Essay What is the Polymerase Chain Reaction (PCR)

Contamination can occur when transferring DNA or the collection of DNA evidence. In the case involving Mr. Farah, he was wrongful charged of rape although he had appealed in the High Court with the basis of the scientists not having said he was undisputedly the perpetrator. The scientists said that it was a very small chance that it was not Mr. Farah which he argued was still a reasonable doubt. The judges dismissed the case within twenty minutes but it was later found that the evidence was contaminated. Other examples include R v. Rendell (1999) and R v. Carroll (2002.)Though technology is advancing, the process of collecting, processing and analyzing DNA has faults. There needs to be more training, procedures and checks put in place for the system to be effective. Faults in evidence presents to be ineffective justice as although the jury weighed up the evidence, there was inadequate access to allow him to refute the claims and lead to wrongful convictions.

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.

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.).

What does the PCR do? PCR is a method by which fragments of DNA can be duplicated. This makes PCR more sufficient amongst other Felds in forensic science.

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.

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)

From 1990-2003 the Department of Energy coordinated a project called the Human Genome Project, in which it asked, "Why screen for individuals at increased risk for genetic diseases who do not exhibit symptoms? On the pro or benefit side, we want to reduce morbidity and mortality. The idea is, if we could find the disease early before

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.

The mixture was  heated to denature the template DNA, then cooled so that the primer can bind to the single-stranded template. Once the primer has been bound, the temperature was raised again, allowing DNA polymerase to synthesize new DNA starting from the primer. The DNA polymerase will continue adding nucleotides to the chain until it add a dideoxy nucleotide instead of a normal one. At that point, no further nucleotides can be added, so that the strand will end with the dideoxy nucleotide. The process was repeated in a number of cycles. At the end of cycle, the dideoxy nucleotide will be incorporated at every single position of the target DNA in at least one reaction. That is, the tube will contain fragments of different lengths, ending at each of the nucleotide positions in the original DNA. The ends of the fragments will be labeled with dyes that will be indicating  their final nucleotide. The fragments won’t be labelled and a matter of chance whether a dideoxy nucleotide gets incorporated in a particular polymerization reaction. Some of the newly synthesized pieces of DNA will consist only of normal, unlabeled nucleotides, and will simply end when the

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.

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

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

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

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

Polymerase chain reaction (PCR) can be termed as an enzymatic, molecular “xeroxing” process in which a particular region of DNA is replicated several times to yield thousands of copies of a specific sequence. The process of PCR employs a precise pattern of heating and cooling of samples in a thermal cycler, over 30 cycles.