By Dr. Alex Tan – Updated Aug 30, 2022
DNA profiling is a cornerstone of modern forensic science, enabling investigators to identify individuals based on their unique DNA signature. First pioneered by Sir Alec Jeffreys in 1984, DNA fingerprinting has become an indispensable element of the forensic toolkit.
Jeffreys discovered that the human genome, though too vast to sequence entirely, contains short, highly variable segments—short tandem repeats (STRs)—that differ markedly between people. These STR loci provide a practical means of individualizing DNA samples without the need for full genomic sequencing.
Today, forensic laboratories analyze 13 specific STR loci to generate a DNA profile. According to the Human Genome Project (HGP) website, evaluating this number of loci balances discriminatory power with operational efficiency, keeping costs and turnaround times manageable while maximizing the likelihood of a unique match.
Restriction enzymes, often referred to as restriction endonucleases, act like molecular scissors. They recognize and cleave DNA at specific, short sequence motifs, producing fragments whose lengths reflect the underlying genetic variation.
When a blood sample is recovered from a crime scene, DNA is first extracted and purified. The 13 target STR regions are then isolated using restriction enzymes that cut adjacent to each locus, effectively excising these segments from the surrounding genomic DNA.
Next, the isolated STR fragments undergo a second round of enzymatic digestion. The resulting fragments—whose sizes vary between individuals—are separated on an agarose gel. This electrophoretic step visualizes the fragment lengths, producing a banding pattern that serves as a genetic fingerprint.
The variability of restriction sites across individuals ensures that each person’s DNA yields a distinctive pattern of fragment sizes. By comparing the crime‑scene profile to suspect profiles across all 13 loci, forensic scientists can confirm or exclude potential matches with high confidence.
Restriction enzymes remain a vital resource in forensic genetics, enabling rapid, reliable, and cost‑effective DNA profiling that aids law‑enforcement agencies worldwide.
