<prompt> For PCR which of the following is not required:Taq polymerased-NTPPrimerRadiolabelled DNA probe  <response>: Radiolabelled DNA probe Polymerase Chain ReactionPCR is a cell-free, test tube method for amplifying a target sequence of DNA. It is much faster and more sensitive than cell-based cloning.Materials required:Two primers, each about 20-35 bases long with sequence complementary to the sequence immediately adjacent to the DNA segment of interest flanking sequence . DNA polymerase e.g., Taq polymerase which can sustain high temperature 600 C. A large number of free deoxynucleotides dNTPsThe target DNA fragment.Procedure:There are three major steps in a PCR, which are repeated for 20 or 30 cycles.a. Heat Denaturation- The DNA sample to be amplified is first heated to separate the two strandsb.Annealing- The primers bind to the two separated strands of DNA one for each strand flanking the target sequence.c.Extension- Each strand is copied by the DNA polymerase, staing at the primer site. The two DNA strands each serve as a template for the synthesis of new DNA from the two primers.The above three steps are repeated again and again . The number of copies doubles in each cycle. Typically 20-30 cycles are run during this process. There is an exponential increase in the amount of target DNA, amplifying it by a million-fold to a billion-fold.By using a heat stable DNA polymerase Taq polymerase , the polymerase is not denatured and, therefore does not have to be added at each successive cycle.Advantages:The major advantage of PCR over cloning as a mechanism for amplifying a specific DNA sequence aresensitivity : DNA sequences present in only trace amounts can be amplified to become the predominant sequencespeedless technically difficult than traditional cloning methods using recombinant DNA techniques. Disadvantages:To synthesize primers, we need to know the sequence flanking the DNA segment of interest.Applies only to sho DNA fragments, typically less than 10 kb. 