Essay: DNA's effect on Forensic Science

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The aim of this investigation is to examine the structure and steps involved in a forensic investigation, to determine the reliability of DNA evidence through DNA profiling. This will be explored through the process of DNA extraction, the equipment used, and the steps of identifying genetic information of people at a crime scene; where the benefits and limitations of forensic science will be determined.

What is DNA?

Deoxyribonucleic acid, commonly referred to as DNA, is the genetic code found in every cell, of all living organisms (Genetics Home Reference, 2017). Structurally, DNA consists of 4 chemical bases: adenine (A), Guanine (G), Cytosine (C) and Thymine (T) (Genetics Home Reference, 2017). These bases pair together (A with T and C with G) to form base pairs (Genetics Home Reference, 2017). These base pairs connect to two nucleotides; each containing: a sugar (ribose) molecule, a phosphate molecule and a nitrogenous base (Genetics Home Reference, 2017). This forms a ladder shaped molecule that coils into a spiral, to form a double helix (Genetics Home Reference, 2017).

Process of DNA extraction:

The process DNA extraction is the expulsion of DNA from a cell; in order to purify the DNA molecule, to provide ease in the examination. The process of DNA extraction is found in the following steps:

Step 1: Break open cellular walls through physical force, in the form of crushing, grinding or vortexing (Science Learning Hub, 2009). Place the result of this into a Sodium chloride solution, as the positive charged sodium ions ensure protection on the negative charged phosphate found in the nucleotides in the DNA (Science Learning Hub, 2009). In addition, detergent is supplemented, in order to break down the liquids found in the cell membrane and nuclei (Science Learning Hub, 2009), causing DNA to be released due to the disarray in the membrane.

Step 2: Other materials attached to the DNA, such as proteins and cellular debris, are removed through the use of a protease (protein enzyme) (Science Learning Hub, 2009). The protease deteriorates the unwanted debris and proteins in order to create a clean sample (Science Learning Hub, 2009).

Step 3: Carefully placed into the DNA sample, Ice-cold Ethanol or Isopropanol is gently stirred (with a stirring rod), creating a precipitate that is easily obtained, by spooling it out (Science Learning Hub, 2009).

Step 4: It is now further cleansed, in a mildly concentrated alkaline buffer (Science Learning Hub, 2009).

Step 5: In order to measure quality, quantity and concentration of the DNA sample, optical density readings are taken by a spectrophotometer (Science Learning Hub, 2009); which is a vital element of Forensic science, to prove the reliability of the DNA, as a source of evidence.

Commonly ‘blood, semen, saliva, urine, faeces, hair, teeth, bone, tissue and [skin] cells’ (NFSTC, 2013) are the major and most common genetic material found at a crime scene. These genetic materials are typically found on items of: ‘masks, hats, gloves, clothing, tools, weapons sexual assault evidence kits, underclothes, bedding, dirty laundry, fingernail scrapings, cups/bottles, cigarettes, toothpicks, toothbrush, facial tissue, hairbrush, eyeglasses, condoms, tape, ligatures (rope, wire, cords),’ (NFSTC, 2013).

How Genetic material is collected:

The genetic material is collected through the following steps:

‘ Wet Blood ‘ Using a Gauze pad, forensics will submerge it into wet blood, where it will immediately be frozen or refrigerated. It then immediately is sent to the laboratory. After 48 hours of idle, the genetic material will become inoperable.

‘ Dry blood ‘ If this genetic material is found on an item of clothing, the clothing is wrapped in clean paper, and labelled. Where it then is immediately sent for examination in the laboratory.

‘ If dry blood is found on a large item, that cannot be moved. The dry blood will be scrapped into a plastic bag, labelled and sent for examination in the Lab. However, if the item can be moved, the stained area is to be covered with paper, and sealed down with tape. This prevents contamination. This will be labelled and shipped to the laboratory.

‘ If it is a small item, contaminated with dry blood, the item will be labelled and immediately sent to laboratory.

‘ Saliva ‘ Saliva is collected with a sterile gauze pad or swab, and preserved in a paper bag.

‘ Semen ‘ If this is found whilst still moist, it will be air-dried, wrapped in paper and also packaged and preserved in paper.

‘ Hair ‘ Hair is collected with tweezers and placed in a small coin envelope. After doing so it is placed in a larger envelope, packaged and sent to the laboratory. However, if pubic hair is retrieved it is combed previously to being packaged.

Once DNA material has been collected it goes through the processes of:

‘ Extraction ‘ This is the expulsion of DNA from a cell (NFSTC, 2013)

‘ Quantitation ‘ To establish the quantity of DNA (NFSTC, 2013)

‘ Amplification ‘ The replication of DNA, to determine the DNA’s characteristics (NFSTC, 2013)

‘ Separation ‘ The process of separating the replicated DNA, for documentation for future identification. (NFSTC, 2013)

‘ Analysis & Interpretation ‘ The comparison of DNA to known DNA profiles(NFSTC, 2013)

‘ Quality Assurance ‘ Reviewing analytic reports for accuracy. (NFSTC, 2013)

Known DNA profiles, are samples of DNA that have previously been analysed. This stays in the system for future reference, or to compare DNA found in a new investigation. The general reason for DNA to be in the system is due to: Convicted offenders, previous arrestees, unidentified people and missing persons (volunteered by family members) (NFSTC, 2013).


In 1987, forensic evidence’s first dealings in the UK ultimately were successful (Forensic Outreach, N.D.). 15 year old girl, Lynda Mann was reported to be abducted in Narbourough, England (Forensic Outreach, N.D.). She was found the next day, raped, and murdered (Forensic Outreach, N.D.). 3 years later, another girl was abducted, raped and murdered with similar circumstances to Lynda Mann’s (Forensic Outreach, N.D.). Richard Buckland, local resident confessed to police that he had committed the second crime, however, not the first (Forensic Outreach, N.D.). During this time, a new technique emerged, called ‘Genetic fingerprinting’; this compares genetic material found on the victim or at the crime scene, to the suspect (Forensic Outreach, N.D.). This technique ultimately proved Richard’s innocence in both cases, claiming to have confessed due to pressure by police (Forensic Outreach, N.D.).

5,500 local male residents were tested, using this new forensic procedure (Forensic Outreach, N.D.). 1 of the men, Colin Pitchfork, persuaded one of his friends into completing his test; however, Colin began bragging that he had fooled the system (Forensic Outreach, N.D.). Listeners anonymously reported this (Forensic Outreach, N.D.). He was forced to complete the test, where his semen matched the genetic material found in both victims (Forensic Outreach, N.D.).

In this case, without the usage of forensic science, innocent man Richard Buckland would have been incarcerated for a crime he did not commit, where murderer and rapist Colin Pitchfork, would be free, and residents of the area’s safety would have been eliminated.

Forensic science has the ability to prove if a suspect or witness is lying in court. In the circumstances of a car accident, where it is claimed the victim had not consumed any alcoholic beverages. A forensic scientist is able to test the alcohol concentration in that person.


‘ Determination of age ‘ For example there is no evidence to determine whether a fingerprint is recent or old. (UKessays, 2015)

‘ Cross Contamination (UKessays, 2015)

‘ DNA mix-ups (UKessays, 2015)

‘ Disho
nest DNA analysts (UKessays, 2015)

‘ General Mistakes can cause innocent suspects to go be incarcerated. Or guilty suspects to be proven innocent. (UKessays, 2015)

‘ Faulty Equipment (UKessays, 2015)

Forensic science has am extremely high reliability. If an error has occurred, an innocent man could be incarcerated due to this.

In conclusion, Deoxyribonucleic acid is the Genetic material found in every cell of every living organism. It is used in forensic investigations, through DNA profiling. To extract DNA from a cell, in order to analyse the genetic material, through physical force in the form of crushing or vortexing, the cellular walls are broken. The result of this is placed in a salt solution. Detergent is supplemented, which causes the DNA to be released due to the disarray. Excess cellular debris and proteins are removed through a protease. Ice-cold Ethanol or Isopropanol is supplemented into the DNA sample, and gently stirred. This creates a precipitate that causes DNA to be easily obtained. It is further cleansed in a mildly concentrated alkaline buffer. DNA is commonly found on items of: ‘masks, hats, gloves, clothing, tools, weapons sexual assault evidence kits, underclothes, bedding, dirty laundry, fingernail scrapings, cups/bottles, cigarettes, toothpicks, toothbrush, facial tissue, hairbrush, eyeglasses, condoms, tape, ligatures (rope, wire, cords),’ (NFSTC, 2013). The most common genetic material found at a crime scene is: ‘blood, semen, saliva, urine, faeces, hair, teeth, bone, tissue and [skin] cells’ (NFSTC, 2013). Forensic science creates a reliable source of evidence and is able to identify unknown criminals in crime scene, through their genetic information. This creates a higher reliability as a witness could be lying, however genetic material cannot be manipulated.

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