DNA sequencing of the human genome: computer display of an automated method of decoding the sequence of base-pairs in fragments of DNA extracted from human chromosomes. Mapping & sequencing are two phases of the human genome project, an ambitious plan to reveal all of the information encoded in the 23 pairs of human chromosomes. Mapping refers to a physical survey of each chromosome to determine the exact location of genes or other genetic markers. Sequencing of all the DNA in the human genome would involve manipulating 3 billion base-pairs. Photographed in Leroy Hood's laboratory at CalTech, USA.