It is essential to denature the template DNA completely. Initial heating of the PCR mixture for 2 minutes at +94 to +95°C is enough to completely denature complex genomic DNA so that the primers can anneal to the template as the reaction mix is cooled. If the template DNA is only partially denatured, it will tend to "snap-back" very quickly, preventing efficient primer annealing and extension, or leading to "self-priming", which can lead to false-positive results