The four bases - adenine (A), guanine (G), thymine (T), and cytosine (C) - spell out the genes.

BBC: DNA pioneer is honoured

Most important, they can't read the 3 billion letters--A, C, T and G, for the nucleotides adenine, cytosine, thymine and guanine--in the human genome from beginning to end, the way one reads a book.

FORBES: Magazine Article

Embedded in each set of 23 chromosomes are 3 billion base pairs of DNA, known by the letters A, T, C and G, for the chemical bases adenine, thymine, cytosine and guanine.

FORBES: On The Cover/Top Stories