For those that watch television crime dramas, the use of DNA evidence appears to be the final nail in the conviction coffin. Television portrays DNA as direct evidence; evidence that proves the existence of the fact without the use of interferences or presumptions. In reality, DNA is wholly circumstantial in nature. In this paper I will be focusing on what DNA is, how it is used, and what issues and limitations it has.
First off, deoxyribose nucleic acid, better known as DNA, is cellular coding that has to do with how we develop, grow, and function. In simpler terms, it is the code that makes up who we are. However, as unique as we like to believe ourselves to be, human DNA is 99.9% identical, leaving only 0.1% of our DNA to be different. It is this small portion of unique DNA that is used to create our DNA profile (Elster).
A DNA profile usually consists of a graphs with certain peaks showing where our DNA is probably unique. In an ideal situation, the graph would have at least 16 points where the DNA can be sketched out to create DNA fingerprint. However, if the DNA is damaged, as in cases where it is exposed to moisture or extreme temperatures, only a fraction of these markers may be available and a forensic team may only be able to determine a partial profile (Elster).
An analogy I like to use is that a complete DNA profile is similar to complete description of your appearance, while a partial profile is akin to describing only some of your traits, like hair color or height. You probably share a similar hair color with many other individuals. Like so, a partial DNA profile can match us between many people as well. More surprisingly, even a complete DNA profile could match up with more than one person. That’s not even the end of the problem. To make things even more complicated, DNA profiles can even be mistakenly generated if a sample is contaminated (Elster).
One example of a DNA mixup was in 2011 when Adam Scott was wrongully accused of rape that occured in a city, more than 200 miles from here he lives, Scott never visited. The error was due to a mishap in the lab, where the plate containing Scott’s DNA that was being used from a mnir incident was accidently reused in a rape case (senseaboutscience, page 7).
Furthermore, the presence of DNA at a crime scene is not enough to prove the fact of someone involved with a crime. DNA recovered at the scene of a crime could have been deposited there at a time other than when the crime occured. It could have been left there long before, or even after the fact. It could have even been left there as a result of a secondary transfer, where an individual’s DNA was transferred on to someone else, and they carried onto the scene (Elster).
The American Bar Association has backed the use of DNA uvidence in the courtroom, but has urged caution with how it is interpreted.
Additionally, DNA profiling technology has been gradually getting better and better at detecting and identifying smaller and smaller amounts of DNA evidence. This can be both a blessing and a curse. On one hand, it is able to use DNA fragments that earlier might have been unsalvageable. On the other, this technology is more likely to detect contanimations, such as secondary transfer of DNA, which can further confuse the investigation (Elster).
- Elster, Naomi. “How Forensic DNA Evidence Can Lead to Wrongful Convictions.” JSTOR Daily, 6 Dec. 2017, https://daily.jstor.org/forensic-dna-evidence-can-lead-wrongful-convictions/.