DNA is present in each of our cells and contains the instructions that allow our bodies to function. Each of our DNA patterns are different, just as our bodies differ. The only exception to this rule is identical twins. Criminologists can use DNA present at a crime scene to determine who was present when the crime was committed by comparing these patterns. While there are several benefits in using DNA analysis to solve crimes, there are still some drawbacks that must be considered.
Your Unique DNA Fingerprint
The chance of a DNA match between two persons who aren't twins is from 1/7000 to 1/1,000,000,000, depending on the frequency of the patterns being compared. This is a much more specific test than other methods such as blood type, and DNA is present in any of kind of body tissue, so it is more likely to be found at a crime scene than blood. DNA testing is also more reliable than eyewitness testimony.
Small Sample Sizes
Because DNA can be amplified in the laboratory using a process called polymerase chain reaction, an amount of tissue as small as 10 microliters may be sufficient to perform identity testing. This also allows the police to send small samples to multiple independent labs, reducing the possibility of an error affecting the results. DNA is also more stable than the proteins contained in blood. Therefore it can be used to solve cases that are older and in which the samples may be more degraded, or which have been exposed to materials such as solvents or detergents.
Disadvantages of DNA Analysis
There is no consensus on what should happen to DNA samples once they have been taken. Some jurisdictions hold on to samples for years, even when the suspect has been cleared of any guilt. Police may try to use the samples to look for matches when investigating future crimes. Storing DNA may also lead to the possibility that insurance companies will access the samples to test individuals for diseases that are caused by genetic defects.
Personal rights advocates argue that storing DNA is unethical for several reasons. For example, when someone has been proved to be unrelated to a crime by a DNA sample, but then is matched to a different crime for no other reason than that sample on file, it is questionable whether the police had probable cause to use the collected DNA as evidence.
Additionally, minorities are arrested at a higher rate than the general public, and many jurisdictions take DNA samples from anyone who has been arrested. Therefore, minorities may be overrepresented in the DNA bank. It may be easier to find minority criminals even when the only evidence that connects him to the crime is the sample. Criminal defence attorneys fear police may focus investigation efforts on crimes where there is already a DNA match, rather than on all crimes, resulting in even higher conviction rates for minorities.
- Human Genome Project: DNA Forensics
- "Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers"; John Marshall Butler; 2005