News: Authorities are using DNA analysis to identify the remains of those killed in the Air India Boeing 787 Dreamliner crash in Ahmedabad. DNA Identification
About DNA Identification
- DNA identification is a scientific method used to identify an individual based on their unique genetic makeup by comparing their DNA with DNA found in biological samples such as blood, hair, or tissue, to determine if they are the source of the sample.
- Every person has a unique DNA that is present in nearly every cell of their body, with the exception of identical twins.
- Use: 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.
Collecting and Storing Samples
- DNA survives much better in cold and dry conditions, than when it is hot and humid.
- This is why samples have to be collected as soon as possible, and once collected, 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.
- DNA from soft tissues degrades much faster than that from hard tissues (bones and teeth).
- To identify who the collected DNA belongs to, 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 other’s DNA.
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.
- The STRs are typically found on nuclear DNA which is located within the nucleus of a cell.
- Mitochondrial DNA (mtDNA) analysis: This method is used when nuclear DNA is degraded or unavailable.
- Mitochondrial DNA is found within the cell’s energy-producing organelles known as mitochondria.
- As mtDNA is present in multiple copies within the cell, it is easier to recover from human remains that are not well preserved.
- This is used for identification because mtDNA is passed down by the mother, unchanged, to all her children.
- 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
- 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.
- 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, e.g. victim’s personal belongings such as a toothbrush and hairbrush.
- This method is not as effective as STR analysis.
