First, DNA from an evidentiary sample must be isolated from that sample, and eventually, DNA must be collected from an individual who is a suspect in the case in question. DNA is extracted from the crime scene or person, and then the size of the DNA sample is determined. As mentioned earlier, DNA is made up of A, T, G, and C. At some point, letters tend to repeat themselves. This set of letters is known as variable number of tandem repeats (VNTR). Short tandem repeats (STRs) are similar to VNTRs. VNTR sequences (10 to 100 base pairs) are much longer than STR sequences (2 to 9 base pairs). STRs are more useful because they can be amplified by PCRs, giving scientists more to work with when they have a small sample of DNA. Any biological DNA stored dry or frozen can also be used as a sample. Second, the DNA must be processed so that test results can be generated. Once the STRs are detected, the number of repeats in the DNA sequence is determined, which is called genotyping the sample. Finally, the results are compared to determine whether or not the sample matches that of the sample.