Use of DNA in Criminal Investigations

Before the 1980s, courts relied on testimony and eyewitness accounts as a main source of evidence. Notoriously unreliable, these techniques have since faded away to the stunning reliability of DNA forensics. In 1984, British geneticist Alec Jeffreys of the University of Leicester discovered an interesting new marker in the human genome. Most DNA information is the same in every human, but the junk code between genes is unique to every person. Junk DNA used for investigative purposes can be found in blood, saliva, perspiration, sexual fluid, skin tissue, bone marrow, dental pulp, and hair follicles (Butler, 2011). By analyzing this junk code, Jeffreys found certain sequences of 10 to 100 base pairs repeated multiple times. These tandem repeats are also the same for all people, but the number of repetitions is highly variable. Before this discovery, a drop of blood at a crime scene could only reveal a person’s blood type, plus a few proteins unique to certain people. Now DNA forensics can expose a person’s gender, race, susceptibility to diseases, and even propensity for high aggression or drug abuse (Butler, 2011). More importantly, the certainty of DNA evidence is extremely powerful in court. Astounded at this technology’s almost perfect accuracy, the FBI changed the name of its Serology Unit to the DNA Analysis Unit in 1988 when they began accepting requests for DNA comparisons (Using DNA to Solve Crimes, 2014).

There are thirteen standard tandem repeats used in modern forensics, and together these sequences create a DNA profile. Except in the case of identical twins, the probability that two people have the same genetic code at all thirteen core loci is less than one in one trillion (Jones, 2004). Investigators compare these...

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H.M. Wallace, A.R. Jacksona, J. Gruberb, A.D. Thibedeaub. Forensic DNA databases–Ethical and legal standards, ScienceDirec, 2014.

Westphal, Sylvia Pagán. DNA profiles link dope to its source. Daily News, 2003

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