How DNA Identification Works?

Syllabus: GS3/Science and Technology

Context

• After the Air India Boeing 787 Dreamliner crash in Ahmedabad, authorities are using DNA analysis to identify the remains of those killed in the accident. 

About

• With the exception of identical twins, every person has a unique DNA that is present in nearly every cell of their body. 
• DNA identification is the gold standard for identifying human remains, especially after mass fatality events in which bodies might not be easy to identify otherwise.

Challenges in DNA Identification

• DNA Degradation: It begins immediately after death and affects analysis accuracy.
• Factors Impacting Degradation:
  • Tissue type: Soft tissues degrade faster than hard tissues (bones, teeth).
  • Environmental conditions: DNA survives better in cold and dry conditions than in hot and humid ones.
  • Sample Collection Timeline: Delays can further degrade DNA.

Preservation of DNA Samples

• Samples have to be collected as soon as possible, and once collected, stored in a cool and dry environment. 
• They should ideally be frozen at minus 20 degrees Celsius, or, in the case of soft tissues (skin, muscles, etc.), they may be stored in 95% ethanol.

Methods of DNA Analysis

• Reference DNA is needed to match unidentified remains.
  • Ideal sources: Parents and children (share 50% of DNA).
  • Other possible sources: Maternal or paternal relatives depending on the method used.
• Depending on the quality of the collected DNA, scientists can choose between a number of different methods of analysis.
• Short Tandem Repeat (STR) Analysis: Its basis is the short repeating DNA sequences.
  • STRs are typically found on nuclear DNA which is located within the nucleus of a cell.
  • Use: High variability among individuals makes STR ideal for identification.
  • Limitation: Requires well-preserved nuclear DNA.
• Mitochondrial DNA (mtDNA) Analysis: Found in mitochondria (outside the nucleus), this method is used when nuclear DNA is degraded or unavailable.
  • mtDNA is passed down by the mother, unchanged, to all her children. This means that samples from a person’s remains can be matched with the maternal line of inheritance.
  • Advantage: Easier to recover from degraded samples due to multiple copies per cell.
• Y-Chromosome STR Analysis: Analyses STRs on the Y chromosome.
  • Inheritance: Passed from father to son.
  • Application: Matches possible with any paternal line male relative (e.g., father, brother, paternal uncle).
• Single Nucleotide Polymorphism (SNP) Analysis: It is based on the variation at a single base (A, C, G, T).
  • It is applied when DNA is highly degraded.
  • Sources for reference: Victim’s personal items like toothbrushes or hairbrushes.
  • Limitation: Less effective than STR analysis.

Conclusion

• DNA identification is a critical tool in disaster victim identification. Each method has strengths and limitations based on the quality of DNA, type of tissue, and available reference material. 
• The choice of method depends on the condition of remains and availability of relatives or personal items.

Source: IE