The DNA Variation of Interest to Forensic Scientists

The regions of DNA that forensic scientists use to individualize people contain repeated sequences. There are different types of repeat-sequence DNA. A repeated sequence may be found in many different places in the genome. These can be called “interspersed” sequences. Some repeated sequences are head-to-tail repeats of a sequence altogether at one location within the DNA. These are sometimes called “tandem” repeats, and they are the ones that forensic scientists use.

In the context of these regions of DNA the variation between people consists of the number of repeats at a tandem-repeat location. One person might have 10 repeats, and someone else might have 12 or 14 or some other number. The physical structures that contains the DNA are the chromosomes, and humans have 46 chromosomes, which are grouped into 23 pairs. One member of each pair is inherited from one’s mother, and the other comes from one’s father. Thus, everyone has a pair of these tandem-repeat regions. And there may be a different number of repeats on one chromosome compared with the other. Analyzing a person’s DNA for several different DNA locations that have tandem repeats can reveal the high degree of individuality that it represents.