What's the biggest challenge in DNA analysis?
How do DNA samples help?
DNA fingerprinting identifies individuals by analysing unique regions of their DNA. While human DNA is 99.9% identical, the remaining 0.1% includes unique sequences called short tandem repeats (STRs), which are crucial for forensic investigations. DNA profiling focuses on specific regions called genetic markers, with STRs being the preferred markers due to their variability among individuals, except monozygotic twins (identical twins).
'Currently, STRs are the most widely used genetic markers for human identity determination and paternity testing. Their use makes it possible to clarify most legal and forensic cases with a generally very high degree of certainty. Identification of human remains is generally performed by comparing the genetic profile of the remains with that of first-degree relatives, usually the parents,' explained Dr. Rakesh Mishra, director, Tata Institute for Genetics and Society.
DNA is the molecule that carries the genetic instructions of all living organisms. It's essentially the blueprint that determines an organism's characteristics and how it functions and is passed from parents to offspring. DNA profiling can be used in the identification of skeletonised or highly decomposed human remains. Identification is usually carried out by comparing the genetic profile from the remains with the genotypes of reference samples from relatives, most commonly the parents of the victim, according to an article titled, 'Identification of the Remains of an Adult Using DNA from Their Deciduous Teeth as a Reference Sample'.
What is the process followed to collect, store and match samples during a disaster?
In the case of accident victims, DNA samples may be degraded and contaminated which is the biggest challenge that forensic experts face even though DNA samples can be preserved for a long time. Samples are ideally frozen at minus 20°C, or, in the case of soft tissues (skin, muscles, etc.), they may be stored in 95% ethanol.
'In an accident of this magnitude samples of tissue, nails, bone, body fluid and blood etc. can be used to identify and establish family relation. Technology available today is powerful and sensitive which aids in easy identification,' said Dr. Mishra. He added that only trained forensic experts are made to collect samples to ensure that there is no contamination. These samples are then stored in temperature regulated, sterile conditions and matched swiftly.
'In this case, establishing family pattern is enough. The STR process is used in this case to establish family relationship. Through this family pattern is established and based on this identity is ascertained,' he said.
Experts noted that after sample collection, using Polymerase Chain Reaction (PCR) the extracted DNA is amplified with specific primers targeting the STR regions of interest. The amplified DNA fragments are separated based on size using gel electrophoresis. The size and number of repeats in each band are analysed to generate the distinctive DNA profile with advanced computerised systems. The generated profile is then compared to other DNA profiles in a database to find any matches.
What are the difficulties in the process?
An article titled, 'Challenges and solutions in DNA fingerprinting: Sample quality, data analysis, and interpretation', noted that DNA fingerprinting, which is a pivotal tool in forensic science, paternity testing, and genetic research, faces significant challenges in sample quality, data analysis, and interpretation. It states that the sample quality is the bedrock of DNA fingerprinting. 'The integrity of the DNA sample dictates the accuracy of the result. Challenges arise from various sources, such as environmental degradation, contamination, and the complexity of handling mixed or limited DNA samples. These issues can lead to ambiguous or erroneous results, posing significant obstacles in forensic investigations,' it states. It adds that continued training and education of those in the field is vital.
Contamination, interpretation challenges, including ethical concerns, privacy issues, and the potential for misinterpretation of results is acknowledged in this paper. It recommends the use of advanced techniques for DNA collection and recovery, developments in software for more precise data analysis, and the implementation of standardised protocols for interpretation. It also highlights the role of automation in enhancing accuracy and the importance of professional training.
When has DNA fingerprinting been crucial?
Several mass fatality events, including natural disasters and terrorist attacks, have forced authorities to use DNA analysis to establish identity. Most recent include the 2004 Indian Ocean tsunami, the 2009 Victorian Bushfires (Australia) where severely burned or fragmented bodies had to be identified, and the 2014 MH17 crash (Ukraine) which resulted in the loss of all 298 people on board. DNA fingerprinting was also used to identify victims of the 9/11 terrorist attacks. Beside this, it is also a standard tool for identifying individuals in various criminal cases.
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