14th October 2012
"33 autorad off"
On 10th September 1984, geneticist Alec Jeffrey’s wrote these three words in his red desk diary. This marked the completion of an experiment, which studied how inherited illnesses pass through families. The experiment failed entirely. (McKie, 2009) However, this led to the most profound discovery: the world’s first DNA fingerprint. Now, the smallest swab of blood or sweat can determine the identity of an individual. We will discuss this process of DNA profiling in this journal. After going into the in-depth analysis of DNA profiling, we will discuss its uses and the ethical and legal issues that swarm the subject.
|What is DNA Profiling? |
Formally, DNA profiling is the analysis of short, highly specific, tandem-repeated- or hypervariable- genomic sequences, minisatellites known as variable number of tandem repeats (VNTRs), to detect the degree of relatedness to another sequence of oligonucleotides. (Segan, 1992) It is a technique employed by forensic scientists to assist in the identification of individuals by their respective DNA profiles, which are encrypted sets of numbers that reflect a person's DNA makeup and can also be used as the person's identifier.
|The Process |
Deoxyribonucleic Acid ("DNA") is a six-foot long molecule found in the nucleus of every cell in the body. With the exception of identical twins, each individual’s DNA is unique. Thus the first step in the profiling process is to obtain a sample of the individual’s DNA, which is usually done using a buccal swab (i.e. from the cheek). We could also use a sample of blood, semen or hair. This sample is then analyzed using different techniques; discussed below.
|Techniques of DNA Profiling | |Restriction Fragment Length Polymorphism (RFLP) |
It is a technique that exploits variations in homologous DNA sequences. It refers to a difference between samples of homologous DNA molecules that come from differing locations of restriction enzyme sites, and to a related laboratory technique by which these segments can be illustrated. In this process, the DNA is first chemically extracted from the sample. It is then fragmented using restriction enzymes. These enzymes act like scissors and cut the DNA where a specific sequence occurs. By gel electrophoresis, the DNA fragments are placed in a gel through which an electric current is passed. Owing to the negative charge of the DNA, the fragments migrate toward the positively charged pole of the gel. The DNA is then denatured and Southern blotting transfers the DNA fragments to a nylon membrane. A buffer solution is pulled through the gel and membrane and absorbed in paper towels. Hybridization, brought about by radioactive probe, shows only those fragments of interest from the polymorphic area of the DNA. Autoradiography is carried out next where the blot is placed in contact with a piece of x-ray film, where the radioactivity probe exposes the film and bands appear on the film where the probe has bound to the DNA. The results are then interpreted and in the case of a criminal investigation or civil case, it is matched against the suspect’s DNA profile, thus completing the process. (Hoeffel, 1990) This method is however very long-winded, cumbersome and the combination of all the above-mentioned steps could take about a month to complete. A large sample is required which makes it tougher. Hence other methods are adopted in recent times.
|Polymerase Chain Reaction...