Polity, Law, Science & Technology, Forensic Science, Ethics, and Current Affairs.

Why the Court intervened

In a recent Tamil Nadu case, the Supreme Court found delay and poor handling of biological samples meant for DNA testing. Packets reached the lab late, seals/signatures were weak, and the chain of custody (who handled the sample, when and where) was unclear. When these gaps exist, contamination or mix-up cannot be ruled out, so the Court issued uniform directions for police, doctors and labs across India.

Typical lapses the Court wants to end

• Samples lying for weeks in the police store room (malkhana) or travelling without temperature care.
• Broken/unclear seals, missing signatures, or re-sealing without court order.
• No single register tracing the sample from collection → transport → lab → court.
• Trial courts receiving the DNA report without the supporting paperwork.

Genes and Genetics: Clear Explanations

Think of the body as a city, cells as houses and the nucleus as the locker. In the locker sits DNA (Deoxyribonucleic acid)—the instruction book of life—arranged in 23 pairs of chromosomes. Small stretches of DNA carrying instructions are genes. We inherit half our DNA from the mother and half from the father, so each person’s DNA pattern is unique (except identical twins).

For forensics, labs do not read health genes. They test harmless markers called STRs (Short Tandem Repeats)—short repeating pieces of DNA that differ from person to person. Testing many STR spots gives a DNA profile.

• DNA, or deoxyribonucleic acid, is the hereditary material in humans and nearly all other living organisms. It is a complex molecule that contains all the information needed to build and maintain an organism.
• DNA profiling, also known as DNA fingerprinting, is a forensic technique that identifies individuals by analyzing unique, variable patterns in their genetic code.
• Allele / Locus: An STR locus is the spot tested; the count/variant seen there is an allele.
• Short tandem repeats (STRs) are sequences of 1–6 base pairs of DNA that are repeated multiple times in a row at specific locations in the genome. Also known as microsatellites, these repetitive DNA sequences are highly polymorphic, meaning the exact number of repeats varies significantly among individuals. This high degree of variation makes STRs valuable markers in genetics and forensic science.
• PCR: A copying method that multiplies tiny DNA so it can be tested.
• Nuclear DNA vs mtDNA: Nuclear DNA is unique to a person; mitochondrial DNA (mtDNA) comes only from the mother and helps when testing hair shafts or very old bones.
• Y-STR: STRs on the Y-chromosome, useful when male DNA is mixed with female DNA in sexual-offence cases.
• Degradation / Inhibition: Heat, time, moisture break DNA (degradation); dirt/chemicals block PCR (inhibition).
• Mixture/low template: DNA from more than one person or very little DNA; needs stricter lab rules/software.
• How “match” is reported: Good labs give a random match probability (“one in a billion”) or a likelihood ratio (“X times more likely if it came from the accused”). Bigger numbers = stronger evidence.

What the Supreme Court has ordered

The Court has converted good practice into must-follow procedure. Every State must circulate formats and instructions down to districts.

• Standard forms + Chain-of-Custody Register: DGPs must issue sample collection forms and a register format; the register must be attached to the trial record.
• Full documentation at collection: Record FIR number/date, sections of law, place/time, police station & serial number, names/designations; take signatures of the doctor, investigating officer (IO) and independent witnesses.
• Quick dispatch: The IO must ensure the sample reaches the concerned hospital/police station within 48 hours. Any delay must be explained in writing.
• No opening/re-sealing while the case or appeal is pending without the trial court’s order.
• Quality in the lab: FSLs must use validated methods and controls so results are dependable.
• Accountability: If there is any lapse, the IO must explain; courts must check the chain and the method before relying on the report.

How courts view DNA reliability 

The Supreme Court treats DNA as highly probative, but not magical. Value depends on how the sample was collected, sealed, stored, transported and tested. Courts have rejected DNA where samples sat for months in malkhana, came from open areas prone to contamination, or where the expert could not explain controls and statistics. Rule of thumb: method matters as much as result.

Best practice worldwide (what strong systems do—and we should too)

• Accredited/ Standard labs (ISO/IEC 17025), regular audits, blind proficiency testing of analysts.
• Good packaging: Air-dry, use paper bags/boxes (not plastic), tamper-evident seals with unique IDs, seal photos, barcode tracking.
• Cold chain & timelines: Prefer refrigeration/freezer for biologicals; 24–72 hour transport targets; log every handover.
• Standard sexual-assault kits with e-tracking (collected → submitted → tested).
• Two-analyst review: one tests, another independently checks interpretation.
• Transparent reports: give match statistics and openly state limitations (low DNA, mixtures).
• Privacy & retention: strict access logs, time-bound storage, removal of profiles when a person is cleared.

Quick role-wise checklist

Investigators

• Wear gloves/masks; air-dry and paper-pack; seal at source and photograph seals.
• Fill forms and chain register fully; send to FSL within 48 hours; record reasons if delayed.
• In sexual offences: collect reference samples, control swabs and clothes separately.

Prosecutors

• Put the register, collection memo, seal photos, and FSL SOPs on record; examine the expert.
• Ask for match statistics and proof of controls.

Courts

• Test chain and method before the match: seal integrity, delay explanations, lab accreditation, controls, and clarity of statistics.

Final Words: Is DNA by itself enough to convict?

Usually no. DNA is an expert opinion with great value, but it must fit the case story—time, place, opportunity. Courts prefer corroboration: CCTV, call data, last-seen, recoveries, motive, or eyewitnesses. Also, secondary transfer (DNA moving by touch) is possible; hence context plus a clean chain are crucial.

Exam Hook

Key takeaways

• No chain, no gain: a clean, complete chain of custody is essential.
• 48-hour rule: quick dispatch protects DNA from damage and doubt.
• Lab quality + clear numbers: validated methods and match statistics make evidence strong.
• DNA needs context: best used with other evidence, not alone.
• Privacy matters: strict access and time-bound retention build trust.

Mains (10–12.5 marks):
“Discuss the Supreme Court’s directions on handling DNA evidence and explain how chain of custody, lab quality and match statistics determine its probative value. Suggest two global best practices India should adopt.”

Prelims (1-liner):
The chain of custody records every handover of a sample from collection to court — True.

One-line brief

DNA is powerful science, but only clean collection, clean paperwork, and clean lab work turn it into powerful evidence.