You hear about DNA analysis everywhere you go – it’s in the news, and on television shows like CSI. Today, DNA analysis is used not only to resolve questions of paternity, but also to place suspects at crime scenes. There’s no question DNA analysis is hot – but what exactly is it?
Let’s take a step back and first understand a bit about DNA. DNA is hereditary biological material that is found in almost every cell in the human body. DNA is made up of sections of repeating sequences of genetic information. The sequences differ from person to person, so every person has a unique set of DNA. The only people who have the same DNA are identical twins.
The uniqueness of DNA makes it possible to use DNA from a crime scene to either connect a suspect to the scene or eliminate a suspect from consideration. DNA can be collected from virtually any surface that contains human cells in the form of blood, skin cells, hair, saliva, etc.
In the context of crime scene investigation, DNA analysis is the process of analyzing two sets of DNA to determine if they are from the same person. This is no simple task, because the vast majority of each set of DNA (99.9%!) is the same from person to person. Forensic scientists examine a number of critical regions of the DNA samples. If the sequences of genetic information from each sample match in these regions, then the samples are from the same person.
Before DNA can be analyzed, it must be collected. When a crime is committed, crime scene investigators scour the scene for possible sources of DNA evidence. DNA analysis requires only a few cells, so critical evidence in a case could be extracted from something as seemingly inconsequential as saliva on a toothpick or sweat on a pair of eyeglasses. After locating biological evidence, crime scene investigators must document in detail its location and condition. Only then can they begin to collect a sample, taking utmost care not to contaminate their discovery. But the documentation portion of the job is not over. Once the evidence is collected, crime scene investigators begin a meticulous record of the individuals who handle or transport the evidence as it makes its way to the forensic laboratory, where DNA analysis occurs.
Forensic scientists who analyze DNA evidence in the lab are typically called DNA analysts. The DNA analyst’s job begins when a sample of biological evidence arrives at the lab from the scene of the crime. The DNA analysis process consists of several steps. First, the analyst must extract the DNA from the evidence sample. Then, he or she processes the DNA to determine the DNA sequence in the critical DNA regions. When there is a suspect in the case, the analyst must extract and process the DNA sample from that person. Only then can the analyst compare and interpret the results from the two samples to determine if they are from the same person.
The DNA analyst must take detailed notes during every step of the process. These notes are used to write a full report about the analysis and its conclusions. If the DNA evidence is used in a case that goes to trial, the DNA analyst may be required to testify in court about the work. In many instances, it is the DNA evidence that cinches the case!
DNA analysis techniques have improved dramatically with time, and this field of forensic science promises to be increasingly important in years to come.
About the author: Emily Nelson earned an M.S. in Electrical Engineering from the Massachusetts Institute of Technology before beginning her career as a science writer.