Decoding DNA: Forensic Genetics and the Evolution of Criminal Investigations

Author: Ekta Kumari, SEM VI, B. Sc - M. Sc Forensic Science (Integrated), National Forensic Sciences University, Gandhinagar

DNA is the most potential and accurate source of identification and plays a crucial role in forensic investigations. A cell contains 2 types of DNA i.e.it can be either nuclear DNA (inherited from both the parents) or Mitochondrial DNA (inherited from mother only) and based on the quantity and source of evidence it is determined which DNA should be extracted for further analysis. Like for example, if hair is found on the crime scene as trace evidence, if the root part of hair is present then nuclear DNA can be evaluated and if only the shaft of hair is present then mitochondrial DNA should be evaluated.

Sequence polymorphism plays a major role in analysis of DNA samples which can be achieved through the repetitive DNA sequences which can be either interspersed repetitive DNA sequences or tandem repeats. Interspersed repetitive DNA sequences can be present anywhere on the chromosome and tandem repeats are the sequences present next to each other (in tandem) and on the basis of size of this tandem repeats they are further classified into [1] satellite DNA (1000s of nucleotides), [2] minisatellites or VNTRs (10 – 100 basepairs ) and micro-satellites or STRs (2 – 10 basepairs).

STR Typing – STR typing is used evaluate specific regions in nuclear DNA, it is visualized as a game changer in forensic science as they have high discrimination power. According to a 2023 study, STR DNA analysis can be used to analyse coffee cups which could lead to new path in forensic investigations.

SNPs – single nucleotide polymorphism includes analysis of small stretches of DNA containing hyper variable regions. They are helpful in degraded DNA examination and is also considered as future of forensics. 

Y chromosome analysis – Y chromosome and mtDNA are called as “lineage markers”. These are helpful in cases of sexual assault evidence, paternity testing, verification of amelogenin Y-deficient males, human migration and genealogical research. In August 2023, Penn State University and other scientists published the first full sequence of human Y chromosome, which includes gaps in over 50% of the chromosome’s length and it also reveals genomic features that may affect fertility. 

X chromosome analysis - it helps in studying genetic variations in X chromosomes. A study in 2021 revealed that normal development requires one X chromosome to be inactivated, and that protein clusters alter the X chromosome’s structure and this knowledge leads to cures of genetic disorders.

Proteomics – it is the study of entire set of proteins present in biological sample, it helps to identify proteins, generates profiles of entire proteomes, measure protein homeostasis and how proteins adapt to external factors. Advanced proteomic technologies include:

  I. Electrospray ionization liquid chromatography tandem mass spectroscopy (ESI-LC-MS)

 II. Matrix assisted laser desorption ionization time of flight (MALDI-TOF)

 III. Surface enhanced laser desorption ionization time of flight (SELDI-TOF) etc. 

The applications of proteomics in forensic investigations are Protein biomarkers for identifying body fluids, determining time and cause of death, postmortem changes in tissues, detection and quantification of drugs and poisons, drug protein interactions. 

Single cell genomics – it is the study of genetic information of individual cells. Radars are new type of systems in single cell genomics that introduce a sensor into a cell that is complementary to a particular gene of interest. When the gene turns on, it hybridizes to the sensor, which leads to the expression of a payload protein. This allows cells to be turned into programmable machines that can produce a specific output when they sense specific input. 

DNA Database – all the analysis and advancements are possible majorly due to the existence of DNA Databases. DNA Database is a collection of genetic information from individuals. Due to the evolution of AI in every sector, machine learning is also introduced in DNA Databases for faster and accurate analysis. 

Thus DNA evidence is easy to obtain because genetic material is found in all human cells, except red blood cells. As a result, when we leave behind small biological bits of ourselves, these bits can be used to identify us and link us to the places we've been.

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