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The development of genetic maps for an organism can be traced back to the first genetic experiments of Sturtevant. The discovery that loci can be placed into ordered arrangements, based on the observation of recombination events, has led to the development of genetic linkage maps for a number of plant and animal species. The only requirements are the availability of distinguishable alleles at a locus and the abilities to perform genetic crosses and to analyze the resulting progeny. Among plant species, maize (Zea mays L.) has one of the best developed genetic linkage maps available. The species has a long history of genetic investigations, due in part to the ease with which it can be manipulated genetically and to its important role as a major agronomic crop species. The current genetic database contains nearly 600 unit factors, of which nearly 400 have sufficient linkage information available to place the locus to a specific genetic position on the linkage map. These factors include loci defined by morphological variations (conventional loci) and by biochemical variants (isozymes and protein polymorphisms). In addition, there are the nearly 900 loci defined by DNA polymorphisms (Restriction Fragment Length Polymorphisms, RFLPs). |
