DNA Profiling - A Criminal’s Worst Nightmare

DNA. Everything has it, and we humans share 99.9% of identical DNA. Whilst this may seem like a lot, that 0.1% has enough variations - roughly 3 million bases (SorensonForensics) - that can distinguish two different people. Different variations, such as short tandem repeats (STRs), can be used on crime scenes, where millions of different DNA samples are available, from the blood to hair to old skin cells and fingerprints. This in turn is then used to profile criminals or victims, hence the name DNA profiling.

How Does DNA Profiling Work?

DNA profiling, or genetic fingerprinting, is used to determine the differences between people by comparing the short sequences of repeating DNA, or STRs, which are microsatellites - strands of DNA 2-5 sequences long. The DNA is then reproduced by polymerase chain reactions (PCR) to make many copies of STR strands (YourGenome). DNA tags called ‘primers’ bond to the STR locations, with 22 locations being the current standard, and each have a fluorescent tag to easily identify. Afterwards, electrophoresis, a DNA separation technique based on size (National Human Genome Research Institute), is used to separate the fragments into size order, passing by a laser that activates the tag causing it to glow during and after the process (YourGenome).

How Do Forensic Teams Use This To Identify Criminals?

As said earlier, 22 different locations of the STRs are used to identify individuals, with each STR having a certain chance of being identical to another human. The Cumulative Random Match Probability (RMP) system is a program used to find the probability of each different type of marker or STR occurring in individuals. From this, the RMP system can be used to trace identities. Whilst there are only 22 loci for the STRs, you have to multiply all of the percentage RMPs together, leading to a chances of more than 1 in one quadrillion to have the same STRs as each other (DNAConsultants). From this process, data from crime scenes can be compared to the DNA of suspects, taken from their fingerprints or hair samples, and the criminal can be officially arrested!

Application in Crime Solving

Database searching can also be completed using the CODIS or the National Forensic Database for the US or UK respectively. Partial matches can be flagged when doing searches, and from there background checks are completed and suspects can be taken in for samples and questioning. This has been most famously used to take in the Golden State Killer or Joseph James DeAngelo, a rapist, serial killer and burglar in the 1980s. He was arrested nearly 40 years later in 2018, after various results from STR analysis concluded the DNA match from the crime scenes (Wikipedia) (Medium).

The science and technology of forensics is constantly evolving with biological advances, and have been critical in solving crime cases that may have often been deemed unsolvable. The complex process of STR analysis is but one of the many ways that DNA profiling can be conducted, with options from Y-Chromosome analysis used to identify male rape cases to mitochondrial DNA analysis used in degraded skeletal remain cases all being used currently dependent on the crime. With constant breakthroughs in forensics and criminology, we will hopefully see crime rates drop in the future - after all, a criminal’s worst enemy is their own DNA.

Bibliography

"What Is DNA Profiling?" YourGenome, Wellcome Genome Campus, https://www.yourgenome.org/theme/what-is-dna-profiling/. Accessed 17 Feb. 2025.

"A Deep Dive into STR Analysis." Sorenson Forensics, https://sorensonforensics.com/a-deep-dive-into-str-analysis/. Accessed 17 Feb. 2025.

"Random Match Probability." DNA Consultants, https://dnaconsultants.com/random-match-probability/. Accessed 17 Feb. 2025.

Ali, Kasif. "The Science Behind the Golden State Killer's Capture." Medium, 30 Oct. 2023, https://medium.com/@kasifaliwdr/the-science-behind-the-golden-state-killers-capture-ffac9e61bb6d. Accessed 17 Feb. 2025.

"Joseph James DeAngelo." Wikipedia: The Free Encyclopedia, Wikimedia Foundation, https://en.wikipedia.org/wiki/Joseph_James_DeAngelo. Accessed 17 Feb. 2025.

"Electrophoresis." National Human Genome Research Institute, https://www.genome.gov/genetics-glossary/Electrophoresis. Accessed 17 Feb. 2025.

"DNA Fingerprinting: A Powerful Tool for Forensics and Beyond." Integra Biosciences, https://www.integra-biosciences.com/global/en/blog/article/dna-fingerprinting-powerful-tool-forensics-and-beyond. Accessed 17 Feb. 2025. (Fingerprint Cover Photo)