What is DNA fingerprinting? Explain the mechanism and applications of DNA fingerprinting in forensic science.

Mechanism of DNA Fingerprinting

The process of DNA fingerprinting involves several key steps that capitalize on the unique variations in an individual's DNA, particularly in regions known as Variable Number Tandem Repeats (VNTRs) and Short Tandem Repeats (STRs).

1. Sample Collection: The first crucial step involves collecting biological samples containing DNA from the crime scene or individuals. These can include blood, saliva, hair (with follicle), semen, skin cells, bone, or any other tissue.
2. DNA Extraction: Once collected, DNA is isolated from the cells in the sample. This involves lysing the cells to release the DNA and then purifying it from other cellular components like proteins and lipids.
3. DNA Amplification (PCR): Often, the amount of DNA obtained from a crime scene is minuscule or degraded. The Polymerase Chain Reaction (PCR) technique is used to amplify specific target regions of the DNA, typically STRs, to create millions of copies. This ensures sufficient material for subsequent analysis.
4. Restriction Digestion (Older Methods) / STR Analysis:
   • Earlier methods (RFLP - Restriction Fragment Length Polymorphism): Involved cutting the DNA at specific recognition sites using restriction enzymes, producing fragments of varying lengths.
   • Modern methods (STR Profiling): Focus on Short Tandem Repeats (STRs), which are short sequences of DNA (2-6 base pairs) that are repeated multiple times. The number of repeats at a particular locus varies significantly between individuals. Fluorescent labels are attached to the amplified STRs.
5. Separation (Gel Electrophoresis/Capillary Electrophoresis):
   • Gel Electrophoresis (older): DNA fragments are loaded onto an agarose gel. An electric current is applied, causing the negatively charged DNA fragments to migrate towards the positive electrode. Smaller fragments move faster and further than larger ones, separating them by size, creating a unique banding pattern.
   • Capillary Electrophoresis (modern): Amplified, fluorescently labeled STR fragments are passed through a thin capillary containing a polymer matrix. A laser detects the fluorescence, and a detector records the size and intensity of each fragment, generating an electropherogram (a graphical representation of the DNA profile).
6. Analysis and Comparison: The resulting DNA profile (banding pattern or electropherogram) is compared to reference samples (e.g., from suspects, victims, or databases). A match indicates that the samples likely originated from the same person. Statistical analysis determines the probability of a random match, making the evidence highly reliable.

Applications of DNA Fingerprinting in Forensic Science

DNA fingerprinting has become an indispensable tool in forensic science, transforming criminal investigations and legal proceedings globally, including in India.

• Criminal Investigations:
  • Linking Suspects to Crime Scenes: Biological samples (blood, semen, hair, skin) found at a crime scene can be profiled and compared with a suspect's DNA, providing strong evidence for conviction or exoneration.
  • Exoneration of the Wrongfully Accused: DNA evidence has been crucial in re-examining old cases, leading to the release of individuals wrongly convicted years ago.
  • Identification of Repeat Offenders: DNA databases (where established) allow law enforcement to link DNA from unsolved cases to profiles of previously convicted criminals, identifying repeat offenders.
  • Solving Cold Cases: Advancements in DNA technology, including forensic genealogy and improved handling of degraded samples, enable the reopening and solving of cold cases decades after the crime.
• Paternity and Maternity Testing:
  • It accurately determines biological parentage by comparing the DNA profiles of a child with alleged parents. This is vital in family disputes, inheritance cases, and immigration matters.
• Identification of Unidentified Remains and Disaster Victims:
  • DNA profiling is used to identify human remains in cases of natural disasters (e.g., floods, earthquakes), accidents, mass casualties, or decomposed bodies, by comparing their DNA with samples from presumed relatives or personal effects.
• Wildlife Forensics:
  • Helps in combating poaching and illegal wildlife trade by identifying species or individual animals from confiscated samples (e.g., ivory, animal parts, meat), aiding in conservation efforts and prosecution.
• Immigration Cases:
  • Used to verify familial relationships for immigration purposes, ensuring legitimate family reunification.

Legal Framework and Challenges in India:

While DNA fingerprinting is widely accepted, India's legal framework is still evolving. The Criminal Procedure (Identification) Act, 2022, replaced the Identification of Prisoners Act, 1920, and empowers law enforcement to collect, store, and analyze biological samples, including DNA, from convicts and certain categories of accused persons. However, concerns regarding privacy, data security, and the establishment of a national DNA database have been debated extensively, particularly concerning the previously proposed DNA Technology (Use and Application) Regulation Bill, which was withdrawn in 2023. The Indian legal system generally accepts DNA evidence as corroborative rather than conclusive, emphasizing the need for robust Standard Operating Procedures (SOPs), quality infrastructure, and trained personnel in forensic laboratories.