The PCR Process 

The following is a basic overview of the PCR process:

• DNA samples extracted from the specimen are denatured, or split into two separate strands. (DNA naturally forms a two-stranded, "double-helix" shape.)

• Next comes annealing, where primers—short, synthetic sequences of single-stranded DNA (such as primers in the Roche AMPLICOR Test)—are used to mark off the selected segment of DNA sequence to be studied.

• Once the primers anneal to the DNA sequences, the temperature is raised to approximately 72°C. Taq DNA polymerase is used to copy, or replicate, the DNA strands in a process called extension. This process takes place in a thermal cycler, an instrument that automatically controls and alternates the temperatures for programmed periods of time for the appropriate number of PCR cycles (usually between 30 and 40 cycles). Each cycle doubles the amount of replicated DNA.