Context: After the Air India Boeing 787 Dreamliner crash in Ahmedabad, Gujarat, the authorities are using DNA analysis to identify the remains of those killed in the accident.
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.
Relevance of the Topic:Prelims: DNA Profiling: Challenges & Methods; Applications of DNA Profiling.
What is DNA Profiling?
- DNA profiling is the technique used to identify individuals by analysing the unique patterns in their DNA.
- With the exception of identical twins, every person has a unique DNA that is present in nearly every cell of their body.
DNA Identification: Sample Collection & Analysis
- DNA samples have to be collected as soon as possible from the body. As soon as an individual dies, their DNA begins to degrade.
- Extent of degradation depends on the kind of tissue DNA is extracted from, and the conditions in which the body is kept.
- DNA from soft tissues degrades much faster than that from hard tissues (bones and teeth).
- Collected samples need to be 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.
- For identification of the collected DNA sample, reference samples are collected from biological relatives. Parents and children of the victim are ideal candidates for providing these samples, given that they share 50% of each others’ DNA.
Methods of DNA Analysis
After the samples are collected, the next step is to extract DNA from them. Depending on the quality of the collected DNA, scientists can choose between a number of different methods of analysis.
Short Tandem Repeat (STR) Analysis:
- The method evaluates short tandem repeats, which are essentially short repeating sequences of DNA. STRs are used for DNA identification as they widely vary between individuals.
- STRs are typically found on nuclear DNA which is located within the nucleus of a cell. Therefore, to carry out STR analysis it is essential that the nuclear DNA extracted from the sample is not degraded.
Mitochondrial DNA (mtDNA) Analysis:
- This method is used when nuclear DNA is degraded or unavailable.
- mtDNA is found in mitochondria, the cell’s energy-producing organelles. As mtDNA is present in multiple copies within the cell, it is easier to recover from human remains that are not well preserved.
- mtDNA is passed down by the mother ‘unchanged’ to all her children. The samples can be matched with reference samples from their mother, maternal grandmother, siblings, maternal aunts or distant relatives from the maternal line of inheritance.
Y chromosome Analysis:
- Humans have two types of sex chromosomes, X and Y: biological males typically have one X and one Y chromosome, and biological females typically have two X chromosomes.
- In this method, a panel of STR on Y chromosomes, passed on from father to son, is examined to match the remains of the victim with their male relatives.
- Any member of the paternal line, including brothers, paternal uncles, and paternal male cousins, may be used for matching.
Single Nucleotide Polymorphisms (SNPs) Analysis:
- The method is typically used when the DNA to be analysed is highly degraded.
- A SNP is a variation in the DNA sequence where a single base (A, C, G, or T) at a specific location differs among people.
- Given that SNPs are unique to each person, they can be used for identification purposes with the help of reference samples taken from the victim’s personal belongings (E.g., a toothbrush and hairbrush). This method is not as effective as STR analysis.
Also Read: DNA Profling