Introduction

It has always been the main objective of forensic scientists and criminal investigators of being able to identify the origin of biological evidence eat the crime scene with certainty. DNA profiling allows the investigation of human biological material at its elemental level – the DNA molecule, that is located in every living cell within the biological system, which contains the genetic material that distinguishes an individual from others. DNA from a biological sample, such as semen, blood, or tissue, is extracted and analysed as part of the DNA profiling procedure. DNA Profiling stands out due to its exceptionally low probability of false positives. DNA Profiling evidence should be as credible as any other type of scientific evidence presented in court, provided that stringent laboratory standards are meticulously followed. Furthermore, it is obvious that DNA Profiling marks a significant advancement in science’s ability to determine if two body samples collected at separate times are from the same person.^[1]

Forensic identification becomes particularly challenging in cases of defragmented, decomposing, or burned bodies. Since nearly 0.1% of human DNA sequences are unique to each person and can be used for research, DNA analysis is essential for overcoming such circumstances. Human Genome Project (HGP), an extraordinarily massive collaborative scientific project in the world to sequence the human genome, states that just 1.5% of the human genome's DNA actually codes for proteins, with the majority being referred to as "junk DNA." Variable number tandem repeats (VNTRs) or minisatellites are specific repeating sequences that makes up a significant amount of junk DNA. An inheritable pattern known as "DNA fingerprints" was created in 1984 by geneticist Alec Jeffreys using these distinctive tandem repeats, and the technique is now widely known as DNA fingerprinting. One of the most ground-breaking discoveries of the 20th century which was the discovery of DNA fingerprinting, has been used predominantly in the forensic science for the identification of criminal suspects by using biological samples and also for medical uses, for example, detecting diseases that are inherited, finding suitable tissue donor for organ transplantation, linking kinship and blood relatives and so on. In this article, we highlight and discuss the different types of DNA fingerprinting/profiling techniques applied in forensic science. ^[2]

Relevance for the Law

DNA profiling has proven to be a noteworthy application to the criminal law because of the possibility that it offers of determining whether human biological samples such as blood, saliva, semen etc. discovered at the scene of a crime come from a person suspected of having committed the crime. This is especially vital when looking into sexual offences. A prominent feature of DNA profiling over more traditional tests, like serological tests for blood, is that the DNA profile obtained from the crime scene can be matched with the sample of a suspect which is tested with certainty. Whenever an assailant is injured or leaves any evidence at the scene of a crime (such as hair, saliva, etc.), the DNA profile has the capability to identify the person from his/her DNA extracted. It can also acquit the suspect. DNA profiling provides the possibility of identifying victims of `unidentified crimes' such as hit-run cases. Moreover, it can give a clear indication whether the same person is responsible for a series of crimes, such as serial killings. DNA profiling has also been used extensively for paternity testing. The application of such information is wide, varying from family-related disputes, to resolving the identity of the father of the a child in case of rape victims, to rights to social security benefits, to inheritance issues. It is also of major significance to governments seeking to confine immigration to family reunion categories. ^[1]

When it comes to collecting and handling evidence at the crime scenes, it is essential to bear in mind that proper care is taken for the samples collected, in manner of maintaining integrity of the crime scene, wearing face masks during investigation of the scene, as improper handling of the evidence can lead to serious consequences. In worse cases, cross-contamination leads to an extreme level of sample degradation and this can confuse or avert the final result of evidence for submission at court of law. ^[3] Four decades after the development of DNA fingerprinting, DNA analysis has remained a bridge to link suspects to evidence found at crime scene and to identify individuals during crimes and disasters. DNA profiling has also been used to diagnose hereditary disorders and diseases. ^[4]

An Overview of DNA

For many years, scientists debated over which molecule carried the instructions for life. The majority of scientists thought DNA was far too basic a chemical to play such a crucial part. Instead, scientists hypothesised that proteins' higher complexity and wider range of forms made them more likely to perform this crucial task. ^[5] After the infamous series of ground-breaking experiments conducted by Hershey and Chase in 1952, it was evident how important DNA was as the genetic material. In 1953, thanks to the work of James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin, on X-ray diffraction patterns, a significant contribution was made towards unravelling the double helical structure of DNA; a structure that enables it to carry biological information from generation to generation. ^[5]

As it is widely known, DNA is situated in the cell nucleus (nuclear DNA), but a fragment of DNA can also be found in the mitochondria (mitochondrial DNA or mtDNA). ^[6] Similar to fingerprints, everyone has a DNA signature that is unique and remains unchanged throughout their lives. DNA testing, broadly called DNA profiling, exploits the fact that, with the except the case of homozygous twins, the genetic material of a person is unique and is an omnipresent residue that trails us wherever we go. ^[7] The human genome project validated what forensic researchers already knew, that the noncoding sections of the genome contain, among other things, stretches of repetitive sequences . The single-locus satellites are located at a specific site of a particular human chromosome, while multi-locus satellite repeats or generally known as STRs, are spread throughout the entire genome. ^[8]

Forensic DNA Analysis

Forensic genetics has progressed owing to the analysis of human genetic variations. Alec Jeffreys's revelation of hypervariable polymorphisms in the human genome, also known as variable nucleotide tandem repeats (VNTRs) or minisatellites, provided the impetus to the use of multilocus probes for DNA fingerprinting. This proved for match probabilities to be so low that only mono-zygotic twins could in a sense, share DNA fingerprints. VNTRs are also the foundation of the restriction fragment length polymorphism (RFLP) method. However, this simple pattern match which is more resilient, technically unmanageable, requiring minute quantities of DNA led to the utilization of single locus probes (SLP) that analyse unique minisatellite species under harsher conditions. Polymerase chain Reaction (PCR) based methods on the other hand, were used to convey qualitative and quantitative issues in forensic samples as well as the length of time needed for SLP Analysis. Short tandem repeats (STRs) or a microsatellite consisting of short repeating motifs contained within a minute fragments are, however, proven more suited for PCR. ^[8]

It has been almost 40 years since Dr. Alec Jeffreys, an English geneticist, first introduced the concept of “DNA fingerprinting”, or DNA Typing (Profiling), as it is now known. Evett and Buckleton, however, pushed for a modification to DNA profiling that has gained widespread support. ^[9] DNA Profiling has improved the system’s sensitivity, reproducibility in terms of results, as well as computer database compatibility. It has also rapidly established itself as the global standard forensic DNA Technology for paternity testing and criminal casework. ^[10]

DNA Database - CODIS

The establishment of DNA databases is another significant advancement in DNA profiling. The introduction of a national database in the United States allowed forensic scientists to enter unmatched DNA evidence found at the crime scene into a computerised system in order to make DNA matches. ^[40]

The CODIS is an acronym for Combined DNA Index System. It was started and supported by the Federal Bureau of Investigation (FBI) in 1990, and has since served as the foundation of the US DNA database. It was designed to enable open access forensic DNA testing facilities to build searchable databases of authorised DNA profiles. The CODIS programme enables laboratories in the United States to share and compare data. Apart from that, it also includes a central database with all DNA profiles from all the user laboratories. The 13 CODIS locations are TH01, TPOX, CSF1PO, vWA, FGA, D3S1358, D5S818, D7S820, D13S317, D16S539, D8S1179, D18S51, and D21S11. ^[29] The United States maintains the largest DNA database in the world: The Combined DNA Index System, with over 60 million records as of 2007. ^[29] CODIS was established to draw comparison between a target DNA record against the DNA records contained in the database. The laboratories involved in the match exchange information to confirm the match and create coordination between two agencies after the CODIS software identifies a match in order to establish a probable cause to obtain an evidentiary DNA sample from the suspect, the forensic DNA record must match the DNA record in the database. This documentation can then be used by the law enforcement agency to obtain a court order authorizing the collection of a known biological reference sample from the offender. The known biological sample can undergo a DNA analysis in casework laboratory so that the results can be presented as evidence in court. ^[51] According to Machado & Silva (2019), it was concluded that around 69 countries at present employ national forensic DNA databases; others are being expanded or established in at least 34 additional countries. ^[52]

Discussion

DNA profiling is one of the biggest achievements of the late 20^th Century. The analysis of DNA from biological evidence, which was first used in a criminal case in 1987, has completely revolutionised how forensic investigations are carried out. In the three decades thereafter, DNA profiling techniques have made significant furtherance in respect of their sensitivity, speed, and power. ^[54] Various number of unique approaches have been developed in the rapidly expanding field of forensic genetics in order to enable the analysis of exigent forensic samples and to provide intelligence about the donor of the biological sample. ^[57] This article puts forth the development of DNA profiling to a systemized investigative technique for use at court of law which has, since 1980s led to conviction of thousands of criminals and to exonerate many wrongfully suspected or convicted individuals. ^[58] DNA Profiling on its own could not bring down the crime rate in any of the many countries, however it helps to add unwavering scientific value to the evidence and increases the credibility of the legal system.

Before any new procedure can be adopted in any accredited forensic laboratory, robust validation processes are required. In addition to this, selection of right DNA typing platforms that meet demands of sample size, coverage, cost and is accurate is also a fundamental requirement of forensic DNA applications. In the meantime, research in forensic science and improvement in forensic investigation continue to advance. ^[54] Even advance techniques like Next-Generation Sequencing has been employed to identify novel, and rare cancer mutations, detect familial cancer mutation carriers and allows greater insight obtained from biological evidence. For instance, challenges such as extremely degraded or DNA in low quantity can be overcome to increase recovery of informative profiles. ^[59] NGS provides deep coverage to extract genetic information from minute quantity of mtDNA samples found in less than idea condition. ^[60]

With modern technology, the amount of DNA needed for analysis can now be extracted from even a minute biological sample, which enables relevant authorities to match suspects to evidence found at the crime scene. However, even an absolute “match” is not sufficient for concrete testament of guilt since forensic science is largely rooted in probabilities. Additionally, concerns with delayed sample entries, and individual genetic rights pose challenges to DNA databases which are designed to simply the process of connecting past offenders to recent crimes. This hinders usefulness of the databases. Even though forensic science is inarguably vital to the modern justice system, its ethical implications and personal implications are still debated in the legal, law enforcement, and scientific communities. ^[27]

Conclusion

DNA is the genetic code that is located in each and every cell of within an individual’s body. Although only 99.9 percent of DNA sequences is similar in every person, it is the 0.1 percent of the DNA difference that is unique to the individual and the forensic scientists are interested in. Typically, forensic DNA analysis is carried out in following steps: Sample preparation, DNA extraction, DNA amplification, DNA quantitation, and DNA profile matching where the profile obtained from crime-scene evidence is either entered into DNA database for comparison or compared directly with that from the suspect to determine whether suspect contributed DNA to the crime scene or not. Forensic DNA analysis has played an increasingly crucial role in criminal justice system. But as the role expands, many social, legal and ethical concerns are also raised. Of these, prevention of unauthorized use of an individual’s DNA profile, is of paramount importance. ^[61] Apart from this, reliability and robustness of DNA testing itself is an important concern, since errors can occur during evidence collection, storage of the samples, DNA extraction, etc., which could lead to accusation of the wrong person. DNA extraction methods have become more and more effective with regard to obtaining purified DNA from crime-scene evidence. Time continues to work against forensic sample analysis. This is because DNA tends to degrade under certain environmental conditions, and it becomes difficult for it to retain its integrity over an indefinite time of storage.

The most common challenges often faced by forensic DNA laboratories include the demand for a) faster DNA results from b) a vast number of samples which are collected from c) an ever increasing spectrum of substrates by the law enforcement agencies. Some laboratories have chosen to go for fully-automated methods in extraction process in order to reduce backlog of cases. Compared with the time-consuming gold standard organic extraction method, standardized rapid DNA and automated methods often lack a certain quality of sensitivity and robustness to handle wide range of samples, especially if it concerns low quantity of DNA. However, laboratories are making informed choices in expansion of arsenal of methods in their forensic DNA toolbox. ^[62] It is worth noting that even though numerous scientific improvements are sure to come, current methods employed are reliable and valid.

As more is understood about the functioning of the human genome, aspects of its new knowledge will be adapted for use in forensic science. ^[53] The DNA analysis has been proven to be a crucial tool in solving cases in forensics, such as establishing custody of a child through paternity or maternity tests, identification of victims from crimes or disasters, or exoneration innocent people convicted to prison. ^[8] The authors have demonstrated some of the established and cutting-edge methods in this concise review for the reader. This article presents a literature review referring to the main studies on DNA Profiling and makes an overview of the evolution of this technology in the last years, highlighting the importance of molecular biology in forensic science.

This review also highlights some of the important DNA Profiling techniques and their developments in the rapidly expanding field of forensic science. It will be crucially important that researchers consider how to harness the innovations thus produced by the dynamic field in order to ensure their implementation in forensic investigations. Many more exciting scientific and technological advances are still to be explored, and there is no doubt that the future landscape of forensic DNA analysis will look quite different from the one we see today.

Conflict of Interest

The authors declare that there is no conflict of interest.

Source of Funding

None.