PCR stands for polymerase chain reaction and is a method for amplifying DNA. Using PCR, millions of copies of a DNA sequence can be generated from a single copy or just a few copies of DNA. PCR was developed by Kary Mullis in 1983. PCR protocols consist of assembling a PCR reaction mix containing Taq polymerase (a thermostable DNA polymerase that can withstand the high temperatures required for thermal cycling), primers (short DNA sequences that define the target region for amplification), deoxynucleotide triphosphates (dNTPs, the building blocks of DNA) and MgCl2 (Taq polymerase co-factor) in a buffered solution. The reaction mixture undergoes three basic thermal cycling steps including (1) denaturation (usually at 95°C, (2) annealing (usually lowest primer melting temperature - 5°C, (3) extension (usually at 72°C).