DNA Testing in Sexual Offences

DNA Testing in Sexual Offences - Code of Life Clues

• Principle: Compares suspect's DNA with evidence from victim/scene.
• Sources: Semen, blood, saliva, hair (with root), epithelial cells, vaginal swabs.
• Types of DNA:
  • Nuclear DNA (nDNA): Unique to individual (except identical twins).
  • Mitochondrial DNA (mtDNA): Inherited maternally; useful for degraded samples/hair shafts.
• Techniques: While PCR-based STR analysis remains standard, massively parallel sequencing (MPS) offers improved capabilities for analyzing low-quantity or degraded DNA samples and distinguishing between monozygotic twins.
• Significance: Identification, exclusion, linking individuals, establishing contact under BSA provisions.

⭐ Alec Jeffreys is known as the father of DNA fingerprinting.

• Chain of Custody: Crucial for admissibility under BSA framework. 📌 Standard procedures involve detailed documentation of collection, packaging, sealing, preservation, transportation, and analysis, ensuring unbroken accountability record per BNSS protocols.

DNA Testing in Sexual Offences - Trace, Tag, Testify

• Trace (Sources of DNA):
  • Semen (spermatozoa, seminal fluid: Acid Phosphatase, p30/PSA)
  • Saliva (e.g., bite marks, oral swabs)
  • Blood (victim's, assailant's)
  • Hair (plucked, with root/sheath)
  • Epithelial cells (skin, vaginal/anal/oral swabs, fingernail scrapings)
• Tag (Collection & Preservation):
  • Use sterile Sexual Assault Evidence Collection Kit (SAECK).
  • Air-dry all moist evidence (swabs, clothes) before packaging.
  • Package items separately in labelled paper bags/envelopes.
  • Rapid drying is critical to prevent degradation. While 4°C is acceptable for short-term storage, freezing at -20°C or -80°C is preferred for long-term preservation.
  • Meticulous Chain of Custody (CoC) is vital.
• Testify (Analysis & Legal Value):
  • Standard: PCR-based STR (Short Tandem Repeats) analysis remains widely used.
  • Massively Parallel Sequencing (MPS/NGS) increasingly adopted for degraded/low-quantity samples with enhanced capabilities.
  • Yields DNA profile for comparison (suspect, victim, CODIS).
  • Strong corroborative evidence: links or excludes.

⭐ The two-finger test is banned and unscientific; DNA evidence is preferred for corroboration in sexual assault cases under BNS provisions.

DNA Testing in Sexual Offences - Unraveling the Strands

DNA fingerprinting is pivotal in sexual offence investigations, linking suspects to crime scenes or excluding innocents with high accuracy.

• Principle: Exploits unique hypervariable regions in an individual's DNA (except identical twins).
• Common Sources:
  • Semen (vasectomized males shed cells), blood, saliva
  • Vaginal, anal, oral swabs
  • Fingernail scrapings, plucked hair (root), skin cells
• Core Techniques:
  • PCR (Polymerase Chain Reaction): Amplifies minute/degraded DNA.
  • STR (Short Tandem Repeat) Analysis: Gold standard; examines 20 specific, variable loci (expanded from original 13 in 2017).
  • Y-STR Analysis: For male DNA in mixed samples (e.g., azoospermic assailant).
  • mtDNA Analysis: For hair shafts, old bones; maternally inherited.

⭐ Combined DNA Index System (CODIS) uses a standard set of 20 STR loci (expanded from 13 as of January 1, 2017) for creating DNA profiles.

• Significance: Provides powerful associative evidence; crucial for corroboration and justice. Exonerates the wrongly accused.

DNA Testing in Sexual Offences - Justice by Genes

• Role: Links suspect to victim/scene via unique genetic profile in sexual assaults.
• Legal Framework (India):
  • BNSS: Sec 53, 211 (DNA from rape accused), 164A (victim exam).
  • BSA: Sec 12 (identity), Sec 39 (expert opinion).
• Admissibility: Strong corroborative evidence; expert opinion (Sec 39 BSA).
• Samples: Blood, semen, saliva, hair, skin. Chain of custody crucial.
• Analysis: PCR-based STR profiling standard; NGS/MPS for complex cases.
• Challenges: Contamination, degradation, mixed DNA, interpretation.
• Ethics: Consent (victim), privacy, data security.

⭐ Under Section 211 BNSS, an accused of rape can be examined by a medical practitioner, which includes collection of samples for DNA profiling, even without consent if necessary as per law.

High‑Yield Points - ⚡ Biggest Takeaways

• DNA evidence is paramount in sexual offense cases, primarily from semen, saliva, or blood.
• Short Tandem Repeats (STRs) are the most commonly analyzed DNA markers.
• Maintaining a strict chain of custody is vital for legal validity.
• Proper sample collection and preservation (e.g., air-drying, paper bags) prevents DNA degradation.
• DNA can link a suspect to the crime or exonerate the innocent.
• Consent is generally required for reference sample collection from individuals involved.