The gene instructions of any two people differ by about one DNA base pair in every thousand, or 0.1 per cent of the entire manual. So who will provide the 'definitive human genome'? In fact, Human Genome Project scientists are basing most of their studies on DNA from six different individuals. This will still provide a 'reference manual' that will be over 99 per cent accurate for everyone. Other scientists are looking for all the different versions of every human gene, to uncover the many variations.