Introduction
It is technique used for determining nucleotide sequences of certain areas of DNA which are unique to each individual. DNA fingerprinting can distinguish one human being from another with the exception of monozygotic twins, 99.9 percent of base sequence. The differences occur not only in genes but also in repetitive DNA
DNA fingerprinting involves identifying differences in some specific regions in DNA sequences called as repetitive DNA. These repetitive DNA are separated from bulk genomic DNA as different peaks during density gradient centrifugation. The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA. Satellite DNA is classified into following categories on the basis of base composition (A;T rich or G; C rich), length of segment and number of repetitive units.
These categories are:-
VNTRs (Variable Number of Tandem Repeats) or minisatelites surrounded by conserved restriction sites. A small DNA sequence is arranged tandemly in many copy numbers. The copy numbers varies from chromosome to chromosome in an individual. The number of repeats show very high degree of polymorphism. As a result the size of VNTR varies from 0.1 to 20 kb.
SSRs (Single Sequence Repeats) or STRs (Short Tandem Repeats) or microsatellites with 1-6 bp.
These sequences normally do not code for any proteins, but they form a large portion of human genome. These sequences show high degree of polymorphism and form the basis of DNA fingerprinting.
Polymorphism is the variation at genetic level. Since DNA from every tissue (such as blood, hair-follicle, skin, bone, saliva, sperm etc), from an individual show the same degree of polymorphism, they become very useful identification tool ii forensic applications. Further, as the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing, in case of disputes.
As polymorphism in DNA sequence is the basis of genetic mapping of human genome as well as of DNA fingerprinting. It is essential that we understand that what DNA polymorphism means is simple terms.
Polymorphism (variation at genetic level) arises due to mutations. Allelic sequence variation has traditionally been described as a DNA polymorphism if more than one variant (allele) at a locus occurs in human population with frequency greater than 0.01.
In simple terms, if an inheritable mutation is observed in a population at high frequency it is referred to as DNA polymorphism. The probability of such variation to be observed in non-coding DNA sequence would be higher as mutations in these sequences may not have any immediate effect in an individual reproductive ability.
These mutations keep on accumulating generation after generation and form one of the basis of variability/polymorphism. There is a variety of different types of polymorphisms ranging from single nucleotide change to very large scale changes. For evolution and sepeciation, such polymorphism play very important role
Thus, the basis of DNA fingerprinting is VNTR (a satellite DNA as probe that shows very high degree of polymorphism). The technique of DNA fingerprinting was developed by Alec Jeffreys. The technique, as used earlier, involved Southern blot hybridization using radiolabelled VNTR as probe.
It is included:-
(i) Isolation or DNA,
(ii) Digestion of DNA by restriction endonucleases.
(iii) Separation of DNA fragments by electrophoresis , or (RFLP Restriction Fragment Length polymorphism).
(iv) Transferring (blotting) of separated DNA fragment to synthetic membranes, such as nitrocellulose or nylon.
(v) Hybridisation using labeled VNTR probe.
(vi) Detection of hybridized DNA fragments by autoradiography
After hybridization with VNTR probe, the autoradiogram gives many bands of different sizes, These bands give a characteristic pattern for an individual DNA.
The sensitivity of the technique has been increased by use of polymerase chain reaction (PCR), Consequently, DNA from a single cell is enough to perform DNA fingerprinting analysis.
Practical Applications :-
Paternity-maternity disputes
2. criminal identification and forensics
Personal identification
Close relations of an intending immigrant.
Note:- Lalji Singh and V.K Kashyap are Indian experts in the field of DNA fingerprinting.
DNA fingerprinting, also known as DNA profiling, is a forensic technique used to identify individuals by characteristics of their DNA. It involves analyzing specific regions of the DNA that are highly variable among individuals, known as variable number tandem repeats (VNTRs) or short tandem repeats (STRs). These regions create a unique pattern for each individual, much like a fingerprint, hence the term “DNA fingerprinting.”
The process of DNA fingerprinting involves several steps:
Sample Collection: DNA is collected from biological samples such as blood, hair, saliva, or skin cells.
DNA Extraction: DNA is extracted from the collected cells.
DNA Digestion: The extracted DNA is cut into fragments using restriction enzymes.
Gel Electrophoresis: The DNA fragments are separated by size using gel electrophoresis.
Southern Blotting: The DNA fragments are transferred to a membrane and then exposed to DNA probes that bind to specific sequences.
Visualization: The pattern of DNA fragments is visualized, usually using X-ray film, resulting in a unique DNA profile for each individual.
DNA fingerprinting has several important applications, including:
Forensic Science: Identifying suspects or victims in criminal investigations.
Paternity Testing: Determining biological relationships.
Medical Research: Identifying genetic disorders or variations.
Conservation Biology: Monitoring genetic diversity in wildlife populations.
Historical Investigations: Resolving historical or archaeological mysteries involving human remains.
DNA fingerprinting is highly reliable due to the unique nature of individual DNA profiles. The likelihood of two individuals having identical DNA profiles (except for identical twins) is extremely low. Advances in technology and methods have further increased the accuracy and reliability of DNA fingerprinting, making it a trusted tool in forensic science and other applications. However, proper sample collection, handling, and analysis are crucial to avoid contamination and ensure accurate results.
Yes, there are several ethical concerns, including:
Privacy: The potential for misuse of genetic information, leading to privacy violations.
Consent: The need for informed consent when collecting DNA samples.
Discrimination: The risk of genetic discrimination in employment, insurance, and other areas.
Data Security: Ensuring the secure storage and handling of genetic data to prevent unauthorized access.
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