Discontinuous Polyacrylamide Gel Electrophoresis of DNA Fragments

At present, the most polymorphic genetic markers are DNA regions composed of a variable number of tandem repeats (VNTRs) (1 ,2 ). The detection of VNTRs is made possible by restriction fragment-length polymorphism (RFLP) analysis via Southern blotting (3 ). The length of each DNA fragment is a function of the number of tandem repeats contained within it. The RFLP technique requires at least 10–50 ng of essentially undegraded DNA (10,000–20,000 bp) and isotopic detection to obtain a result; the time required for analysis may be in excess of one week (4 ).