Fingerprinting: The DNA's Saga

JUST AS YOUR FINGERPRINTS TELL YOU A STORY, SO DOES YOUR DNA

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

DNA Fingerprinting was developed by Dr. Alec Jeffreys in 1984. UK police accepted his help in verifying a suspect's confession, and he was subsequently held responsible for two rape-murders. The tests showed that the suspect did not commit the crime. Dr. Lalji Singh worked in the field of DNA Fingerprinting technology and hence is known as the father of DNA Fingerprinting in India.

DO U KNOW MOST OF OUR DNA IS JUNK?

Oh my god! DNA which is also known as the genetic blueprint is of no use. Do you know only 2% of human DNA(also called coding regions) is responsible for characteristic features like hair color, eye color, skin tone etc? The remaining 98% of DNA is junk (called non-coding regions).

The human genome contains numerous small non-coding regions/sequences that are inheritable and present in our genome in the form of multiple repeats.

These small non-coding repeated sequences are used in the DNA Fingerprinting technique.

The era of organism identification, characterization, and classification was transformed by DNA fingerprinting technique.

PRINCIPLE OF DNA FINGERPRINTING: DNA AS A PROBLEM-SOLVING TOOL

Non-coding regions are also called Satellite DNAs and show polymorphism which is the basis of DNA Fingerprinting. These repeated regions can be divided into groups based on the size of the repeat: variable number tandem repeats(VNTRs) and short tandem repeats(STRs). These repeats are able to act as genetic markers, and every individual inherits these repeats from their ancestors, particularly parents. So we can say that every individual has a unique composition of VNTRs. This constitutes the main principle behind all DNA fingerprinting techniques.

Forensic scientists use these VNTRs and STRs to differentiate one person from another and define the DNA profile of an individual.

But it should be noted that all cells except RBCs contain DNA. So sweat, semen, or skin cells that are left behind at a crime scene can be used to identify the number of tandem repeats which help in finding the criminals more conveniently.

An interesting fact; no two individuals have matching STR markers except in the case of twins!

DO YOU KNOW HOW DNA FINGERPRINTING WORKS?

1. Sample Collection: The very first step is sample collection. DNA samples are collected from blood, saliva, skin, hair, etc.

2. DNA Extraction: For performing DNA Fingerprinting we first need to isolate the DNA from our collected sample. High quality and quantity of DNA increases the possibility of getting better results.

These days, forensic scientists use three main methods to extract the DNA ;

● Phenol-chloroform DNA extraction strategy

● CTAB DNA extraction strategy

● Proteinase K DNA extraction strategy

However, for DNA fingerprinting, scientists strongly advise using a ready-to-use DNA extraction kit. To conduct the DNA test, the purity, and quantity of DNA must be ～1.80 and >100ng, respectively. If necessary, DNA sanitization equipment to filter the DNA is also used. From that point on, they use the UV-visible spectrophotometer to quantify the DNA. Additionally, implement one of the supporting techniques listed below.

3. Restriction Absorption, Enhancement, or DNA Sequencing: What technique should be used depends on what assay we are performing. For instance, for detecting maternal cell contamination, PCR-based gel electrophoresis is used. Whereas, capillary gel electrophoresis and rt-PCR is used for forensic analysis. (remember the rt-PCR test for covid? That’s a form of DNA Fingerprinting too!)

Three regular strategies are utilized:

i) RFLP-based STR investigation

ii) PCR-based investigation (PCR agarose gel electrophoresis)

iii) Real-time PCR investigation

iv) Capillary electrophoresis

4. Analysis and interpretation of result: Various analysis processes have been developed by scientists and the analysis process used varies from technique to technique.

To expand, we can say that information about the differences and similarities between people can be learned by comparing the DNA profiles of different samples. Notably, the entire procedure is now practically automated. Therefore, since the computer provides the final output, human labour is not required.

WHAT IS DNA FINGERPRINTING USED FOR?

● DNA profiling or fingerprinting is usually used for official and legal purposes like criminal investigations, sexual assaults, etc. but nowadays this process has become extremely useful in parentage testing( to confirm parental and child status between individuals. Thanks to DNA Fingerprinting criminal cases are solved easily!

● The ability of DNA fingerprinting to identify blood relatives, such as siblings and close grandparents or grandchildren, has also proven useful. Could you imagine, now you can find your distinct relative just by providing your tissue sample?

● It is utilized to detect maternal cell contamination. The term might look complex but it is not. Let's find out more about it!

Maternal cell tainting is one of the main drawbacks of prenatal diagnosis. Sometimes, maternal DNA or tissue can be found in the amniotic fluid or CVS test. The possibility of false-positive results increases with contamination, especially because of carrier identification. During pregnancy hereditary testing, maternal cell tainting can be identified using VNTRs and STRs markers with PCR-gel electrophoresis.

● You must have seen articles in newspapers about missing dead bodies. Well DNA fingerprinting has come to an aid !! We can utilize this technique to identify those missing bodies now.

DNA FINGERPRINTING IN THE MEDICAL FIELD

● Did you know the organ transplant procedure utilizes this technique?? It helps doctors match the tissues of organ donors with patients who need transplants.

● It also helps in tracking down any hereditary condition in the family. Additionally, DNA fingerprinting makes it simpler for doctors to suggest a course of therapy for an illness.

DNA fingerprinting is one of the most advanced technologies for identifying and linking individuals to each other or a particular situation. It is a very accurate method and gives extremely accurate genetic testing and forensic science results. This method is of utmost importance these days as scientists are developing more reliable and cheaper ways to perform it.

Author: Saloni Vohra Editor: Sanskriti Nayyar Illustration: Bristi Paul