Scientific Foundations and Legal Framework

 Introduction

DNA evidence has revolutionized
forensic science and criminal investigations, providing unprecedented accuracy
in identifying biological materials and establishing connections between
suspects, victims, and crime scenes. However, the admissibility and probative
value of DNA evidence in criminal proceedings requires careful judicial
scrutiny of both its scientific methodology and procedural compliance.

Legal Classification: DNA as Opinion
Evidence

DNA evidence constitutes opinion
evidence under Section 45 of the Indian Evidence Act, and like any other
opinion evidence, its probative value varies from case to case. This classification requires courts to evaluate DNA
evidence with the same rigorous standards applied to expert testimony, ensuring
that the scientific foundation and methodology meet established legal
requirements.

Mitochondrial
DNA (mtDNA):
Circular, double-stranded DNA of 16,569 base pairs showing maternal
inheritance, particularly useful for degraded samples due to its presence in
large numbers of copies^[.

Y-Chromosome
Analysis:
Employed to trace male lineage and resolve DNA from males in sexual assault
cases, especially helpful in detecting male profiles despite high levels of
female DNA or in cases involving azoospermic or vasectomized males.

DNA Profiling Methodology

Four-Step Process

The DNA profiling process involves four
sequential analytical steps:

1.       Isolation,
purification and quantitation of DNA

2.       Amplification
of selected genetic markers

3.       Visualizing
fragments and genotyping

4.      Statistical
analysis and interpretation

Statistical Analysis Framework

DNA profile comparison yields three
possible outcomes:

Match: DNA profiles from evidence and
reference samples are indistinguishable, requiring statistical support through
Random Match Probability (RMP) calculations that estimate the frequency of the
particular DNA profile in a population.

Exclusion: Profile differences indicate
different biological sources, providing definitive exclusionary evidence.

Inconclusive: Insufficient data prevents definitive
conclusions.

Evidence Collection and Preservation
Standards

Legal and Scientific Requirements

DNA evidence must be properly
documented, collected, packaged, and preserved to meet both legal and
scientific requirements for court admissibility. The extremely small sample sizes used
in DNA analysis necessitate heightened attention to contamination issues during
evidence handling.

Contamination Prevention

Contamination can occur when DNA from
another source mixes with case-relevant DNA, potentially happening through
sneezing, coughing, or touching contaminated surfaces after contact with mouth,
nose, or face. Proper identification, preservation, packaging, and
transmission protocols are essential for maintaining evidence integrity.

Judicial Standards and Quality Control

International Guidelines

Following the UK Court of Appeal
decision in R v. Dohoney & Adams, courts should require:

·      
Expert
testimony on DNA comparisons with random occurrence ratio calculations

·      
Prosecution
disclosure of calculation methodologies to defense

·      
Defense
expert access to databases underlying the calculations

Indian Judicial Approach

The Law Commission of India observed
that while DNA evidence involves genetic material comparison, matching samples
do not conclusively prove identity but rather provide statistical probability
data. The Commission noted that DNA may be more useful for
investigative purposes than for raising presumptions of identity in court.

Quality Assurance Requirements

Courts have emphasized that DNA profile
validity and reliability depend on quality control and quality assurance
procedures in laboratories. The Supreme Court has noted that mere
exhibition of DNA reports without examining their underlying basis renders such
evidence “highly vulnerable”.

Judicial Observations on DNA Evidence

Reliability and Limitations

Courts have recognized that DNA testing
provides “powerful new evidence unlike anything known before,”
enabling determination of biological tissue matches “with near
certainty”. However, judicial scrutiny must examine whether DNA
techniques were reliably applied by experts and consider possibilities of
sample tampering during storage periods.

Procedural Safeguards

The reliability of DNA evidence depends
critically on:

·      
Proper
sample collection and sealing procedures

·      
Maintenance
of chain of custody

·      
Laboratory
quality control measures

·      
Expert
testimony regarding methodology and statistical calculations

Contemporary Legal Significance

DNA testing has both exonerated wrongly
convicted individuals and confirmed valid convictions, demonstrating its dual
capacity for establishing truth in criminal proceedings. However, courts must balance the powerful probative value
of DNA evidence against the need for procedural compliance and methodological
rigor.

Conclusion

While DNA evidence represents a
significant advancement in forensic science, its admission in criminal
proceedings requires careful judicial evaluation of both scientific methodology
and procedural compliance. Courts must ensure that DNA evidence meets established
quality standards for collection, analysis, and statistical interpretation
before according it probative value in determining guilt or innocence. The
classification of DNA evidence as opinion evidence under existing legal
frameworks provides the necessary analytical structure for judicial scrutiny
while recognizing its unique scientific foundations and capabilities.

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