A Technique for Sequencing DNA (1977)

Walter Gilbert and Allan M. Maxam devised a technique for sequencing DNA.

“The Gilbert-Maxam method involved multiplying, dividing, and carefully fragmenting DNA. A stretch of DNA would be multiplied a millionfold in bacteria. Each strand was radioactively labeled at one end. Nested into four groups, chemical reagents were applied to selectively cleave the DNA strand along its bases--adenine (A), guanine (G), cytosine (C) and thymine (T). Carefully dosed, the reagents would break the DNA into a large number of smaller fragments of varying length. In gel electrophoresis, as a function of DNA’s negative charge, the strands would separate according to length, revealing, via the terminal points of breakage, the position of each base.”