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DNA Testing - Five Things To Know

Perhaps the most exciting frontier in the field of criminal justice, DNA testing has grown by leaps and bounds over the past couple decades. It has gone from being a fringe science to an integral part of any major investigation and some minor ones as well.

If you have been charged with a crime, you should know the truth about how DNA testing is actually used. While its portrayal in the popular imagination through shows like Law and Order or CSI might be over the top, DNA testing is still an important element of any criminal investigation. Be sure to discuss the implications of a potential DNA test with your criminal defense attorney before your trial.

What You Should Know

  1. DNA can be retrieved from just a few cells of sweat, skin, hair, blood, saliva, semen, or any other bodily fluids. Identifiable DNA can remain at a crime scene for months following the act. Unless they've been extremely careful, most people leave at least a bit of themselves behind at a crime scene.
  2. DNA testing can more easily prove innocence than guilt. When matching a DNA fingerprint to a sample, all of over ten elements must be equal. Any unequal elements means that there's definitively no match between the samples. Furthermore, a match is not always 100% accurate. It is just one more piece of evidence.
  3. There are two types of DNA testing. RFLP, or Restriction Fragment Length Polymorphism, is commonly known as DNA fingerprinting. PCR, or Polymerase Chain Reaction, is commonly known as an amplification test.
    • RFLP takes up to eight weeks, requires a better sample but has an accuracy rate of one in three billion.
    • PCR takes one to three days, can be conducted on minimal sample but has a 1-10 percent of providing a false positive.

  4. A national database of DNA profiles, known as CODIS (COmbined DNA Index System), has been compiled from information held by local, state and federal authorities. It is now common practice in many jurisdictions for arrested individuals to be both fingerprinted and sampled for DNA.
  5. One key block to the efficiency of DNA testing is the huge backlog of tests waiting to be done. There are not enough resources, machines or personnel to be able to handle all the needed DNA tests. While DNA tests may provide information for minor cases, generally only major cases have immediate access to DNA testing equipment.