One of the most surprising findings of modern genomics has been the discovery that our genomes are infinitely more versatile and complicated than we had envisioned before the human genome sequence was complete.

Scientists had estimated that humans had around 100 000 genes, each with a specific function - to make a specific protein. We now know that humans have a mere 22 000 genes - but that each of these probably has many different roles. Each gene is likely to code for different proteins in different tissues and at different points in our development. 

As the complex nature of our genes emerges, researchers are increasingly focusing on the areas of the genome outside the actual 'coding' regions (our genes) for clues as to how our DNA makes us what we are. These areas are not genes themselves, but they regulate gene activity, determining when and whether a gene is switched 'on' (generating proteins) or 'off' (inactive). It is subtle differences in the timing of gene action in the womb and over our lifetimes that appear to make humans distinct both from other organisms and from each other - crucially even from an identical twin.