Relevance: Science & Technology-GS2-Sec3

What is DNA and why is it important?

• DNA is the genetic blueprint found in cells—blood, skin, bone, etc.—containing 46 chromosomes (23 from each parent).
• Only ~0.3% of the DNA (about 3 million base pairs) differs among individuals, but these small differences form the basis of unique identities.
• DNA fingerprinting uses these differences to establish identity, paternity, and ancestry.

What are DNA polymorphisms?

• Polymorphism means variations in DNA sequences among individuals.
• These are often found in the non-coding regions of DNA.
• The most used polymorphisms for identity testing are Short Tandem Repeats (STRs)—repeating units of 2-6 base pairs.

Understanding STRs and DNA Fingerprints

• DNA has two strands composed of four bases: A, T, C, and G.
• STRs are sections where a short DNA sequence repeats.
• The number of repeats varies between individuals, creating a unique pattern.
• DNA fingerprinting uses these unique repeat patterns to differentiate individuals.

How are DNA profiles generated?

• Scientists use Polymerase Chain Reaction (PCR) to amplify the STR regions.
• Capillary electrophoresis separates DNA fragments based on size.
• STRs from multiple sites are analyzed simultaneously to ensure accuracy.

What is a DNA fingerprint?

• It is a unique set of STRs obtained from an individual’s DNA.
• Each person (except identical twins) has a distinct DNA fingerprint.
• It can be obtained from saliva, blood, hair, skin, semen, teeth, bones, etc.

Applications of DNA Polymorphism and Fingerprinting

• Criminal investigation: Identify suspects or exonerate the innocent.
• Disaster victim identification: Use remains to identify victims.
• Paternity/ancestry tests: Confirm familial relationships.
• Archaeology: DNA from ancient remains (e.g., 65,000-year-old samples) used for lineage tracing.

Conclusion

DNA fingerprinting using STR polymorphisms has revolutionized forensic science, legal identification, and ancestral research. It is a precise, reliable, and widely accepted method due to its uniqueness to individuals and resilience across generations and environments.

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