Restriction fragment length polymorphisms (RFLP) are based on the hybridization of DNA probes to fragments of DNA produced by cutting with specific restriction endonucleases and size fractionated by electrophoresis. RFLPs (Figure 13.2) are used to detect variation in nucleotide sequence among homologous sections of chromosomes due to restriction-enzyme recognition-site changes along the section of chromosome where the probe hybridizes. Because RFLPs can detect variation in both coding and noncoding regions of DNA, they are much more variable than isozymes and therefore more useful markers (Figure 13.3). RFLP and isozyme methods have been commonly used to analyze populations and to recognize subdivisions within these populations (Table 13.3). The RFLP technique is a convenient method to study long-range dispersal patterns of plant pathogenic fungi and suggested the airborne dispersal of the wheat stem rust fungus from India and Africa to Australia across the Indian Ocean.

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