A physical map of a chromosome or a genome that shows the physical locations of genes and other DNA sequences of interest. Physical maps are used to help scientists identify and isolate genes by positional cloning.


Physical maps of DNA reflect the location of landmarks across a chromosome. Such landmarks can correspond to functional parts of the DNA, such as genes, or just random non-functional sequences. At a minimum, physical maps depict the relative order of landmarks across a chromosome; more refined physical maps actually indicate the exact distances between adjacent landmarks. Nowadays, very precise physical maps can be constructed based on the actual sequence of a chromosome, which provides exact base pair distances between landmarks.

- Eric D. Green, M.D., Ph.D.