Applications of DNA biotechnology vary depending on the goals of firms, pharmaceutical companies, and forensic scientists. In forensic DNA analysis, a very common tool is the polymerase chain reaction (PCR) used to make billions of copies of selected pieces of DNA. It involves two major steps: (1) synthesizing short pieces of DNA, called primers, that identify the DNA segment to be copied, and (2) running repetitive reactions to make multiple copies of the DNA. To start with, forensic scientists collect DNA samples such as blood from a crime scene. The target DNA is then mixed with primers, free nucleotides, and an enzyme called DNA polymerase in a small test tube. The mixture is then cycled through a series of temperature changes, doubling the amount of DNA with every cycle. Following PCR, the now amplified DNA sample is subjected to restriction enzymes, enzymes that cut DNA at specific locations. The mixture of DNA fragments is then separated by a technique called gel electrophoresis, where DNA fragments are separated by size, forming distinct bands on the gel. By the end of the process, a DNA profile is established and suspects can be identified.