DNA Fingerprinting Technology: Steps, Types & Applications

DNA fingerprinting, also known as DNA profiling, is a molecular method that is used for identifying an individual through analysis of highly variable segments in his/her DNA. DNA profiling typically includes sample collection, isolation of DNA from samples, amplification via PCR, separation/detection of DNA markers, profiling and comparison with database profiles. STR is the current tool for forensic profiling, while mitochondrial DNA and SNP analysis could be helpful in analyzing difficult samples.

Uses of DNA-forensic technology include but not limited to criminal investigation, paternity testing, identification of disaster victims and wildlife forensic cases. India is building its DNA-forensic infrastructure by modernizing its DNA labs at state FSLs and setting up new forensics labs. Rapid DNA technologies have been developed for automated DNA profiling.

• DNA Fingerprinting is one forensic tool that is commonly used for identifying persons based on their DNA patterns.
• A complementary point here is that each individual, except a set of identical twins, has unique DNA composed of different-combination nucleotide sequences.
• From its forensic uses of crime-solving, paternity determination to unknown human remains identification, DNA fingerprinting has many applications.

Here is a DNA Fingerprinting process:

• Sample Collection: A biological sample from the crime scene or the individuals involved or any other relevant source is collected. Blood, saliva, semen, hair, and tissues are common types of samples.
• DNA Extraction: To extract the DNA, an appropriate technique is selected according to the nature of the sample. In general, a cell lysis procedure to separate the DNA from cells and protein digestion with protease enzymes to remove contaminating proteins are applied. Extracted DNA is usually in a mixture with other cell components.
• DNA Purification: The isolated DNA undergoes purification to eliminate contamination from proteins, etc. This purification provides clean DNA that is very important in further analysis.
• Polymerase Chain Reaction: Here, certain short regions of DNA known as short tandem repeats (STRs) or variable number tandem repeats (VNTRs) are targeted for selective amplification. These regions are highly polymorphic. Hence the differences between two or more individuals in these regions are measured by PCR. Even if a small amount of DNA or degraded DNA is left, PCR can still amplify the DNA.
• Gel Electrophoresis: This technique is used to separate DNA of varying length after it has been amplified through the process of PCR.
• A gel containing tiny pores separates the DNA fragments based on their length. Smaller fragments move faster through the gel, while larger fragments move more slowly.
• DNA Visualization: After electrophoresis, the DNA fragments separated are visualised by radiation techniques or stains (e.g., ethidium bromide).
• The fragments thus make up a pattern of bands on the gel.
• Pattern Analysis: The DNA-fragment pattern, often called the DNA "fingerprint," is analysed.
• The number and size of the fragments at particular STR loci are compared between unknown samples and reference samples of the known identity (e.g., suspects or victims).
• Matching: A positive match occurs whereby the DNA fingerprint from an unknown sample coincides with the DNA fingerprint of a known individual.
• The result can thus be utilised in criminal investigations, paternity, and other cases.
• Statistical Analysis: Statistics are indeed calculated to show the strength of the match, enabling one to express association in terms of the likelihood of the two DNA profiles being contributed by either the same individual or unrelated individuals.

There are various kinds of DNA profiling methods which depend on the kind of DNA marker being analyzed and the method used for profiling DNA. Some of the main DNA fingerprinting methods include:

Restriction Fragment Length Polymorphism (RFLP):

An old technique of DNA profiling which entails analyzing the different lengths of DNA fragments after DNA has been cleaved using restriction enzymes. Requires large quantities of DNA.

DNA Fingerprinting Using PCR (Polymerase Chain Reaction):

This entails using Polymerase Chain Reaction to copy certain DNA segments from either large or degraded samples and is thus important for forensic purposes.

STR (Short Tandem Repeat) Analysis:

Entails analysis of highly variable DNA repeats. This is the method used for modern day DNA profiling for forensic purposes.

MtDNA Profiling (Mitochondrial DNA Profiling):

Analysis of DNA passed on through maternal ancestry. Important for analyzing degraded DNA, hair shafts and other old remains.

Y-Chromosome DNA Profiling:

Analysis of DNA markers on the Y chromosome that are passed through paternity line. This is important in male lineage research.

SNP Analysis (Single Nucleotide Polymorphism):

Analysis of single nucleotide variations in DNA. SNP analysis may be applied for degraded DNA samples, ancestry research and more advanced forensics.

The application of DNA Fingerprinting can be seen as follows:

• Criminal Investigations: DNA fingerprinting is frequently used, in criminal justice, to link suspects to crime scenes or to exclude innocents. It can identify perpetrators of crimes such as murder, sexual assault, burglary, and kidnapping.
• Paternity Testing: Such testing determines such fatherhood and motherhood through the DNA fingerprinting technique. This is crucial when up for child custody rights and inheritance matters, and it establishes responsibilities legally.
• Missing Persons and Unidentified Remains: DNA profiling identifies missing persons in cases of accidents, natural disasters, or criminal cases. It may assist in identifying remains in mass graves or long-identified deceased individuals.
• Immigration and Citizenship: DNA fingerprinting can establish biological relationships in immigration cases whereby individuals seek to join their family members in another country or to endeavor to gain citizenship with regard to family ties.
• Forensic Genealogy: Advances in DNA fingerprinting methods, now aided by genealogical databases, have become a solution to tracing distant relatives in cold cases and, thereby, in many cases, identifying suspects or victims.
• Conservation of Wildlife: Attaining DNA profiles is taken into consideration while studying and surveying wildlife populations, tracing the illegal trade of endangered species, and combating poaching. It helps to identify individuals within a species so as to conserve them, measure genetic variation, and recommend conservation plans.
• Farming and Animal Husbandry: Agricultural DNA fingerprinting aids food authentication in its simplest form, detection of food fraud, and tracing of livestock for breeding and quality evaluation assignment purposes.
• Historical and Anthropological Research: DNA fingerprinting aids in studying ancient DNA to establish human migration patterns, ancestry, and evolution; it can also be extrapolated into solving historic enigmas and identifying the remains of historians.
• Disaster Victim Identification (DVI): In cases of mass disasters such as an air crash or natural disasters, fingerprinting is used for identifying the victim when there is no chance for other methods (like visuals) being available.
• Genealogical Research: Individuals interested in tracing their ancestry and genealogy can use DNA fingerprinting services to discover their genetic heritage and locate distant relatives.