There are a number of factors that can affect the specifity of the
amplification reaction. The stringency of the annealing step can be controlled
to some extent by adjusting the annealing temperature. Minimizing the
incubation time during the annealing and extension steps will limit the
opportunities for mispriming and extension by molecules of otherwise idle DNA
polymerase. Reducing primer and enzyme concentrations also serves to limit
mispriming, particulary the type that leads to dimerization . Finally, changing MgCl 
levels can further improve specificity,
either by increasing the stringency of the reaction or by direct effects on the
polymerase itself (activity, processitivity, etc.).