A sample of DNA is taken from blood of saliva. PCR makes lots of copies, or amplifies the DNA. We then add restriction enzymes to cut the DNA at palindrome sequences. We then run the DNA through gel Elecrophoresis. Each person has unique short tandem repeats that cause a unique number of cuts by the restriction enzyme. These cuts are separated by size on gel electrophoresis, so no two people have the exact same pattern. We can compare individuals banding patterns to what is found at a crime scene, taken in previous samples, in a baby, and the sample that matches all the banding patterns will be the individual.
