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DNA Testing - Five Things to Know

Jun 16th 2014 at 12:52 AM

Perhaps the most thrilling element in the field of criminal justice, DNA testing has advanced by leaps and bounds over the past few decades. From being a seldom used fringe science, DNA testing has become a critical part of any major criminal investigation and some minor ones as well.

So here’s what you should know about DNA testing:

1. A DNA sample can be obtained from just a few cells of sweat, skin, hair, saliva, blood, semen, or any other bodily fluids. Even if several months have passed to a crime, identifiable DNA can still be found at the crime scene. And unless the criminal has been extra cautious, they are most likely to leave behind some bit of themselves at the crime scene.


2. DNA testing can more effectively prove someone innocent than guilty. When a DNA fingerprint is matched to a sample, each and every one of over ten elements must be equal. Any unequal element reflects that there is no definite match between the samples. In addition, a match is not always 100% accurate – it is just another piece of evidence.


3. There are two types of DNA testing.

i. RFLP, or Restriction Fragment Length Polymorphism, is commonly known as DNA fingerprinting. This DNA testing takes up to eight weeks and requires a sufficient quality sample, but its accuracy rate is one in three billion.

ii. PCR, or Polymerase Chain Reaction, is commonly known as an amplification test. This DNA testing takes one to three days and can be carried out on minimal sample, but it has 1-10% chance of providing a false positive.


4. A national database of DNA profiles, known as The National DNA Data Bank of Canada, is maintained by the Royal Canadian Mounted Police (RCMP) in Ottawa. The data bank holds of two types of DNA profiles:

i. a crime scene index that contains  DNA profiles retrieved from bodily substances that were found at a crime scene

ii. a convicted offenders index that contains DNA profiles retrieved from bodily substances of  post-conviction offenders as ordered by the DNA data bank.


5. Under the Canadian Criminal Code, judges can order those convicted of selected crimes to provide samples for DNA analysis. For purposes of the DNA Data Bank, offences are divided in 2 categories:

i. Primary designated offences – the most serious criminal offences - for example, murder and manslaughter, sexual offences and aggravated assault.

ii. Secondary designated offences – less serious crimes like arson.


If you have been charged with a crime, be sure to discuss the implications of a potential DNA test with your criminal lawyer in Toronto before your trial.

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