Essay What is the Polymerase Chain Reaction (PCR)

Advances in DNA technology has expanded greatly in the world of forensic science. In the past a vast number of crime scene evidence was not considered for analysis is now being tested. Trace DNA is more effective in this century when convicting a criminal than it was 20-30 years ago. Due to the consist improvement of DNA technology forensic scientist are able to put away criminals the correct way.

Why is PCR helpful to forensic scientists? PCR is helpful to forensic scientists because it copies small fragments of DNA fast. It can also match people with DNA even if you only have a little bit of it from a crime scene.

DNA is the genetic blueprint for life because it contains the instructions that oversee the development of an organism. Taking samples of DNA and analyzing them to determine if they come from the same individual is known as DNA profiling. Investigators gather items such as hair, saliva, semen and blood that could contain DNA from a crime scene. DNA profiling is also used in paternity testing, victim identification and evolution research. First, the collected DNA samples are isolated. Next, selected sequences from each DNA sample are replicated to produce a large sample of DNA fragments. Finally, the enlarged DNA samples are compared to other samples to determine whether the samples came from the same person or

PCR works by denaturing the double-stranded DNA and annealing the primers to the newly-made single-stranded DNA, leading to the extension/elongation of the DNA by a polymerase that attaches to the primer/DNA strand. The PCR reaction strums through a handful of temperature cycles to maximize each step and the amount of product.

However, fingerprint can be contaminated if investigators are not careful, in which could lead to false conclusion and could develop false leads. Further, professional criminals would often avoid contaminating their crime by wearing gloves to prevent leaving fingerprints. The introduction of DNA methods has helped provide viable evidence for investigators. This is because DNA can leave traces such as, saliva, hair sweat and dandruff just to name a few. The DNA testing has also been accepted by the courts due to its accuracy and value to support evidence. (Hess, Orthmann, Cho, 2013)

These strands give each any every person a unique genetic code, different from the rest of the world. “99.9% of the DNA from two people will be identical. The 0.1% of DNA code sequences that vary from person to person are what make us unique,” (BBC. 2013). The advancements started in the late 1900’s. Scientists were using programs to help identify DNA. Eventually a forensic board opened in 1990, setting a standard of laws and standards that the new base of technology would have to follow. DNA identifying is a cellular biology process. It takes place by using a sample of DNA, usually one from the potential criminal found at the crime scene or a victim's body, then “the DNA is isolated from the cells and millions of copies are made, using a method called 'polymerase chain reaction', or PCR. PCR uses a naturally occurring enzyme to copy a specific stretch of DNA over and over again. Having lots of DNA makes the genetic code easier to analyse. The DNA molecules are then split at particular locations to separate them into known 'chunks' and the code at those specific points is analysed to create a DNA fingerprint,” (BBC, UK 2014). DNA forensic technologies have made some very important advancements. Such as freeing David Vasquez, a wrongly convicted man of one of serial killer Timothy Wilson Spencer’s crimes. DNA testing has also made historical advancements proving that Anna Anderson who had famously claimed to be the Grand Duchess Anastasia, the only survivor of the Russian royal family. After Anderson died, DNA tests proved she was no relation to the Imperial family.Forensic testing is usually broken down into two ways. First is Y-marker analysis, used when men are involved and often sexual assault cases. As its name suggests, this technique examines several genetic markers found on the Y chromosome. Scientists look into the Y gene and

Each lab bench will make, and run one gel electrophoresis per table. Once the gel is ready to be loaded, load five microliters of PCR DNA ladder into the first well, as a standard. This should be found in a tube in and ice bucket. Next add two microliters of 6x loading dye into the six sample tubes. The dye should be mixed in thoroughly by gently pipetting up and down after adding the dye. Following that you should load fifteen microliters of each sample into the following six wells. Since lane one will have the DNA ladder lane two starts the samples using the orange tube, then the blue, yellow, red, green, and pink tubes go into lanes three, four, five, six, and seven respectively. Once all the samples are loaded turn on the electrophoresis machine, and wait until the bromophenol blue tracking dye has migrated at least half the length of the gel. Lastly using gloves carefully remove the gel and carry it to the UV light box to view, and photograph the gel (Hass C., Woodward D., and Ward A., 2010.).

There are three steps in PCR, and they are; (1) Denaturing- DNA molecules are heated and separated into two single strands. (2) Annealing- A primer is used to start the process of building a new strand of DNA. (3) Extension- dNTPs are added to the reaction mixture to build a new complementary strand to the template strand. By using a primer a new strand grows in 5’ to 3’ direction and the template is 3’ to 5’ and they can be amplified by the original template.

There are many different ways that one can extract DNA from biological evidence. Forms of biological evidence are hair cells, tissues, blood, semen, skin cells, muscles, brain cells, bone, hair, waste, and finger nails. Each involves similar but different extraction techniques. Extraction is a technique in which out of the entire sample, DNA is the only thing left to have ("DNA Extraction”). There are four different steps when it comes to extracting the DNA, preparing the sample, binding the DNA to the membrane, wash, and elution of pure DNA (Kennedy). Preparing the sample involves, taking the sample and putting into a microcentrifuge tube and adding buffers into the sample. Binding the DNA to the membrane is important because when the DNA sample is transferred over to the column there is silica (Kennedy). In the binding stage, ethanol is added which allows for the nucleic acids to stick to the silica more, allowing the DNA to bind. The next stage is the wash stage, the wash stage uses a lot of buffers

There are various problems and limitations, DNA profiling isn’t infallible; these issues can refer to the newer and older technologies.

There are many hopes for the future of DNA forensics. One hope is to better some of the techniques already used in existing systems, such as STR analyses (short tandem repeat analyses). Making a more foolproof system that provides equivocal tests for comparing more loci at one time is another hope for the future of DNA

Use of DNA polymorphism has proven particularly pertinent in criminal investigations since DNA sequencing can be used to identify suspects and hence evaluate their potential guilt. In order to be able to prove an individual was responsible for a crime, a specific DNA sequence must be amplified (lengthened) by specialised strands of DNA (known as primers) in the process of Polymerase Chain Reaction (PCR), to differentiate it from any other repeat sequence in the human genome. This process of amplifying every DNA sample used is repeated 28 times to generate millions of DNA copies so that the samples can be visibly seen in the agarose gel when placed under the UV light. Subsequently, observations can be made about how far the DNA fragments of each sample have travelled along the agarose

DNA evidence can definitively link a suspect to either a crime scene or victim. Nuclear DNA evidence has been recovered from blood, semen, saliva, skin cells and hair. Furthermore Mitochondrial DNA can be recovered from both bone and teeth dating back thousands of years. Laboratory analysis of DNA evidence generally involves the sample being amplified and quantified by a form of the Polymerase chain reaction known as Quantitative PCR or qPCR. (PCR) amplification of any sample recovered followed by sequencing via Capillary electrophoresis in order to obtain a DNA profile which can be compared to suspect DNA. DNA can also be extracted from animals and used to at least identify the species, for example bird or bat remains on an airplane or wind

PCR means Polymerase Chain Reaction, PCR is a technique used to analyze DNA. If we add the right primers for Ebola we will see Ebola DNA grow and no other DNA. What is a primer? It is a short strand of DNA or RNA (18-22 bases) it serves as a good starting point for DNA synthesis and it is essential for DNA replication. Why? The enzymes that catalyze the process can add new nucleotides to an existing strand of DNA.

Since its invention in 1983 by Kary Mullis; PCR has radically changed our approach to molecular biology. It brought forward a new perspective in the field of medical sciences and genetics. Any gene from any organism could be isolated using PCR.