DNA Fingerprinting: Steps and Applications

DNA fingerprinting is a molecular biology technique used to identify the individual by sample of their respective DNA profiles. DNA fingerprinting was invented in 1984 by British geneticist Sir Alec Jeffreys. Each individual has a unique pattern of minisatellite and microsatellite DNA, except identical twins or monozygotic twins.

• In DNA fingerprinting also known as DNA profiling, unique nucleotide sequences of a particular DNA are utilised to determine the identity of a person. 
• The applications of DNA fingerprints are widely seen in criminal investigations, paternity tests, and other forensic purposes. 

What is DNA Fingerprinting? 

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DNA fingerprinting is a modern approach of identifying an individual with his or her DNA samples. These human DNA samples are obtained from the target individual’s hair, saliva, blood, and skin cells. This technique is getting more attention nowadays due to the higher crime rates.  

Principle of DNA Fingerprinting

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The principle of DNA fingerprinting is based on a genetic theory that explains that DNA is the basis of genetic and evolution. The DNA sequences varies in each and every individual (except identical twins) which is main cause of variation and genetic diversity. These long sequences of DNA are identified by DNA fingerprinting technique. 

• The basic requirements of DNA fingerprinting method are variable number of tandem repeats and short nucleotide repeats also called minisatellites and microsatellites. 
• These are numerous small non-coding but inheritable sequences of bases which are repeated many times.

DNA Fingerprinting Steps

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The DNA fingerprinting is a multistep process utilised mainly for Biomedical research and Forensic purposes. All the steps involved in the process are discussed below in detail: 

Isolation of DNA

The first step of DNA fingerprinting is the extraction of DNA from desired cells by chemical treatment. Common sample types used today include blood and cheek swabs. These samples must be treated with a series of chemicals to break open cell membranes, expose the DNA sample, and remove unwanted components – such as lipids and proteins to get a pure DNA. 

PCR Amplification

The amplification of DNA is done usually to get enough amount of sample for further research and analysis. This is done through another molecular biology technique called polymerase chain reaction (PCR). Denaturation, annealing, and primer extension are three important steps of PCR. Through this, extra copies of collected DNA are amplified. 

Treatment with Restriction Endonucleases

The amplified DNA sequences are now treated with restriction endonuclease enzyme which acts as a molecular scissor. This enzyme cuts the DNA at a particular site in order to isolate variable number of tandem repeats (VNTRs). Restriction enducleases are DNA enzymes that attach to specific DNA sequences and create breaks in the DNA strands.

Separation of DNA Fragments by Gel Electrophoresis

Southern Blotting

Now that the DNA fragments have been separated based on their size, they must be transferred to a medium where scientists can “read” and record the results of the electrophoresis. To do this, scientists treat the gel with a weak acid, which breaks up the DNA fragments into individual nucleic acids that will more easily rub off onto paper. They then “blot” the DNA fragments onto nitrocellulose paper, which fixes them in place.

Treatment with Radioactive Probe

Now that the DNA is fixed onto the blotting paper, it is treated with a special probe chemical that sticks to the desired DNA fragments. This chemical is radioactive, which means that it will create a visible record when exposed to X-ray paper.

• This method of blotting DNA fragments onto nitrocellulose paper and then treating it with a radioactive probe was discovered by a scientist named Ed Southern – hence the name “Southern blot.”
• Amusingly, the fact that the Southern blot is named after a scientist and not the direction “south” did not stop scientists from naming similar methods “northern” and “western” blots in honor of the Southern blot.

X-Ray Film Exposure

The last step of the process is to turn the information from the DNA fragments into a visible record. This is done by exposing the blotting paper, with its radioactive DNA bands, to X-ray film. X-ray film is “developed” by radiation, just like camera film is developed by visible light, resulting in a visual record of the pattern produced by the person’s DNA “fingerprint.”

• To ensure a clear imprint, scientists often leave the X-ray film exposed to the weakly radioactive Southern blot paper for a day or more.
• Once the image has been developed and fixed to prevent further light exposure from changing the image, this “fingerprint” can be used to determine if two DNA samples are the same or similar.

Applicatons of DNA Fingerprinting

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This process is frequently used in following cases:

• Criminal investigations to determine whether blood or tissue samples found at crime scenes could belong to a given suspect.
• Paternity tests, where comparison of DNA markers can show whether the parents are biological.
• Match tissues of organ donors with those of people who need transplants.
• Identify diseases that are passed down through your family.
• Help find cures for those diseases, called hereditary conditions.

In science, DNA fingerprinting is used in the story of plant and animal populations to determine how closely related species and populations are to other species and populations. Further, it can track their spread over time. This ability to look directly at an organism’s gene markers has revolutionized our understanding of zoology, botany, agriculture, and even human history.