The process used to obtain the sequential arrangement of nucleotides in the DNA backbone. The cleavage into fragments (followed by separation of those fragments, which can then be sequenced individually) of DNA molecules by one of several methods: (1) a chemical cleavage method followed by polyacrylamide gel electrophoresis (PAGE), (2) a method consisting ofcontrolled interruption of enzymatic replication methods followed by PAGE, (3) a didexyl method utilizing fluorescent “tag” atoms attached to the DNA fragments, followed by use of spectrophotometry to identify the respective DNA fragments by their differing “tags” (which fluoresce at different wavelengths). This (fluorescent tag) variant of the dideoxy method can be automated to “decipher” large DNA molecules (i.e., genomes). Such automated machines are sometimes called “gene machines.”