Genetic and Physical Maps

In a genetic map markers are arranged in specific order determined by the frequency of crossing over between them the distance between neighbouring genes is represented in terms of centimorgans. In contrast a physical map deplets only the physical locations of markers the order and the location of various markers ids determined by using physical methods like in situ hybridization RFLP etc. Therefore when a known gene is located in a map by means of in situ hybridization it becomes a part of a physical map mere location of a gene or genes does not make th e map genetic map. To qualify as a genetic map, genetic methods must be used for preparing the map such a map must be prepared by using recombination data. Hence, when molecular markers e.g. RFLP, microsatelites probes etc, are pklace a map using recombination data a genetic map is generated. The physical and genetic maps can be integrated by studying recombination frequencies between the linked marker in appropriate segregating population e.g backcrosses etc. or in random sample inbreds derived from appropriate heterozygotes for the markers in question in case of human beings, this is done by studying the inhertance patterns of the selected markers in group of families choosen for the purpose. Initially, the human genome project selected a group of 59 families for the preparation of primary genetic linkage maps. These families represented from 1,212 meioses. In order to establish a permanent source of DNA, cel lines were established from the individuals of this group of selected families at the Centre for study of Human polymorphism, paris