They do this by extracting some DNA from the animal and testing it to see if it has a given chemokine gene. First, a researcher removes a tiny bit of skin. The DNA is then run through a process called a polymerase chain reaction. In the PCR process, the double-stranded DNA is heated just enough so that it opens up and can be copied. Researchers can regulate which sections of the DNA will be copied.
Electricity is run through the gel in order to exert pressure on the DNA molecules.
Smaller pieces of DNA move faster and so travel farther than the heavier ones. Once the gel has run for several minutes a fluorescent chemical called ethidium bromide, or EtBr, is added. EtBr mixes with the DNA and shows the DNA s position when viewed under ultraviolet light.