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All in the genes;Fact file;DNA;Cutting Edge

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.

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