Molecular Physical Maps
The physical maps of DNA fragments, chromosome segments, whole chromosomes or whole genomes are based on physical distances. These physical distances are measured in terms of relative physical lengths or in terms of kilobase pairs between genes or molecular markers or in terms of relative distances of these genes/markers from the centromeres. For instance, the distance of a marker from the centromere may be expressed as a fraction of the length of the whole arm taken as unity, so that the distance of a marker from centromere will be indicated as 0.1, if its distance from the centromere measures one-tenth of the whole arm.
Physical maps may also obtained in the form of restriction maps, where for one or more enzymes, the restriction sites are shown to be separated by distances expressed in terms of kilobase pairs.


