In the few years since its introduction[84, 85, 86], the polymerase chain reaction has become a widespread research technique. This popularity of the PCR is primarily due to its apparent simplicity and high probability of success. In fact, the PCR is a relatively complicated and, as yet, incompletely understood biochemical brew; where constantly changing kinetic interactions among the several components determine the quality of the products obtained. Although good results will be obtained in most cases, there are a number of parameters that can be explored if better results are required or if the reaction fails altogether.
Because of the great variety of applications in which PCR is used, it
is probably impossible to describe a single set of conditions that will
guarantee success in all situations. Nevertheless, the reaction outlined below
proved to be adequate for most amplifications and in those cases where
problems are encountered, it provides at least a starting point from which modifications can be
attempted (e.g., the Mg 
concentration should be checked in every new
PCR setup).
The standard PCR is typically done in a 50 
l volume and, in addition to
the sample DNA, contains 50mM KCl, 10mM Tris 
HCl (pH 8.4), 1.5mM
MgCl 
, 100 g/ml gelatin, 0.25 M of each primer, 200 M of each
deoxynucleotide triphosphate (dATP, dCTP, dGTP, and dTTP), and 2.5 units of
Taq polymerase .
The type of the DNA sample will be variable, but it
will usually have between 10 
and 10 
copies of template (e.g., 0.1
g human genomic DNA).