DNA Fingerprinting: Do you ever realise how the cops get hold of the criminals at the murder site? This is done by DNA fingerprinting. DNA fingerprinting is a process that evaluates the probable identity of a person by determining the variations of nucleotide sequences. This process is usually done by matching the nucleotide sequences which are unique to humans. The other names of DNA fingerprinting are DNA typing, DNA profiling, genetic fingerprinting, genotyping, or identity testing.

In this article, students will learn about the detailed procedure of DNA fingerprinting and how it is done. It will also describe the importance and principle along with the uses of DNA fingerprinting or DNA profiling which is known to be an important concept for all CBSE Class 12 Biology students. Read through the article to find out more interesting details!

What is DNA Fingerprinting?

DNA Fingerprinting is a technique that is used to determine the nucleotide sequences of repetitive areas of DNA which are unique to each individual. It is also called DNA profiling or DNA typing.

Who Developed DNA Fingerprinting?

The science of DNA Fingerprinting was first used by Sir William Herschel as a method of identification in 1858. Dr. Alec Jeffreys in 1984 invented the DNA fingerprinting technique at the University of Leicester in the United Kingdom to identify the DNA sequences found between the genes to identify the markers for inherited disease so that they can be treated early. At that moment he had no idea the same technique would help to solve the murder cases or paternity cases later. Later, Dr. V.K. Kashyap and Dr. Lalji Singh started the DNA fingerprinting technology in India at CCMB (Centre for Cell and Molecular Biology), Hyderabad.

NCERT Solutions 12th Biology Chapter 6

Do you Know?
Father of DNA Fingerprinting- Dr. Alec Jeffreys
Father of Indian Fingerprinting- Dr. Lalji Singh

Basics of DNA Fingerprinting

Below we have provided detailed information on important terms related to DNA fingerprinting:

1. Repetitive DNA: These are the regions of the DNA in which small stretches of DNA sequences are repeated many times.
2. Satellite DNA: These are the regions of the DNA that normally do not code for any proteins but they form a large part of the human genome. These sequences show a high degree of polymorphism and form the basis of DNA fingerprinting.
3. Polymorphism: It refers to the variations at the genetic level that arise due to mutations. DNA polymorphism plays a very important role in evolution and speciation.  The frequency of such polymorphism is greater than 0.01.
4. Variable Number of Tandem Repeats (VNTR): VNTR belongs to a class of satellite DNA referred to as minisatellite. VNTR shows a very high degree of polymorphism. A small DNA sequence is arranged tandemly in many copy numbers. The copy numbers vary from chromosome to chromosome in an individual. As a result, the size of VNTR varies from 0.1 to 20 kb.
5. Single Nucleotide Polymorphisms (or SNPs): SNPs are variations in a DNA sequence that occur when a single nucleotide in the sequence is different from the normal in at least one percent of the population. There are about 1.4 million SNPs in the human genome.
6. Microsatellites: These are the repetitive DNA sequences usually several base pairs in length composed of non-coding DNA and are not part of genes. They are used as genetic markers to follow the inheritance of genes in families. SSRs (Single Sequence Repeats) or STRs (Short Tandem Repeats) or microsatellites have repeats of about 1 -6 bp.

Principle of DNA Fingerprinting

The principles of DNA fingerprinting are mentioned below:

1. DNA fingerprinting or DNA profiling identifies the combination of DNA sequences which tend to vary greatly between individuals.
2. The most important requirement for DNA fingerprinting is short nucleotide repeats that vary in number from person to person but are inherited. These are called variable number tandem repeats or VNTRs. 
3. The DNA fingerprinting technique is based on the theory that except for identical twins (monozygotic twins), no two people possess identical DNA sequences.

Process of DNA Fingerprinting

The techniques of DNA fingerprinting are as follows:

1. DNA fingerprinting is a method to analyse DNA found in biological materials.
2. It is done by Restriction Fragment Length Polymorphism (RFLP).
3. In RFLP, DNA is first extracted from the cell and then divided into fragments by restriction enzymes.
4. Following are the steps involved in DNA fingerprinting:
a. Isolation of DNA- In this, DNA is extracted from the cell and purified by chemical treatment and centrifugation.
b. Amplification- A number of copies of the extracted DNA are made by a technique called polymerase chain reaction (PCR).
c. Digestion of DNA by restriction endonuclease enzyme- The DNA is cut into fragments with the help of the restriction endonuclease enzyme. These enzymes snip the DNA at specific places and DNA is chopped up into varying lengths.
d. Separation of DNA- The DNA fragments are then separated by a technique called electrophoresis, according to their size.
Electrophoresis is a method used to separate charged molecules in the presence of an electric field. During electrophoresis, fragments of DNA are placed on a bed of clear gel on a plate and then an electric current is applied to it. Since DNA fragments have a single negative charge, they move towards the positive electrode. Eventually, the fragments get deployed at various spots along with the gel according to their size.
e. Then the chemicals are added that split the DNA fragments into single strands.
f. Transferring (blotting) of the separated DNA fragments from the gel on synthesis membranes like nitrocellulose or nylon- The separated DNA fragments are then transferred from the gel to a nylon membrane or nitrocellulose and this technique used is called Southern blotting. In this technique, the gel is covered with a nylon membrane that draws the bits of DNA onto the nylon, just like drying wet ink with the blotting paper.
g. Hybridisations using radiolabeled probes- In this step, the DNA fragments are tagged with the radioactive isotope by hybridization, so that their position can be detected by an X-ray film. This is done by putting a nylon membrane into a bath containing probes (probes are short pieces of single standard complementary DNA, tagged with radioactivity that bind to a specific chain of DNA VNTR sequences according to the base-pairing rule).
h. Detection of hybridised DNA fragments (Autoradiography)– In this step, the membrane is exposed to the X-ray film to get an autoradiograph which when developed, reveals a unique pattern of light and dark bands that reflect the composition of DNA. The dark bands on the X-ray film represent the DNA fingerprints.

Fig: Steps in DNA Fingerprinting

Applications of DNA Fingerprinting

The applications of DNA fingerprinting are as follows:
1. Individuality– It helps to differentiate one human being from another with the exception of monozygotic twins.
2. Paternity or Maternity Disputes– It helps to find out the real genetic mother, father and offspring.
3. Human Lineage– It is also used to study human lineages.
4. Hereditary Diseases– It is used to identify genes connected with hereditary diseases.
5. Forensics– It is very helpful in the detection of crime and legal pursuits.
6. Sociology– It helps to identify racial groups, their origin, historical migration and invasions.

Summary

DNA Fingerprinting is a technique that is used to find out the nucleotide sequences of certain areas of DNA which are unique to each individual. The other names of DNA fingerprinting are DNA profiling, genetic fingerprinting, identity testing, genotyping, forensic genetics or DNA typing. We all know the fact that no two individuals, except monozygotic twins, are identical in this world.

Every individual has a unique DNA fingerprint. The most important requirement for DNA fingerprinting is short nucleotide repeats that vary in number from person to person but are inherited, i.e, VNTRs. DNA fingerprinting helps to distinguish one human being from the other, solve maternity and paternity disputes, and criminal cases, find out the cause of hereditary diseases, etc.

FAQs on Process of DNA Fingerprinting

Q.1: What is the principle of DNA fingerprinting?
Ans: The most important requirement for DNA fingerprinting is short nucleotide repeats that vary in number from person to person but are inherited. These are called variable number tandem repeats or VNTRs and this is the main principle of DNA fingerprinting.

Q.2: What are the six steps of DNA fingerprinting?
Ans: 1. Isolation of DNA.
2. Amplification of DNA and cutting the DNA into small fragments.
3. Separation of DNA fragments by gel electrophoresis.
4. Transferring separated DNA fragments onto the synthesis membrane.
5. Hybridisation using radiolabeled probes.
6. Detection of hybridised DNA fragments.

Q.3: What are the applications of DNA fingerprinting?
Ans: 1. It helps to distinguish one human being from another with the exception of monozygotic twins.
2. It helps to identify the real genetic mother, father and offspring.
3. It is also used to study human lineages.
4. It is used to identify genes connected with hereditary diseases.

Q.4: Who is the father of DNA fingerprinting?
Ans: Dr. Alec Jeffreys is called the father of DNA fingerprinting.

Q.5: Why is it called DNA fingerprinting?
Ans: A DNA fingerprint is a DNA pattern that has a unique sequence such that it can be distinguished from the DNA patterns of other individuals.

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