DNA fingerprinting, also known as DNA profiling, is a laboratory technique that analyzes unique patterns within an individual’s genetic code for identification. The method focuses on non-coding regions of DNA that contain highly variable repetitive sequences, which differ significantly between people. While over 99.9% of human DNA is identical, the remaining fraction contains distinct markers used to create a unique profile for every person, except identical twins. British geneticist Sir Alec Jeffreys discovered this concept in 1984.
Forensic Identification and Criminal Justice
The most recognized application of DNA fingerprinting is in the field of forensic science, serving as a powerful tool for law enforcement. DNA profiles are generated from biological evidence collected at crime scenes, such as blood, saliva, hair, or semen. This process involves isolating DNA and then analyzing specific regions known as Short Tandem Repeats (STRs), which are short nucleotide sequences repeated multiple times.
The length of these STRs varies significantly among individuals. Forensic scientists analyze multiple STR markers, typically 13 or more locations, to create a highly specific genetic profile. Analyzing this many markers yields a random match probability as low as one in several billion. A successful profile from crime scene evidence can be compared directly to the DNA profiles of suspects.
If a match is found, the DNA evidence provides a strong link between the suspect and the crime scene. Conversely, if the profiles do not match, the suspect can be reliably excluded from the investigation. DNA profiles are also stored in national databases, such as the Combined DNA Index System (CODIS) in the United States, allowing investigators to search for matches from previous offenders or unsolved cases. This technology is also used to review past convictions and exonerate individuals who were wrongly accused.
Establishing Biological Relationships
Beyond forensic identification, DNA profiling is frequently used to establish biological kinship, most commonly in paternity and maternity testing. This application relies on the inheritance pattern of genetic markers, as a child inherits half of their genetic material from each biological parent. Scientists analyze the same STR markers used in forensics to compare the child’s profile with that of a potential parent.
The child’s genetic profile must contain marker alleles that match those of both the mother and the father. If the alleged parent’s profile does not share the necessary markers with the child, paternity or maternity can be reliably excluded. This analysis is used for legal purposes, such as immigration, child support disputes, or inheritance claims, as well as for personal confirmation. The analysis can also determine sibling relationships or other familial connections.
Identifying Human Remains
DNA fingerprinting has become the standard method for identifying human remains when traditional methods like dental records or visual recognition are impossible. This application is relevant in mass casualty incidents, such as plane crashes, natural disasters, or military conflicts, where remains may be fragmented or decomposed. DNA analysis, often referred to as Disaster Victim Identification (DVI), works by creating a profile from the unidentified remains, known as a post-mortem sample.
A significant challenge in DVI is working with degraded DNA resulting from exposure to harsh environmental conditions. To overcome this, scientists rely on hard tissues like teeth and bone, as they offer better protection for the genetic material than soft tissues. If the nuclear DNA is too degraded, forensic geneticists may analyze mitochondrial DNA (mtDNA), which is more abundant and resistant to breakdown. The post-mortem profile is then compared to an ante-mortem sample or to reference samples from close biological relatives to confirm identity.
Applications in Wildlife and Conservation
The utility of DNA fingerprinting extends beyond human identification into wildlife biology and conservation. This technology is employed in wildlife forensics to combat illegal poaching and the unlawful trade of endangered species products. By analyzing trace samples, such as blood, feathers, or processed products, scientists can identify the species of origin.
DNA profiling can also link seized animal parts back to a specific crime scene or a known individual animal, similar to human criminal cases. In conservation efforts, genetic profiles help researchers track migration patterns, estimate population sizes, and assess genetic diversity within a species. This information is valuable for managing breeding programs and ensuring the health of endangered populations.