Daily Archives: November 18, 2009

Dirty DNA

There is no doubt that DNA profiling is a powerful tool in criminal investigation. Its ability to identify an individual or place someone at the scene of the crime or connect someone to a murder weapon is its primary usefulness.

DNA profiling depends upon good quality and uncontaminated DNA. To develop a DNA Fingerprint, the sequence of the bases that make up the DNA chain must be intact. That is, the chain can’t be broken into pieces. If the DNA has been damaged by heat, acids, decay, or other circumstances, the DNA strands tend to be fragmented and therefore the sequence cannot be accurately determined. This can make any DNA useless from a forensic point of view.

Contaminants can also interfere with DNA testing. How many times have you seen on TV or read in the paper about DNA being obtained from discarded cigarettes or soda cans? The small amounts of DNA that would be found on a cigarette butt or the lip of a can are typically subjected to Polymerase Chain Reaction (PCR) amplification. This is a technique where enzymes known as polymerase enzymes are added to the DNA sample. The enzymes cause a replication, or duplication, of the DNA strands by a process that is very similar to what the body does naturally when DNA is copied as part of the complex cell division sequence. Unfortunately, things like tobacco and aluminum can interfere with the function of these enzymes and therefore the DNA cannot be amplified. The result is that the inability to obtain enough DNA from a very small sample to use in the profiling process is hampered if not rendered impossible.

But apparently all is not lost. Johannes Hedman and his team at the Swedish National Laboratory of Forensic Science have come up with three other polymerase enzymes that circumvent this problem. These enzymes, which have not typically been used in the forensic arena, seem to be oblivious to contaminants such as tobacco and aluminum and therefore are useful for amplifying contaminated DNA samples. If this pans out, this will be a very useful new tool for the DNA analyst.

If you want to read an excellent article on exactly how DNA profiling is done then go HERE.

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Posted by on November 18, 2009 in DNA, General Forensics, High Tech Forensics

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