Research on the human genome: Caltech scientist Leroy Hood preparing an electrophoresis gel used in a computer-controlled system for DNA sequencing of human chromosomes. DNA sequencing involves decoding the base-pair sequence of sections of DNA encode specific proteins. Sequencing and mapping - surveying each of the 23 pairs of human chromosomes to locate genes or other important markers - are two phases in the human genome project. The human genome is a complete genetic blueprint" - a detailed plan of every gene expressed on all 23 pairs of chromosomes."