The double helix structure of human DNA (deoxyribonucleic acid) was discovered by James Watson and Francis Crick in 1953.
* DNA is made up of sugars, phosphates, and four molecules called bases - adenine, guanine, thymine and cytosine, usually known as A, G, T and C.
* DNA is full of "codes", comprising strings of these letters in threes, for example AAA or TAC. The technical name for the strings is nucleotides.
* These codes tells every cell in the human body what to be and what to do.
* Each human being has about three billion bits of information in his or her DNA codes.
* Some codes control the 80,000 or so genes each person inherits. There are many more codes, with unknown functions, that scientists call "junk".
* Mapping the human genome involves identifying the entire code and putting all the letters in the right place - thus creating a blueprint for a human being.