altered or replaced, has been researched and trialled with increasing success in recent years for a wide range of conditions and will certainly play a major part in the future development of genomic medicine.
While there is still a long way to go before we can use the full potential of genomic medicine, we do know we're making major advances all the time. That can only be good news for the generations of the future.
Ten years is a relatively short space of time in medicine, especially given the vast scale of information provided by the HGP but, like Pandora's box, the consequences of cracking 'God's code' will stretch far into the future.