Last Updated 16 Jun 2020

DNA Fingerprinting

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DNA contains genetic material and information that makes up each individual trait. Every person can be identified by providing his or her genetic information based on a particular DNA strand. DNA information is an effective way of identifying persons if it is used properly. It is used to identify humans in different situations such as crime scenes, accident scenes, paternity testing, soldier remain identification, inheritance claims, missing person investigations, and convicted felon databases. Although there are different ways to identify DNA, the most common method is DNA fingerprinting. The process that was used in the lab experiment was gel electrophoresis.

Before DNA fingerprinting, a different method called Blood typing was used. This method was used to identify people by taking a sample of dried blood. But this method had some disadvantages; for example, many people who receive blood by transfusionundergo changes in their blood characteristics,making difficult the blood typing; also, blood typing required an amount of body fluid that sometimes was not enough or that other times was deteriorated, making it impossible to do the blood typing. So, because of these disadvantages, DNA fingerprinting began to be used as a forensic tool.

Restriction Fragment Length Polymorphisms (RFPL’s) is a restriction enzyme that recognizes a specific strand of the nucleotides in DNA. This strand is different in every individual; the restriction enzymes cut the part of the DNA strand that is different, and it is used in gel electrophoresis to identify a person. For example, in crime scene investigations the DNA sample that is found is compared with the sample of suspects bythe gel electrophoresis procedure in order todetermine if the suspect committed a crime.

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When doing the gel electrophoresis process,different DNA strands are set in the lanes of the gel, and they are run by an electrochemical gradient from negative to positive to separate these strands. When the strands separate, they group themselves in bands. The shortest bands travel at higher speed; therefore, they are found at the end of the gel. This experiment gives the possibility to identify which bands are the same to the one that was found in the scene, allowingreaching the objective, which is to uncover who is responsible at the crime scene.

MATERIALS

Restriction enzyme
Colored micro-tubes contain DNA samples
DNA loading dye
Agarose gel
Pipet
Tips
Electrophoresis apparatus
TAE Buffer
Centrifuge
120 ml of 100X blue stain.
Tray
40 to 50 Celsius of tap water.
Ice

METHODS

1. In the lab experiment DNA samples were provided in colored micro-tubes that were incubated in ice.

2. 5 ulof DNA loading dye were placed in each sample tube and each tube was flipped gently with afinger. 3. A centrifuge was used to mix the DNA sample with the loading dye. 4. Theagarose gel was placed with thetop of the gel to the negative side in electrophoresis apparatus, and the electrophoresis box was filled with TAE buffer until it had completely covered the gel. 5. A pipet was used with different tips, and DNA samples were loaded into different lanes of the gel in the following order: Lane 2: DNA sizes marker 10ul

Lane 3: Suspect one, 20 ul
Lane 4: Suspect two, 20 ul
Lane 5: Suspect three, 20 ul
Lane 6: Suspect four, 20 ul
Lane 7: Suspect five, 20 ul

6. The lid was placed in the electrophoresis chamber and plugged into the power supply. The power supply was turned on and the samples were electrophoresed at 100V for 30 minutes. 7. After that, the gel was removed carefully from the gel box and placed in a tray. 8. 120 ml of 100X fast blast of DNA stain was added. The gel was stained for two minutes with gentle movement. 9. The gel was transferred into a large tray and the gel was rinsed with warm tap water twice, with gentle shaking.The gel was leftto dry for 24 hours.

Loadind dye was Centrifuge wasused Gel was placed DNA samples were placed in each to mix DNA and electrophoresis loaded in the gel micro-tube samplesloading dyeapparatus

Electrophoresis Gel was placed in aGel was transferred Gel was rinse until chamberwas connected tray filled with to a clean tray the excess of stain to the power supply stain with warn tap water was removed

RESULTS

Gel Electrophoresis

Molecular marker
Crime Scene
Suspect 1
Suspect 2
Suspect 3
Suspect 4
Suspect 5
Band
Distance
(mm)
Actual size (bp)
Distance
(mm)
Approx
Size (bp)
Distance
(mm)
Approx.
Size (bp
Distance
(mm)
Approx.
Size (bp)
Distance
(mm)
Approx.
Size (bp)
Distance
(mm)
Approx
Size (bp)
Distance
(mm)
Approx
Size (bp
1
4
23,000
10
5,700
12
5,000
12
5,000
10
5,700
12
5,000
12
5,000
2
7
9,400
12
5,000
17
2,500
15
4,400
12
5,000
18
2,300
14
4,600
3
9
6,500
19
2,250
18
2,300
17
2,500
19
2,250
22
2,200
19
2,250
4
15
4,400

5
18
2,300

6
22
2,000

DNA Bands Data Table

Based on the results of the gel electrophoresis, suspect number three’s DNA sample matches with the crime scene sample, not only because they look the same, but also because of the distance that strands travel along the gel, and the base pairs that they contain. The DNA bands of the crime scene sample were found at 10, 12, and 19 mm, instead of the bands of suspect numbers one, two, four, and five,which were found at different distances than the crime scene sample. Only the bands that correspond to suspect number three were found with similar distances to the crime scene one. Finally, the base pairs of the DNA bands of suspect number three and of the one found in the crime scene were 5,700 bp for the first set of DNA bands, 5,000bp for the second set, and 2,250 bpfor the third set. All of these results indicate that suspect number three was responsible for the crime committed in the crime scene.

DISCUSSION AND CONCLUSIONS

In conclusion, DNA fingerprinting and electrophoresis were used to determine the size of the unique strand cut by restriction enzymes that identifies the individual who was responsible in the crime scene. This lab taught how to conduct an electrophoresis experiment, and how importantthe use of this method is to solve a problem that is common in society. In this process different DNA samples were provided, and after doing the electrophoresis experiment, it was found that the suspect committed the crime. DNA profiling, whichwascalled at first DNA fingerprinting, is used for other purposes, as was mentioned earlier. One of those is paternity testing.

At this time, this method has become less difficult than what people may believe. Some laboratories provide this service, sending to their clients a kitwith everything that is needed to collect a sample of DNA.This sample, which could be a small portion of cheek tissue taken with a swab and put in a labeled envelope, is returned to the lab to be analyzed. Sometimes when this type of test is required for legal reasons, the sample to be evaluatedis taken under supervisionin order to avoid any intentional errors. DNA fingerprinting and profiling have become common processes, but also these have become very important because they help to get accurate results by using genetic information in order to solve different situations such as a crime or paternity identification.

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DNA Fingerprinting. (2016, Aug 08). Retrieved from https://phdessay.com/dna-fingerprinting/

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