The single strand conformation polymorphism (SSCP) technique is based on the electrophoretic behaviour of a single-stranded DNA fragment in a non­ denaturing acrylamide gel. In fact, a molecule of single-stranded nucleic acid may form secondary structures due to pairing of bases within the molecules. These secondary structures depend on the sequence proper to the DNA strand and give a particular conformation to each type of single strand molecule. Thus, two sequences of DNA that are very similar can be differentiated on the basis of the conformation of their single-stranded form. Two alleles of a single gene will be distinguished. This makes it possible, for example, to detect a mutant allele (possibly responsible for a genetic disorder) in an individual. This simple technique has two major disadvantages: the electrophoretic behaviour of single-stranded molecules is unpredictable because it is closely dependent on the temperature and conditions of electrophoresis and, for large fragments (> 200 bp), all the mutations do not seem to be detectable (the method can be used to detect essentially sequence variations of micro-insertion or micro-deletion type).