Syllabus: GS3/Science & Technology
Context
- Investigators are using DNA profiling to determine the suspect of the recent deadly car explosion outside the Red Fort in New Delhi, highlighting how genetic analysis plays a crucial role in forensic investigations.
About DNA Profiling
- It is a set of molecular techniques used to identify individuals based on unique genetic markers.
- It remains the most dependable method of identification in cases involving explosions, fires, or mass disasters where bodies are unrecognisable.
| Deoxyribonucleic Acid (DNA) – It is a molecule composed of two strands forming a double helix, carrying genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms. – Each DNA molecule consists of four chemical bases: adenine (A), thymine (T), cytosine (C), and guanine (G). 1. The sequence of these bases determines genetic information. |
Principles of DNA Profiling
- Short Tandem Repeats (STRs) as the most widely used markers.
- Each person has a distinctive STR pattern.
- Children inherit 50% of STR markers from each parent.
- A match between the mother’s STR profile and that of an unidentified body can confirm identity with high accuracy.
- Single Nucleotide Polymorphisms (SNPs) for higher resolution, useful for ancestry and medical applications.
- Mitochondrial DNA (mtDNA) and Y-chromosomemarkers for lineage tracing. If nuclear DNA is too degraded:
- mtDNA is used because it survives extreme conditions.
- It is inherited only from the mother.
- It is crucial for confirming maternal lineage, while it cannot uniquely identify individuals.
Techniques in DNA Profiling
- Polymerase Chain Reaction (PCR): It allows amplification of small or degraded DNA, and enables analysis of STR loci.
- Capillary Electrophoresis: It separates DNA fragments by size to generate STR profiles, and produces electropherograms used in identification.
- Next-Generation Sequencing (NGS): It provides sequence-level variation of STRs and SNPs, and enables deeper resolution in ancestry mapping and complex forensic cases.
Applications of DNA Profiling in Genetic Analysis
- Forensic Identification: Crime scene investigation, missing-person cases, mass-disaster victim identification.
- Medical Genetics: Detection of hereditary disorders using SNP-based profiling.
- Pharmacogenomics: matching drugs to patient genetic profiles.
- Evolutionary and Population Genetics: Tracing migrations, genetic drift, founder effects.
- Measuring genetic diversity in populations.
- Ancestry and Genealogy Testing: Comparing customer DNA to population reference panels.
- Use of autosomal SNP arrays and haplogroup analysis.
- Conservation and Wildlife Biology: Tracking illegal wildlife trade.
- Identifying species, subspecies, and individuals in ecological studies.
| How Genetic Analysis Establishes Identity? – DNA Extraction: Samples are taken from biological material — blood, bone, hair, or tissue — from both the unidentified remains and the known relative. – PCR Amplification: PCR is used to amplify specific DNA regions for comparison. – STR Profiling: STRs are highly variable DNA sequences used to create a genetic profile. – Kinship Matching: The suspect’s DNA is compared with that of the relative to establish a biological relationship. |
Challenges in DNA Identification
- Degraded DNA: Heat, chemicals, or environmental exposure can break down genetic material.
- Contamination: Poor handling or mixing of samples can compromise results.
- Insufficient DNA: Some remains may yield very little biological material.
- Mixed Profiles: In explosions, remains of multiple individuals may be intermingled, complicating analysis.
India & DNA Technology
- The DNA Technology (Use and Application) Regulation Bill, 2019 was aimed to regulate the use of DNA technology for establishing identity in criminal investigations, missing persons cases, and disaster victim identification.
- The bill, though not passed, was aimed to:
- Establish a DNA Regulatory Board;
- Set standards for DNA laboratories;
- Ensure privacy and ethical use of genetic data.
- The bill, though not passed, was aimed to:
- The Criminal Procedure (Identification) Act, 2022 allows for the collection of DNA samples from arrestees, undertrials, and convicts.
- The Department of Biotechnology (DBT) under the Ministry of Science & Technology supports research and infrastructure for DNA-based technologies, including biobanks and genomic studies.
Ethical, Legal, and Social Issues
- Privacy concerns and genetic data protection.
- Risks of genetic discrimination in insurance/employment.
- Debates around national DNA databases.
- Informed consent and data ownership in consumer genetic platforms.
| Other Methods of Genetic Analysis – Mendelian (Classical) Genetics: 1. Segregation & Independent Assortment Analysis: Used to determine how traits pass from parents to offspring based on predictable ratios. 2. Linkage & Recombination Mapping: Measures how frequently alleles recombine during meiosis to infer physical proximity on chromosomes. – Cytogenetic Methods: 1. Karyotyping: Examines whole chromosome structures to detect aneuploidies and gross chromosomal changes. 2. Fluorescence In Situ Hybridization (FISH): Uses fluorescent probes to detect specific DNA sequences on chromosomes. 3. Comparative Genomic Hybridization (CGH): Identifies chromosomal gains and losses without requiring cell culture. – Functional Genetic Analysis: 1. Gene Knockout/Knock-in (CRISPR, TALEN, ZFN): Used to study gene function by disrupting or altering gene sequences. 2. RNA Interference (RNAi): Silences gene expression to observe phenotypic changes. 3. Overexpression Systems: Increase gene expression to determine function. – Epigenetic Analysis: 1. Bisulfite Sequencing: Maps DNA methylation. 2. ChIP-seq: Identifies protein–DNA interactions and histone modifications. 3. ATAC-seq: Profiles chromatin accessibility. |
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