Human samples that contain cells with nuclei such as saliva, semen, urine and hair can be applied to DNA tests to determine one’s identity. They are extremely sensitive thus enabling it to be more reliable in results and it can also be conducted using samples that are to small for other serological tests. DNA is also withstanding as it repels degeneration even after being contaminated with chemicals or bacteria. Its ability to aid the police in a crime investigation by excluding suspects allowing the police not to waste time on investigating suspects and its specificity makes DNA profiling an extremely reliable way to compare a suspect’s DNA with material evidence found at the crime scene. It is highly accurate as in a test with 13 markers (typically compared number of markers from the DNA in two samples), the probability that any two individuals would have identical profiles is estimated to be below 1 in 10 billion. DNA profiling is an ideal method for confirming an identity with almost utmost certainty. It’s easy and painless to obtain a specimen for testing and a thorough, affordable and reliable scientific test can be conducted in as little as 48 hours. Most labs also run the DNA results through two different analyzers, eliminating the minor chance of inaccuracy.
However contrary to popular belief, DNA profiling is not foolproof as it also has its limitations. It like many other techniques in forensic science is susceptible to human error and contamination of samples during specimen analysis or collection may produce faulty results as the complexity of testing and data storage also mean that there is a higher chance that errors could occur. As a DNA test should be run on multiple samples, at least twice, collecting four samples and running every test twice to avoid false readings.
Older DNA profiling technologies are also more prone to errors, which could give false-negative or false-positive results.
DNA dragnets, operations where police collect samples from a large number of people in a geographic region to find a culprit, have proven especially controversial. DNA profiles can only offer statistical probability (for example, one in a million), rather than absolute certainty and the more people tested, the lower the statistical probability. For instance, the probability of one in a million may descent to one in 10,000 if enough people are profiled for a single test.
DNA databases stored on computer are vulnerable to exploitation through hackers, it is also extremely tedious to build a DNA database and DNA evidence is easily planted at a crime scene leading to Concerns that the finding of trace amounts of DNA can falsely implicate a person in a criminal investigation.
Many people are also against holding a person’s DNA profile on record as they feel strongly that it is a violation of that person’s DNA ‘ownership’ and poses strong ethical quandaries and is a civil infringement when authorities keep samples from people who have never been accused of any crime.
DNA evidence is one of many types of evidence jurors should take into account when considering a case, however it should not be considered as the main air-tight evidence which is contrary to public belief due to the ‘CSI effect’. This implies that TV shows like "CSI" may have popularized forensic science to the point where some jurors have unrealistic expectations of DNA analysis and accord it more weight than other types of evidence, leading to an unfair unjust sentence of the convicted suspects.
There is also a pressing concern that DNA profiles could be related to certain illnesses and character traits, and this information would be used by insurance companies and other organizations to the disadvantage of the individual.
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