DNA: Its contribution to the forensic sciences
Forensic science, DNA, DNA profiling, STR, PCR, mDNA, criminology
We begin life as a single cell zygote, about 0.1mm in diameter. The numerous biological instructions that enable our developmental and functional processes to occur from zygote to adult are encoded in the deoxyribonucleic acid (DNA). Forensic DNA analysis involves the intersection of several scientific disciplines, including molecular biology, genetics, and statistical analysis (Lynch, 2013). In order to understand the usefulness and the limitations of DNA in the analysis of physical evidence, it is important to be familiar with the basics principles underlying these diverse disciplines. Besides identical twins, each individual’s DNA is unique. After all it is the genetic material that contains all the information necessary for any organism to develop and function. However, only a one-half percent that is of interest to forensics scientists. This is the portion that varies greatly between individuals and it is what manifests itself in the individual traits such as eye color, hair color, and blood type. Most often the differences in DNA sequence do not show themselves in physical appearance; however, these sequences can only be examined using special laboratory techniques. Forensic scientists use these genetic differences from DNA to distinguish an individual between the individuals in a population. In 1944 Oswald Avery defined the role of the cellular component known as DNA as the vehicle of generational transference of heritable traits. In 1953, James Watson and Francis Crick elucidated the structure of the DNA molecule as a double helix. Form follows function; the very nature of the molecule provided an explanation for its unique properties (Berg, Tymoczko, Stryer, Gatto & Gatto, 2012). In 1980, David Botstein and coworkers were the first to exploit the small variations found between people at the genetic level as landmarks to construct a human gene map. In 1984, while searching for disease markers in DNA Alec Jeffreys discovered the science of personal identification. He termed this method DNA Fingerprinting, a method to detect loci sequentially (Alberts, Johnson & et al, 2008). This term is later replaced by DNA typing or DNA profiling, “Early in the use of DNA, profiles for the purpose of identification were called DNA fingerprints, a term which is now rarely used” (Porter, 2005). The first forensic use of DNA occurred in England, “… a DNA test was performed by Dr. Alex Jeffreys, who had developed DNA ‘fingerprinting” (Porter, 2005). One of the most significant facts of the case is that an innocent suspect was the first accused of the murder was freed based on the DNA evidence. Perhaps the most significant scientific advance besides the determination of the structure of DNA was in 1986 the polymerase chain reaction (PCR). PCR multiplies the sample and yields results which were once unobtainable, “Furthermore, the statistical chances of a random coincidence in DNA of two individuals with the same profile have now reached enormous figures in the billions (Porter, 2005). Observation of cells and embryos in the late 19th century had led to the recognition that the hereditary information is carried on chromosomes, “thread-like structures in the nucleus of a eukaryotic cell that became visible by light microscopy as the cell begins to divide” (Alberts, Johnson & et al, 2008). As biochemical analysis became possible, chromosomes were found to consist of both DNA and protein. DNA is the name given to a group of molecules that occur in all cells of all living organisms and that carry that organism’s genetic information. That, is they carry the instructions for making the chemical compounds, proteins, by which cells stay alive, grow, develop, reproduce, and carry out all the functions that constitute life as we know it. DNA molecules are very large, complex molecules made of...
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