Frederick Sanger, at the Medical Research Council Laboratory of Molecular Biology in Cambridge, develops in 1977 the dideoxy method — known as the Sanger method — for determining the exact base sequence of a DNA molecule. The technique uses modified nucleotides (dideoxynucleotides) that, when incorporated during the synthesis of a new DNA strand in the laboratory, abruptly halt the process at a known point, generating fragments of different lengths that, analyzed by gel electrophoresis, allow the complete sequence to be read letter by letter. Walter Gilbert, at Harvard University, independently and almost simultaneously develops an alternative method based on selective chemical degradation of DNA, less used in practice than Sanger's method but equally valid conceptually. The Sanger method becomes the standard DNA sequencing technique for more than two decades, used — with progressive automation via capillary sequencers — to complete the Human Genome Project in 2003. Sanger also applies his own method in 1977 to sequence the complete genome of bacteriophage φX174, the first complete genome of an organism ever sequenced in history.