The definition of DNA
Deoxyribonucleic acid (DNA) is a nucleic acid consisting of genetic instructions needed by all living organisms to function and develop. The only exceptions are the RNA viruses being the exception (Ghosh & Bansal 2003, p. 621).
A brief history about the discovery of DNA
The history of the discovery of DNA dates back to 1865 when Gregory Mendel used theories of heredity in analyzing the genetic profiles of pea plants. Genetic science came into being in 1900 following the discovery of Mendel’s work by Erich Von Tsechrmark, Carl Correns, and Hugo DeVries. In 1935, Nikolaevitch Belozersky succeeded in his quest to isolate DNA. In 1953, Francis Crick and James Watson proposed the complementary, helical, anti-parallel and double-stranded model of DNA (Dahm 2008). DNA polymerase was discovered and isolated by Coenberg in 1958. In 1966, Marshall Nirenberg, Severo Ochoa and Heinrich Mathei demonstrated that each of the 20 amino acids can be determined by a three nucleotide bases sequence, a move that proved useful in cracking the genetic code.
The first DNA cloning trial was successfully undertaken in California, in 1972. A year later, the first recombinant DNA organism was produced. Four years later, the NIH released guidelines for the first recombinant DNA. The guidelines sought to restrict different types of experiments. In 1980, Kary Mullis, together with his fellow scientists at the Berkeley-based Cetus Corporation, invented the PCR (polymerase chain reaction). The PCR technique allows for in vitro multiplication of DNA sequences. In 1984, Alec Jeffreys was instrumental in helping to introduce the DNA fingerprinting technique. The technique has proved quite useful in the identification of individuals. The technique was used in a court of law for the first time in 1985. The National Center for Human Genome Research was created in 1989, with James Watson as its head. The organization was charged with the responsibility of overseeing the $ 3 billion set aside by the U. S. government to facilitate in human DNA sequencing by 2005.
The Human Genome Project was launched in 1990, at an estimated cost of $ 13 billion. The launch was an international effort aimed at mapping the human genome (Prophase Genetics, 2006). This would facilitate in better and faster identification of U.S. soldier who dies while in combat. In 1993, a map of the human chromosomes (the 23 pairs) was produced by the Daniel Cohen led international research team ( Maddox, 2003). In 1995, DNA fingerprinting and PCR technology were used in a high-profile murder trial case involving O. J. Simpson, a former football player. Using the new techniques, the courts found O. J. Simpson not guilty. In 1997, Dolly the sheep was cloned by researchers from the Roslin Institute in Scotland. Shortly thereafter, Polly was cloned. In 1998, the human genome map appears, albeit as a rough draft. The map reveals over 30,000 gene locations. In 2000, after a decade-long effort, the human genetic code is finally cracked by scientists. This milestone could potentially revolutionise disease diagnosis and treatment of hitherto incurable diseases.
How can DNA be extracted & PCR
The extraction of DNA occurs routinely whenever it is necessary to collect DNA to undertake forensic or molecular analysis. DNA extraction process consists of some basic steps. First, the cells have to be opened up so that the DNA is exposed. This is the cell lysis or cell disruption step. To achieve this, the sample is either sonicated or ground. Next, a detergent is added to the ground sample to facilitate in the removal of membrane lipids. Thereafter, a protease is added to remove the proteins. Adding RNase helps to remove RNA. Next, the DNA is precipitated with an alcohol, either in the form of isopropanol, or an ice-cold ethanol. DNA does not dissolve in alcohols and after centrifugation it aggregates, forming a pellet (Rice, 2010). The alcohol-soluble salts are also removed during this step. A chelating agent can be added to help sequester such divalent cations as Ca2+ and Mg2+. Consequently, the DNA cannot be degraded by the DNase enzyme.
PCR
PCR (polymerase chain reaction) is a technique that helps to amplify a piece of few copies of DNA to generate numerous copies of specific DNA sequence (Saiki et al 1985). Examples include sequencing of DNA for cloning, functional genetic analysis, and DNA-based phylogeny (Saiki et al 1988).
How does DNA different from one person to another
DNA differs from one individual to another, even among monozygotic twins. This is because of the process of mutation observed during the process of gene copy number variation development (Bluder et al. 2008, p. 764). Such techniques as genetic fingerprinting rely on differences between individuals.
DNA linkage in crime
Forensic scientists use blood, skin, saliva, semen, or hair samples while investigating crimes. These samples are likely to be found at the scene of crime and are therefore helpful in identifying the DNA of an individual, in this case, the perpetrator of a crime (Turvey 2008, p. 354). The process is referred to as genetic fingerprinting or DNA profiling.
Advantages of using the DNA analysis
DNA analysis is highly reliable compared with the testimony of eye witnesses. Based on the frequency of the patterns of comparison, there is a1/7000 to 1/1,000,000,000 chance of finding matching DNA between two individuals (Klug & Cummings 2007, p. 87). Also, every small sample sizes of say 10 microliters could be enough for DNA analysis because using the PCR technique, one can amplify the DNA.
Case discussion supporting one of the advantages
Suppose the only item available to exonerate a suspect to a rape for example, is a very minute hair strand found at the crime scene. Using PCR technique, forensic scientist can amplify the DNA millions of time and if it matches the suspect, then this evidence can be presented at the courts to incarcerate him/her.
Disadvantages of using DNA analysis
A consensus has not been reached on what to do with the collected DNA samples. For example, police may use it in the future to solve crimes. DNA analysis may also lead to an overrepresentation of minorities in the DNA bank, at the expense of the majority (Butler 2005).
Cases support miscarriage of justice by discussing one of the disadvantages
The high rate at which minorities are arrested means that DNA samples are taken from this group more than any other group. Consequently, the DNA bank over-represents the minorities. Since the police are more likely to focus their investigation on areas where there is a DNA match, as opposed to investigating all crimes, minorities are more likely to be faced with higher rates of conviction.
The evolution and growth in DNA technology “machines and databases”
Over the years, DNA technology has evolved and today, machines and databases are used to store the DNA profiles of crime suspects. In future, should the same victim commit another crime, the ensuing profile can be compared with that which has already been stored in the DNA database (Huffine 2008, p. 24). If there is a match, then there is enough evidence to convict the suspect. Hypothetically, this may also act as a crime deterrent strategy for incarcerated convicts. The use of the DNA databases also helps to speed up processing of DNA analysis, thereby reducing case backlogs.
Ways of improving the usage of DNA in crime scene analysis and more ways of using DNA fingerprint
DNA databases facilitate the exchange and storage of DNA profiles at the local, state and national levels through the CODIS (Combined DNA Index System) technique. This ensures that DNA profiles that have been obtained at the local, state, and federal systems are maintained in databases that the law enforcement agencies can access to assist in enforcing the law (Butler, 2005). DNA technology can be improved in a number of ways. For example the use of nanotechnology to develop a “DNA chip technology” to enhance resolution and speed in DNA evidence analysis. In addition, the use of such advanced DNA analysis techniques as mitochondrial DNA analysis and Short Tandem Repeats is yet another way of improving DNA technology.
Reference List
Bruder, C., et al., 2008. Phenotypically Concordant and Discordant Monozygotic Twins Display Different DNA Copy-Number-Variation Profiles. Am J Hum Genet, Vol. 82, No. 3, pp. 763–771.
Butler, J.M., 2005, Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers (2nd Edition). New York: Elsevier Academic Press.
Dahm, R., 2008. Discovering DNA: Friedrich Miescher and the early years of nucleic acid research. Hum. Genet, Vol. 122, No. 6, pp. 565–81.
Ghosh, A., & Bansal, M., 2003. A glossary of DNA structures from A to Z. Acta Crystallogr, Vol. 59, No. 4, pp. 620–6.
Huffine, E., 2008. International Impact of Forensic DNA Technology. Forensic Magazine, Vol. 5, No. 5, pp. 23-28
Klug, W., & Cummings, M., 2007, Essential of Genetics. 6th ed. Upper Saddle River, NJ: Prentice Hall.
Maddox, B., 2003. The double helix and the ‘wronged heroine’. Nature, Vol. 421, No. 6921, pp. 407- 408.
Prophase Genetics., 2006. History of DNA. Web.
Rice, G., 2010. DNA Extraction. Web.
Saiki, R., Scharf, S., Faloona, F., Mullis, K.,Horn, G., Erlich, H., & Arnheim, N., 1985. Enzymatic amplification of beta-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anemia. Science, Vol. 230, No. 4732, pp. 1350- 1354.
Saiki, R., Gelfand, D., Stoffel, S., Scharf, S., Higuchi, R., Horn, G., Mullis, K., & Erlich, H.,1988. Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science, Vol. 239, No. 4839, pp. 487- 491.
Turvey, B. E., 2008, Criminal profiling: an introduction to behavioral evidence analysis. Waltham, Mass: Academic Press