How DNA Fingerprinting Can Detect Criminals

DNA fingerprinting involves the usage of genetic information for human identification. DNA fingerprinting is a very important tool in forensics, as DNA is unique among all individuals (with the exception of identical twins). But this process is faced with certain controversies, such as generating a high probability, population genetics and technical difficulties. How DNA Fingerprinting Can Detect Criminals Every human, animal and plant is said to have a characteristic phenotype or physical appearance. This is because each of these organisms possesses a unique hereditary composition.

With the exception of identical twins, which share the same genotype but have subtly different phenotypes, no two persons have matching genetic makeup. The principle of identical uniqueness is the premise behind the usage of DNA for criminal detection (Kirby, 1993). What is DNA Fingerprinting? DNA fingerprinting (also known as DNA typing) is a form of identification that involves the comparison of deoxyribonucleic acid (DNA) fragments (MSN Encarta, 2008). The chemical structure of DNA among all living beings is the same.

However, the order of the base pairs is different. Every person has a different sequence of DNA base pairs (Brinton and Lieberman, n. d. ). As there millions of base pairs in a person’s DNA, the task of identification solely by the sequence of DNA base pairs is very time-consuming. Scientists instead use a shorter alternative, one that analyzes repeating patterns in DNA. Although these patterns do not give an individual fingerprint, they are able to find out whether two DNA samples were taken from non-related people, the same person or related people.

Scientists get a certain probability of a match by studying a small number of DNA sequences that have a high level of variation among individuals (Brinton and Lieberman, n. d. ). History of DNA Fingerprinting English geneticist Alec Jeffreys first described DNA fingerprinting in 1985. His studies revealed that human DNA contained certain regions wherein DNA sequences underwent constant duplication. In addition, the number of repeated sections in a DNA sample varies from one person to another.

Jeffreys was able to carry out human identity tests by devising a procedure in which the length variation of DNA repeat sequences were examined (President’s DNA Initiative, n. d. ). The repeated sections in a DNA sample was referred to as variable number tandem repeats (VNTR). The technique that Jeffreys devised was called restriction fragment length polymorphism (RFLP) – a restriction enzyme was used to cleave DNA regions surrounding the VNTR. The first cases in which RFLP was used were a double homicide case and an English immigration case. The usage of DNA typing methods in human identity testing has been widespread ever since.

In the United States, at least 150 public forensic laboratories conduct numerous DNA tests every year (President’s DNA Initiative, n. d. ). How is DNA Fingerprinting Done? DNA fingerprinting is made up of the following processes: performing a Southern Blot, making a radioactive probe, creating a hybridization reaction and the VNTR (Brinton and Lieberman, n. d. ). Performing a Southern Blot. The Southern Blot involves the analysis of genetic patterns that may be present in a person’s DNA. It is composed of the following steps: 1. Isolating the DNA in question from the rest of the cellular material in the nucleus.

This procedure can be done either chemically (using a detergent) or manually (applying a huge amount of pressure). 2. Cutting the DNA into several pieces of different sizes through one or more restriction enzymes. 3. Sorting the DNA pieces by size. 4. Denaturing the DNA (to render it single-stranded) 5. Blotting the DNA. (n. pag. ) Making a Radioactive Probe. Below are the necessary steps in making a radioactive probe: 1. Radiolabeling DNA polymerase (turning DNA polymerase radioactive). 2. Introduction of nicks or horizontal breaks along the DNA strand that is to be radiolabeled.

3. Adding DNA polymerase with the nicked DNA strand. 4. The DNA polymerase’s repair of the nicked DNA. 5. Heating the nicked DNA in order to produce single-stranded radioactive and non-radioactive pieces. (n. pag. ). Creating a Hybridization Reaction. Below are the procedures involved in creating a hybridization reaction: 1. The binding of two genetic sequences. 2. Denaturing of DNA by heat or chemicals. 3. Matching of denatured DNA with a single-stranded radioactive probe. 4. The adhesion of sequences of varying homology to the DNA. (n. pag. ) VNTR.