How did scientists read genes?
Your genes are made of DNA: a chemical code with four 'letters', known as bases, arranged in pairs. The complete human instruction manual, known as the human genome, is made of three billion DNA base pairs. Only around 3% of them spell out genes. Scientists are still trying to decipher what the remaining 97% of your DNA does. The aim of the Human Genome Project was to read the complete manual, i.e. to sequence the entire genome.