Motivational speeches from many corners of the world emphasize on uniqueness of an individual through phrases like “you are unique, therefore you are special” and “there is no one else like you”. Not only do these statements hit correct notes on an aesthetic level but scientific studies back it up as well. The code in our DNA contains a unique code that no one else on earth shares. A drop of our blood or just a single strand of our hair is enough to identify us without any mistakes. This scientific breakthrough has been made through DNA fingerprinting.
DNA fingerprinting is a popular molecular biology technique used to identify individuals on the basis of their unique patterns of DNA. Humans share about 99.9% of their genetic code.1 However the remaining 0.1% of DNA is made up of a series of identical sequences called repetitive DNA or tandem repeats, which are highly variable regions. The pattern, length, and number of these repeats have been observed to be unique for each individual and are used for identifying an individual. This very concept is the foundational principle behind DNA fingerprinting technique.
1.1 History
DNA fingerprinting was discovered in 1984 by Alec Jeffery. He was a British geneticist at the University of Leicester.1 In his process of studying the evolution of genes, Jeffery accidentally found out that certain regions in DNA made up of repeated units of 10 – 60 base pairs, known as minisatellites varied significantly among individuals, even within the same family. He discovered that these variations could be used to create a unique genetic profile for every individual.
In the mid-1980s, DNA fingerprinting started being used in criminal investigations, more particularly to identify perpetrators behind crimes like rape and murder. It also gained popularity by its usage in immigration cases, which involved the determination of relationships or paternity tests. Later in the 1990s, many further techniques were developed to make the process of DNA fingerprinting faster and more precise. Polymerase Chain Reaction (PCR) allowed DNA analysis from tiny or degraded DNA samples. Later, various DNA databases and automated DNA sequencing techniques were developed. These added modern techniques made DNA fingerprinting faster, more precise, and accessible to a wider audience.
1.2 Genetic basis behind DNA fingerprinting
DNA is made up of nucleotides. A nucleotide is composed of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (A, T, G or C). These sequences of DNA bases carry genetic information which are transferred from one generation to next. 99.9% of human DNA is common across all individuals, the remaining 0.1% contains regions having high variability.2 These variable genes are generally of two types:
VNTRs (Variable Number Tandem Repeats)
It includes longer repeating sequences of about 10-20 base pairs. Jefferys used VNTRS to develop the first DNA fingerprints.
STRs (Short Tandem Repeats)
These include shorter repeating sequences of 2-6 base pairs. It is now considered standard region used for DNA fingerprinting due to its ease of amplification and high variability.2
1.3 Process of DNA fingerprinting
Jefferys initially developed a series of DNA probes which are short pieces of DNA that seek out any specific sequences they match. The probe then base pairs with the selected complementary sequence. Such molecular probes are used to detect the unique repetitive patterns in DNA which is characteristic of each individual. In general, the DNA fingerprinting technique follows the following procedure:
1. Purified DNA is obtained from small samples of blood, hair strands, semen, skin, saliva, or other DNA-bearing cells.
2. Specific regions (mostly STRs) are amplified using PCR. PCR is a popular molecular biology technique that can create millions of copies of a small DNA segment. This process may prove essential if the samples are small in quantity or degraded.1
3. The amplified DNA fragments are separated by size using agarose gel electrophoresis or capillary electrophoresis (more modern approach)
4. The result appears in a pattern of bands (in gels) representing the number of repeats at each STR locus. Forensic panel examines about 13-20 STR loci for a highly specific genetic profile.
5. The genetic profiles from samples collected are compared to the known genetic profiles of individuals and analyzed. If the band patterns at all tested loci are identical, it is considered to be a match.
1.4 Application of DNA fingerprinting
DNA fingerprinting has acclaimed widespread usage in various fields. Some of them are as follows:
Forensic science
DNA samples or fingerprints obtained from a crime scene can be compared with DNA fingerprinting from cells provided by the suspect. This can make crime investigation rapid and more valid. It can also be used to identify victims, especially during natural disasters like wildfire and flooding where it would be difficult to identify the victim otherwise.
Paternity testing and relationship determination
DNA fingerprinting can be used to establish biological connections between individuals including paternity testing. It is widely used in immigration offices to validate the identity status of an individual.
Medical research
DNA fingerprinting is used in various genetic research which may involve gene tracking or analysis of genetic disorders. This could be used to predict the probability of an individual inheriting the genetic disease which gives the benefit of time to plan treatment options.
Wildlife conservation biology
DNA fingerprinting helps to track the status of endangered species and prevents poaching of endangered wildlife. It also aids in making relevant plans and policies to conserve and safeguard wildlife.
1.5 Disadvantages and Legal Concerns
1. DNA samples can get easily contaminated at the crime scene or during laboratory testing. Even a small amount of foreign DNA can give misleading results.
2. Damaged or old samples may not provide reliable genetic profiles.
3. DNA fingerprinting requires specialized equipment and highly skilled personnel which may be an issue in underdeveloped settings.
4. Misuse of data collected through DNA fingerprinting can pose a serious threat to an individual’s identity and privacy. It may raise issues such as genetic discrimination or ethnic bias.
5. Monozygotic twins known as identical twins cannot be detected by this technique since they share the same STR patterns which are used in standard DNA fingerprinting.
Reference
1. Dr. P.S. Verma, Dr. C.K. Agrawal. Cell Biology, Genetics, Molecular Biology, Evolution and Ecology. fourteenth. (Bharatnagar S, Pradhan S, eds.). S.CHAND & COMPANY PVT.LTD.; 2016.
2. Watson J.D., Baker T.A., Bell S.P., Gann A, Levine M. Molecular Biology of the gene. Seventh. Pearson; 2014
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