There are three billion letters in the DNA code in every one of the 100 trillion cells in the human body
The four letters of the DNA alphabet (A, C, G and T) carry the instructions for making all organisms, with each set of three letters corresponding to a single amino acid
There are 20 different building blocks (amino acids) used in an array of combinations to produce proteins as different as keratin in hair and haemoglobin in blood
The vast majority (97 per cent) of the DNA in the human genome has no known function
Between humans, DNA differs by only 0.2 per cent (1 in 500 letters), which takes into account that human cells have two copies of the genome
Human DNA is 98 per cent identical to that of chimpanzees
Estimated number of genes: humans and mice (60,000 to 100,000); round worm (around 19,000); yeast (around 6,000); the microbe responsible for tuberculosis (around 4,000).
