Background of Gel Electrophoresis
Gel Electrophoresis is a technique used to separate molecules by their size and electric charge. It can be used to separate different lengths of DNA. The DNA is separated into fragments that can be separated in a gel on the basis of the size and electric charge. The medium used is a called Agarose gel which is made from purified seaweed. The reason the DNA moves due to its charge is because the phosphate head is negatively charged. It is used in forensic sciences due to the ability to isolate and compare small strands of DNA and other inorganic and organic substances found at crime scenes such as gunshot residues and blood proteins.
The DNA has to be fragmented to different sizes so the smaller molecules travel at faster speeds, occurring due to the smaller molecules able to pass through the pores in the gel faster. This can be done using Restriction Enzymes. These can recognise and cut DNA at a particular sequence of nucleotides
The Process of Gel Electrophoresis
Wells are created in the Agarose gel, and after being dyed, a sample of the DNA material is inserted into this well. The dye is to make it easier to see and record results. An electric current is run from the end of the gel where the samples are to the other end causing the samples to move through the medium. The dyes stain the gel showing how far along the molecules has moved, with the smallest molecules having moved furthest. Markers can be placed in the gel if you need to compare your sample with a known sample of DNA. A fluorescent light box can be used to locate the DNA samples in the Agarose gel. Comparing the DNA fragments of a suspect and of material found at a crime scene is how suspects can be convicted or acquitted. DNA profiling compares the two samples and if the bars on each sample match then the two samples are the same.
The Uses of Gel Electrophoresis
Gel Electrophoresis was as recently as 1995 for blood protein analysis in the trial of O.J. Simpson. Comparisons between his blood and the blood found at a crime scene. This was highly incriminating as the probability of the two samples being the same was 0.44%. Though the case was dismissed due to doubt in the jury about whether the FBI had tampered with evidence, it showed the process could be used to a fine detail. Now due to the DNA databases available the use of Gel Electrophoresis to isolate and compare DNA has become easier. As far back as 1987 DNA was used to link someone to a crime scene.
Currently research is being carried out to fulfill the job of Gel Electrophoresis in the field using a microchip and DNA reader. This would take much less time than carrying out the full process, yet a viable method has not been created yet. Another being worked on is a way to reverse to the electric current, allowing for separation of molecules several millions of base pairs long, thus removing the need to shorten the strands making the full process quicker.
