What controls which dna is amplified in pcr?

Primers

Explanation:

PCR or Polymerase Chain Reaction is in vitro techinque, widely used for production of DNA copies of a specific DNA region. The major components of this reaction are thermostable enzyme Taq polymerase and primers designed for specif region of DNA that is region of interest.

PCR reaction is repeatedly cycled through a series of temperature changes, and the purpose of it is to make as much amplified DNA sequences for further investigations.