Linkage analysis is a recombinant technology used for gene mapping. If two genetic loci segregate together in a pedigree more often than by random chance, they are said to be linked, that is they lie close on the same chromosome. What makes the detection of linkage between two markers on a chromosome possible, are the recombination events which occurred during meiosis. Thus, information can be obtained for the location of a mutant gene by using markers with known locations. Since the first published reports of linkage over thirty years ago, the use of the "lod score" method to determine the chromosomal location of a disease gene has become widespread. With the continual production of new RFLPs, the mapping of new loci will continue to become faster and more efficient. The power of the linkage method has spawned the development of several new techniques which utilize marker data to graphically represent the most likely location of a disease gene. Such advances, however, can best be utilized only after initial chromosomal localization of the particular gene through the lod score method.