The Role of Molecular Biology in Identification of Human Bodies

Life is so unpredictable, and every day brings a new challenge for the human race. Along with lots of happiness and cheers, disasters and accidents are also the part and parcel of life. In case of massive disasters such as plane crash, massive fire accidents and marine accidents there is always a deep grief among the masses but the saddest part is that the people could not have access to the remains of their loved ones so that they can perform the funeral rituals according to their religion. But as in case of plane crash the identification of bodies is quite impossible due to high temperature and massive destruction. Usually the identification is carried out by the help of birthmarks, clothing, dental records, fingerprints and jewelry but in such cases when all these methods of identification are not applicable then molecular biology caters the emotional needs of people. DNA typing is the most authentic and sometimes the only available method for identification of human remains in mass casualty disasters. DNA (deoxyribonucleic acid) is a molecule that contains the complete genetic information of the organism and is unique to that organism. Besides its uniqueness according to Mendelian laws of inheritance an individual’s DNA is composed of 50% of its mother’s DNA and 50% of its father’s DNA.

Professor Alec John Jeffrey developed the techniques of DNA typing and DNA fingerprinting. The advantage of DNA testing is that the easily available sample such as, hair, bone, blood, saliva, buccal cells, nails, a small part of skin or flesh can be taken as sample. DNA is quite heat resistant and can also persist in very harsh environmental conditions.

For reference DNA sample can be taken from any biological sample (blood, bone-marrow, etc.) which was given previously and has been stored but it is commonly not available. The personal use items such as toothbrush, razors etc. can also be used for taking DNA sample as a reference. But mostly the reference sample is taken from biologically related persons such as father, mother, son, daughter or siblings. If unfortunately, any of the family member is not alive then biological aunts or uncles could be contacted for sample donation.

Different techniques of DNA typing are used in this regard. The commonly used techniques are:

1.  RFLP (Restriction Fragment Length Polymorphism)
2.   STR (Short Tandem Repeats)
3.   Mitochondrial DNA analysis
4.  Rapid DNA analysis

Prior to these techniques DNA extraction is carried out i.e., isolation of DNA from cell. Different methods are used such as, phenol-chloroform extraction, chelex method etc. In all these methods first of all the cellular and nuclear membranes are lysed using detergents and enzymes, then to separate DNA from cell debris precipitation is done and then the DNA is purified usually by washing with alcohol to remove any unwanted material. The phenol-chloroform method is commonly used in case of animal cells.

1. RFLP is the oldest technique in which extracted DNA is cut into short fragments using restriction endonucleases which results in varying length fragments in different individuals as a result of genetic variance. The fragments are then separated based on their size using gel electrophoresis, then these fragments are transferred to a nitrocellulose membrane and are fixed and then denatured. After that radioactive DNA probe is added for binding with specific fragments and the membrane is washed to remove the excess unbound probe. Then an X-ray film is used to detect the radioactive pattern and the results are analyzed. RFLP has almost become obsolete as it is a very long and laborious process and it also requires a large sample of DNA.

2. STR typing is a PCR based and the most employed method nowadays. Short Tandem Repeats (STRs) are nucleotides sequences with repeated motifs of variable lengths (2 to 8bp) that are polymorphic. Biologically irrelevant people have varying repeat units that is why this method can be used for identification and discrimination from other samples. The STR loci are mixed with sequence specific primers and then subjected to amplification via PCR. The amplified DNA is then analyzed and compared by gel electrophoresis. The DNA of related persons have similar pattern and in this way the process of identification can be completed.

3. Mitochondrial DNA analysis is applied when nuclear DNA sample is not available or has been degraded due to extreme heat or when the sample size is very small. Mitochondrial DNA is a small circular chain of DNA residing inside mitochondria. Each mitochondrion contains one copy of circular DNA. Since there are many mitochondria in each cell, a lot of mitochondrial DNA may be present in only a small sample of cells. The advantage of using this is the large available amount. But its profiling is not as authentic as of nuclear DNA and since it is inherited only from mother while nuclear DNA is inherited half from mother and half from father, therefore reference sample must be taken from a maternal relative only.

4. Rapid DNA is defined as a fully automated process of developing a Core short tandem repeat (STR) profile from a buccal swab. It is purely a non-invasive and hands-free method and includes extraction, amplification, separation and detection without any human intervention. The samples are loaded into the system and the results are obtained within two hours. The RapidHIT ID, and ANDE Rapid DNA identification system are commonly used and authentic systems. It is not a novel technique, it is typically a STR based method performed using most recent technology. It is the fastest available method but not has been common due to its higher cost.

DNA profiling is till now the best-known method for identification of human remains in forensics, but this was not so much widely accepted and employed before 2001. After 9/11 incident DNA profiling was carried out on a large scale for identification of deceased bodies. The research is continued to make it better, faster and cheaper.

References

1.  Turingan, R. S., Brown, J., Kaplun, L., Smith, J., Watson, J., Boyd, D. A., ... & Selden, R. F. (2019). Identification of human remains using Rapid DNA analysis. International journal of legal medicine, 1-10.
2. https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/dna-typing-0#:~:text=DNA%20typing%20is%20a%20laboratory,transplantation%20of%20organs%20and%20tissues. 
3. ICRC, M. P. (2009). DNA Analysis and Identification of Human Remains. A Guide for Best Practice in Armed Conflicts and Other Situations of Armed Violence,.

By: Mehwish Hamid