A Genome map may be defined as a detailed schematic description of the structural and functional organisation of all the chromosomes in the genome of an organism. At present we have mainly two types of maps (1) Genetic or linkage maps and (2) Physical Maps. A genetic map is prepared on the basis of recombination data between carefully selected genetic Markers usually ordered into suitable crosses but in case of humans linkage maps have to the prepared using family pedigree data in addition genes could be assigned to a specific chromosome arms using somatic cell hybridization Linkage groups have been assigned to specific chromosomes in the genome by using appropriate cytogenic techniques in conjunction with linkage studies. The chief problem of linkage mapping is the non availibility of a sufficient number of genetic markers to cover the entire genome.
Therefore, search for more abundant markers continued and resulted in various molecular markers, e.g. RFLP, RAPD and STR used in mapping of chromosomes. Chromosome maps depieting the location of these molecular markers, whose genetic function is ordinarily not known, are called physical maps.
In several species genetic maps have been being integrated with the physical maps to yield a highly useful genomic map using which genes of interest can be detected and or isolated with the help of more convenient and highly reliable molecular markers such studies have revealed that in human I centimorgan the distance which allow 1% recombination between two markers represents about 1000 kb of DNA while in mice it is equivalent to about 1600 kb DNA.