DNA is usually analyzed is short sequences know as Short Tandem Repeat sequences. STR analysis is usually carried out on nuclear DNA, or the DNA found in the cell nucleus. Essentially, it is short repeated DNA sequences that are analyzed. Repeated sequences consist of base pairs, which on DNA are basically four: adenine, guanine, cytosine, and thymine. Adenine might pair with thymine in a repeated sequence of ATATAT and this would be taken under scientific analysis in a DNA test. Scientists are able to discriminate between different DNA profiles using such repeats as the same regions located on the DNA profiles may differ from person to person. To analyze the DNA, the DNA must be amplified using what is known as polymerase chain reaction and then the scientist can go on to analyze the repeats.