A Step-by-step Explanation of the DNA Fingerprinting Process (2024)

A Step-by-step Explanation of the DNA Fingerprinting Process (1)

DNA fingerprinting has revolutionized criminal investigations to pin down real culprits. As interesting as it sounds, it has a sophisticated step by step procedure. This article will give you complete information on its process.

Every person is born with a unique identity. Earlier it was thought that this unique character was only abstract qualities like nature or behavior that distinguished one person from the other. But the DNA fingerprinting process has proven that there exists material evidence which can distinguish between any two individuals in this world. The science of DNA sequencing has developed a lot since the first profiling was done by Sir Alec Jeffreys in 1985, in England. There were many research activities undertaken earlier to understand the process of DNA fingerprinting. Since his discovery at the University of Leicester, human genetic science has made great strides in the identification of unique DNA patterns.

Principle

The entire genetic information of an individual is called genome. Genome contains the DNA sequence, which has both coding and non coding genes. The DNA sequences of humans are 99% similar in every individual. However, the other 1% is what makes each one of us unique. This 1% sequence mainly has specific codes that repeat itself throughout the sequence. These are short and varied sequences, and are known as VNTRs (Variable Number of Tandem Repeats). The frequency and position of these repeats vary greatly from one individual to the other. DNA fingerprinting uses such VNTRs from an unknown DNA sample to compare and match with the known.

Technique

The process is summarized below with a flowchart for better understanding:

A Step-by-step Explanation of the DNA Fingerprinting Process (2)

The various steps involved are explained below:

Step 1: To begin with, one should have a source of DNA sample. This source could be a single strand of hair, sem*n, blood (a single drop will work too!), saliva, cheek cell, etc. During criminal investigations the hair, sem*n, or blood of the suspect is collected for further analysis.

Step 2: The next step is to extract the DNA sample from its source. The extraction process is devised in a way to break down the cell membrane and release the DNA to its outer environment. Detergents are used for this purpose. They tend to break open the cell membrane by forming micelles with protein and lipid entities of the membrane.

Step 3: Once the DNA is extracted, it is subjected to digestion by restriction endonucleases. These are enzymes that cut a DNA fragment at specific sites which it recognizes. It means that each restriction enzyme (R.E.) recognizes a specific DNA sequence and cuts at a specific site. For example, let us consider a R.E, “R” which recognizes a specific sequence ACTTT which it cleaves between C and T. In the given example, let us consider a double stranded DNA sequence.

GGCAACTTT….
CCGTTGAAA….

R will cut the sequence at the following site:

GGCAAC / TTT
CCGTTG / AAA

Remember that the cleaving is a double strand cut, producing DNA fragments of varied lengths. These fragments are also called RFLP (Restricted Fragment Length Polymorphism). Many of these fragments will contain the VNTRs.

Step 4: These fragments are then separated by difference in their length using gel electrophoresis technique. This technique employs electric current to move the DNA fragments over a gel-based matrix. The DNA molecule is negatively charged (due to a phosphate group) and hence will move towards the positive anode in the set up. The gel-based matrix is usually made of agarose which provides tiny pores in them through which the DNA molecules can travel. The DNA samples are loaded at one end of the gel and moves to the other when electric current is applied. The larger fragments travel slowly through the gel. However, the smaller fragments travel quickly and reach further away from the sample loading point. Note that the fragments with the same length will travel with the same speed and hence the same distance. At the end of the experiment, you will obtain DNA pieces which are sorted according to their length.

Step 5: The gel containing DNA fragments are then immersed in an alkaline environment e.g. NaOH. This step helps in denaturing DNA strands into single stranded DNA. This is important to facilitate the following steps.

Step 6: The next step is the Southern blotting technique. This technique involves:

Blotting the DNA gel on to a suitable membrane. The most commonly used is the nitrocellulose membrane. However, nylon membranes are also used which have better binding capacity. The membrane placed over the gel is subjected to gentle pressure. This is done by placing a stack of paper towels, ensuring uniform pressure on the gel. The moisture from the gel is absorbed by these towels. Due to this, single stranded DNA fragments are pulled and transferred on the membrane. The membrane is now a replica of the original DNA pattern on the gel.

• The membrane is now pre-hybridized. This is done to make sure that DNA probes do not attach to the membrane surfaces but to the single stranded DNA. Commonly, salmon sperm DNA are used for the process. This blocks the probe from binding to the surface of the membrane.

• This step is followed by hybridization with a suitable DNA probe. This DNA probe is a single stranded DNA having a sequence complementary to the desired sequence (the DNA to be investigated, like DNA found at the crime site, etc).

• Before these probes are used, they are tagged with a radioactive substance or a color-inducing (chromogenic) or fluorescent dye. This helps in detecting the matched DNA visually.

• Excess probes are washed away, and the resulting membrane is visualized using autoradiography. The X-ray film thus developed shows the hybridization pattern. The DNA sample thus hybridized with the probe can be seen and studied. This hybridization pattern is called DNA fingerprint, having a sequence complementary to the probe.

Modifications of the Method

Several new techniques and procedures have made DNA fingerprinting efficient and reliable. New advancements in technology have made it possible to extract DNA from minute sources and produce results with high accuracy. Some of these are listed below:

Polymerase Chain Reaction (PCR): It is a technique that helps in synthesizing million copies of specific region/fragment of a DNA sequence. This technique is useful when a low amount of DNA is available for study or investigation. It involves denaturing the DNA strand and then annealing it at specific temperatures. DNA polymerases are used to add dNTPs (deoxyribonucleotides) at the 3′ end of the DNA to synthesize a new complementary sequence. Modification of PCR technique like RAPD-PCR, AFLP-PCR help in better and accurate results with minimum errors.

STRs (Short Tandem Repeats) and SSRs (Simple Sequence Repeats) are 2-6 base pair long repeating sequences. These are unique for every individual and are shorter than VNTRs. Hence they produce accurate DNA fingerprints.

The above processes are repeated several times, until a detailed classification is obtained, and hence distinguishing between various elements and their study is possible. The intermediate stages can vary in methods or chemicals used, but the principle remains mostly the same resulting in the completion of the process. In order to understand the process in detail, a certified laboratory can be approached, where DNA testing is carried out.

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A Step-by-step Explanation of the DNA Fingerprinting Process (2024)

FAQs

A Step-by-step Explanation of the DNA Fingerprinting Process? ›

DNA fingerprinting has four main steps: Step 1: DNA extraction from other cellular components. Step 2: Polymerase chain reaction to amplify the extracted DNA. Step 3: Restriction enzyme treatment to cut the DNA at specific sequences, resulting in fragments that are unique in size to each person.

What are the steps in the process of DNA fingerprinting? ›

The DNA testing process is comprised of four main steps, including extraction, quantitation, amplification, and capillary electrophoresis.

What are the 5 steps of DNA profiling in order? ›

For information on other DNA fingerprinting techniques, please refer to the 'Types of forensic DNA analysis' section later in this article.
  • Step 1: sample collection. ...
  • Step 2: DNA extraction. ...
  • Step 3: DNA amplification. ...
  • Step 4: DNA analysis. ...
  • Step 5: data comparison and interpretation.
Sep 22, 2023

What is the process of how a DNA fingerprint is obtained in the lab? ›

Lab workers take those strips of DNA and mix them into a gel. Then they run an electric current through the gel, which separates smaller strands of DNA from the larger ones. A dye added to the gel makes the DNA strips stand out when they're placed against an ultraviolet light or lit up with a laser.

What is the first step to making a DNA fingerprint quizlet? ›

1st step in DNA fingerprinting, DNA being taken from various body parts. 2nd step in DNA fingerprinting, Getting DNA apart from other parts of cells. 3rd step in DNA fingerprinting, Using chemicals called restriction enzymes to cut the DNA into fragments or pieces.

What is the correct order of DNA fingerprinting? ›

Correct steps or sequence of DNA fingerprinting are: Digestion of DNA by restriction endonuclesase → Separation or electrophoresis of DNA fragments → Blotting of DNA fragments to nitrocellulose membrane → Hybridisation with DNA probes → Detection of hybridised DNA fragments by autoradiography.

What are the steps of fingerprint? ›

The technician simultaneously presses the individual's four fingers (of the right hand), keeping the fingers together on the surface of the card or live scan device (at a 45-degree angle) to capture all four fingers in the allotted space. Repeat this process for the left hand and then print both thumbs.

What is DNA fingerprinting simple definition? ›

DNA fingerprinting is a laboratory technique used to determine the probable identity of a person based on the nucleotide sequences of certain regions of human DNA that are unique to individuals.

What is the basic explanation of DNA profiling? ›

DNA fingerprinting or profiling comprises any DNA-based techniques that identifies the DNA from a certain individual or group of individuals within a community of organisms. The DNA fingerprints may be used as a tool for determining the identity of a specific DNA sample, or to assess the relatedness between samples.

How is DNA fingerprinting completed? ›

DNA fingerprints are created by first isolating DNA from an unknown sample to be identified and compared with known samples. If the samples match, it enables identification. The isolated DNA (i.e. DNA that has been removed from cells and other cell components) is mixed with a restriction enzyme to create a fingerprint.

What is the process of DNA test? ›

The preferred specimen collection technique for DNA testing is by buccal (cheek or mouth cavity) swab. When buccal swabs are taken, cells are collected from the inside cheek or mouth using a long cotton swab.

How does DNA touch fingerprinting work? ›

In this, a swab is rubbed along the inside of the buccal cavity (cheek), causing scraping of epithelial cells of the suspect, and these cells are then use for DNA fingerprinting and cross matching the results with the evidence (Findlay et al., 1997).

What are the 5 steps of DNA fingerprinting? ›

Steps of DNA fingerprinting technique: Isolation of DNA → Digestion of DNA by restriction endonucleases → Separation of DNA fragments by electrophoresis → Transferring the separated DNA fragments to nitrocellulose membrane → Hybridization using labelled VNTR probe → Detection of hybridized DNA fragments by auto ...

What are the four steps in DNA fingerprinting explain? ›

DNA Fingerprinting Steps

DNA extraction. Restriction absorption or PCR intensification. Agarose gel electrophoresis, slim electrophoresis or DNA sequencing. Interpreting outcomes.

What is the basic of DNA fingerprinting? ›

The basis of DNA fingerprinting is VNTR. VNTR is a satellite DNA as a probe showing a high degree of polymorphism. This implies that there are repetitive sequences of DNA that are found across individuals of all species. Scientists identify variations in these sequences.

What are the 6 basic steps of DNA processing? ›

Q-Chat
  • Sample prep. To extract the bacterial DNA, dissolve the cell, and get rid of cellular protein.
  • PCR amplification. Make many copies of DNA.
  • PCR purification. Take out primers, extra nucleotides and other small compounds after PCR is complete.
  • Analyzing the sequence with a database of known DNA sequences.

What is DNA fingerprinting and what are its applications? ›

DNA fingerprinting is a technique for identifying and analysing differences in DNA between individuals. It is based on DNA sequence variability and polymorphism. Some of its applications include: In forensic science, it is used to identify prospective criminal suspects. To prove paternity and establish familial ties.

What is the basis of DNA fingerprinting? ›

The basis of DNA fingerprinting is VNTR. VNTR is a satellite DNA as a probe showing a high degree of polymorphism. This implies that there are repetitive sequences of DNA that are found across individuals of all species. Scientists identify variations in these sequences.

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