DNA Fingerprinting Essay

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Every living cell in humans, as well as other living organisms, have DNA (deoxyribonucleic acid) which is a genetic material coded by the proteins in the cells. In every individual's DNA, there are unique components known as polymorphins, and this is the elements which help in differentiation between proteins of one person with another. Thus, laboratory scientists, as well as forensics, can be able to conduct an assessment of this genetic materials and be able to tell the DNA fingerprint of a person (Edvotek, 2007) Therefore, the information extracted can be used in the determination of several cases such as the paternal or maternal origin of a person, diagnosis of various genetic health conditions that might be inherited from generation to generation as well as identification of human remains. Therefore, even with little samples collected from a crime scene, the DNA of the perpetrator if left behind can be determined, and tests conducted on the suspects to verify the actual individuals involved in the crime (Li, et la., 2012). For this assignment, I am going to provide detailed information concerning the manner in which DNA can be used to identify a crime suspect. Therefore, the procedures involved as well as significant tests conducted will be discussed.

Research question: How is DNA analysis used to identify a crime suspect?

Methodology and materials

Step 1: DNA Extraction

The fast method used in attempts of identifying a suspect is DNA extraction. Therefore, to get access to the DNA, the cells found in the scene have to be opened and hence a detergent is utilized for this purpose. The mechanism of action of the detergent is breaking the cell membrane of the cell as well as other membranes present such as the nuclear membrane because the DNA is always stored in the cell nucleus. Thus, the phospholipids components of the membranes are interfered with by the detergent leading to the disruption of the tertiary and quaternary structure of the proteins. Use of sodium chloride establishes a salt bridge between the DNA molecules. Deactivating chemicals are always used to render inactive the nucleases produced in the breaking down the process of the nucleus. After the above procedure, ethanol is utilized to extract DNA from the solution through precipitation process by drawing the water away.

The procedure, DNA extraction was simulated from the check cells after the mouth was rinsed clean to eliminate fine debris from the mouth.  A ¼ OZ of sterile water was poured into the cup and swished around the check by use of the tongue to loosen check cells into the water. This took approximately one minute. The water was then deposition back in the cup, and a ¼ OZ of detergent and sodium chloride was added and mixed well. Ethanol solution was added to the fluid in the cup in the ratio of 1:1. Precipitation of the DNA automatically should take place making the fluid to have a mucus-like color.

Step 2: Polymerase Chain Reaction (PCR)

After extraction of the DNA from the cells, numerous copies of the short tandem repeats regions of the DNA are made through PRC. Making a lot of copies of the DNA is necessary because in most cases very little DNA is available for analysis. For this experiment, preferred DNA samples were sent to the laboratory the PRC process to be done.

Step 3: Separation of DNA Fragments by Agarose Gel Electrophoresis

The gel electrophoresis allows the forensics and laboratory scientists to segregate and visualize DNA based on size (fragment length). Normally, DNA has negative charge because of the phosphate groups in the sugar-phosphate backbone. When the DNA is introduced in an electrical field between the negative and positive electrode, the molecules migrate through the positive electrode. The fluid agarose is usually isolated from seaweed and once the DNA is introduced in its gel it the molecules migrates via the porous network of the gel. The speed in which it migrates depends on the size of the fragment. Usually, small fragments move faster compared to large-sized fragments because of the high surface area to volume ratio, and hence the large ones end up in the bottom of the gel. After some time, DNA can be visualized and once can tell the differences in the size of the DNA by comparing how far the DNA traveled.

Several methods can be utilized to visualize the DNA such as molecular weight standards, but for this experiment ethidium bromide (EtBr), a chemical that binds readily to fluoresce and DNA when exposed to ultraviolet light was utilized. The above property makes the ethidium bromide a suitable molecule to use when visualizing DNA.


A gel custing tray was well set up electrophoresis, and the well-forming comb was inserted. 0.8% agarose solution (about 35 mL) was poured slowly into the casting tray. The bubbles that form to the side of the tray were Push away by use of pipette tip. The gel was allowed to set completely. Approximately 20 minutes should be given for it to settle. The gel was placed in the electrophoresis chamber with the wells oriented towards the negative (black) electrode, and enough Electrophoresis Buffer (1X TAE) to cover the gel was added. The comb was removed from the gel and the wells exposed. The sample was micro pipetted into the wells through the buffer in a systematic order. Separate tips were used for different samples. The lid was placed on the gel apparatus, and the leads were connected to the power supply. The power was turned on, and the gel runs at 125 V until the tracking dye was close to the bottom of the gel. The bubbles coming off was a clear indication of current flow. The gel was stained with ethidium bromide to visualize the bands. The standard procedure was utilized in the staining as well as visualization o the gel via a transillumination UV source and photograph.


The process of DNA extraction leads to the production of while precipitates (the DNA) from the cells of the cheeks. The solution appeared like mucus while in the cup due to the while color of the precipitate. In such a state the DNA could be spooled from the suspension. The texture of the DNA is very soft on touch.

Precipitated solution with DNA

The gel profile was well labeled and captured to indicate the lab handouts. The following is a picture of the gel profile.

Profiles gel obtained from the experiment

There were seven bands of the DNA extracted from the scene of the crime which indicated that seven different DNAs were present in the chromosome of the suspect. The sequencing or the order of the band is shown in the profile above. The part of the DNA used in

The gel on a transillumination UV source


The DNA extracted was pure because the aseptic technique was used and necessary precautions taken to ensure that the DNA was not contaminated or affected during the procedure. Also, a chemical was used to deactivate nuclei produce as the DNA was being separated from the major cell nucleus. The detergent used was perfect in interfering with the cell membranes as well as nucleus membrane because it successfully interfered with the protein components in the membranes and hence rendering it inactive. The DNA contains molecules of polynucleotides which are made up of long chains of nucleotides. The nucleotides are made up of elements such as guanine, cytosine, thiamine, and adenine, which from the sequences in both DNAs and RNAs. The nucleotides code for certain genes which leads to expression of certain traits in the body of a person. Other macromolecules could have been detected by use of confirmatory tests for lipids, carbohydrates, and proteins other than the ones composed in the DNA (Li, et la., 2012).

The procedure required a lot of caution because very few DNA samples were available and hence much care was to be provided to avoid any destruction. Also, accessing the right chemical that would prevent nuclei from forming was a challenge. The issue was to determine the best DNA sample to select for the PCR. For the sake of acquiring a better sample from the solution, the appropriate chemical for deactivation nucleus could have been used as well as the use of cells that are cleaner such that they are less contaminated (Mapes, et al., 2016)

The gel profile obtained from the experiment was different from the ideal one because the standard conditions and control measures were not keenly applied. The other issue is that in the experiment we used ethidium bromide which is good for use in visualization but it intercalates into DNA and acts as a DNA mutagen. Thus, it can facilitate mutation of the DNA leading to the acquisition of different results from the expected. I could have utilized the molecular weight standard to obtain a similar result that resembles the ideal gel profile.

Separation of DNA fragments by gel electrophoresis is a procedure utilized because DNAs have a negative charge and since electrophoreses have both positive and negative charges, it serves as the best option for separation. The concept of opposite charges attracts applies here because the phospholipid in the DNA is attracted to the positive electrode (Dayla, 2004). Other molecules migrate to the negative rods because they have positive net charge. Hence, to balance the charges, they have to bind and to the electrode instead of staying as free electrodes. The large fragments are usually found suspended in the solution used for electrophoresis. The small fragments because they travel faster they are found at the bottom of the gel. On the other hand, the gel electrophoresis had a close association with the hypothesis because it can help in identification of a suspect in a crime scene.


The DNA was successfully extracted and run through tests to help in the determination of the individuals it belonged. The process of electrophoresis was very successful in the separation of DNA from other molecules present and hence making it easier for visualization. The results obtained were not very clear when compared to the ideal procedure, and hence it would require better material such solutions used for visualization availed. If a proper test is done on DNA, a lot of information concerning the owner can be extracted including health status and information regarding genetic line up when compared to the DNAs of the relatives.


Edvotek, 2007. The Biotechnology Education Company. “PCR Amplification of DNA for Fingerprinting.” http://www.edvotek.com/130.

Dayla R. 2004. How does DNA Fingerprinting work? Article from the Naked Scientist website. http://www.thenakedscientists.com/HTML/articles/article/dalyacolumn8.htm/

Li, Z., Yang, X., Dong, S., & Li, X. (2012). DNA breakage induced by piceatannol and copper (II): Mechanism and anticancer properties. Oncology letters, 3(5), 1087-1094.

Mapes, A. A., Kloosterman, A. D., de Poot, C. J., & van Marion, V. (2016). Objective data on DNA success rates can aid the selection process of crime samples for analysis by rapid mobile DNA technologies. Forensic science international, 264, 28-33.

August 04, 2023

Crime Science

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