These enzymes recognize short sequences of DNA and cut them at specific sites. Since scientists have characterized hundreds of different restriction enzymes, DNA can be cut into many different fragments. Different types of physical maps exist. To sequence DNA, it must be first be amplified, or increased in quantity. Cloning involves the propagation of DNA fragments in a foreign host.
Vectors normally used are viruses, bacteria, and yeast cells.
With PCRs, DNA can be amplified hundreds of millions of times in a matter of hours, a task that would have taken days with recombinant DNA technology. PCR is a process through which a specialized polymerase enzyme synthesizes a complementary strand of DNA to a separate given strand of DNA in a mixture of DNA bases and DNA fragments. The mixture is heated, separating the two strands in a double-stranded DNA molecule. The mixture is then cooled and through the action of the polymerase enzyme, the DNA fragments in the mixture find and bind to their complementary sequences on the now separated strands. The result is two double helix strands from one double helix strand.