Fluorescence micrograph of human chromosomes showing the mapping of cloned fragments of DNA (DNA probes) on chromosome 6. The chromosomes are stained to give red fluorescence, with the DNA probes represented by regions of green/yellow fluorescence. Mapping chromosomes may be regarded as a physical survey of each chromosome to find the location of genes or other markers. Mapping & sequencing (decoding the base-pair sequence of all the DNA in each chromosome) are the two main phases of the human genome project, an ambitious plan to reveal all of the genetic information encoded by every human chromosome. Magnification: x12,500 at 35mm size.