Among the notable of the inventions from Hood's lab was the automated DNA sequencer. It made possible high-speed sequencing of the structure of DNA, including the human genome. It automated many of the tasks that researchers had previously done by hand. Researchers Jane Z. Sanders and Lloyd M. Smith developed a way to color code the basic nucleotide units of DNA with fluorescent tags, green for adenine (A), yellow-green for guanine (G), orange for cytosine (C) and red for thymine (T). Four differently colored fluorophores, each one specific to a reaction with one of the bases, are covalently attached to the oligonucleotide primer for the enzymatic DNA sequence analysis. During the analysis, fragments are passed downwards through a gel tube, the smallest and lightest fragments passing through the gel tube first. A laser light passed through a filter wheel causes the bases to fluoresce. The resulting fluorescent colors are detected by a photomultiplier and recorded by a computer. The first DNA fragment to be sequenced was a common cloning vector, M13.