How DNA Identification Works?

Brief Context

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.

Source Content

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