Model Answer
0 min readIntroduction
DNA fingerprinting, also known as DNA profiling, is a laboratory technique used to establish a link between biological evidence and a suspect in a criminal investigation or to establish paternity. Developed by Sir Alec Jeffreys in 1984 at the University of Leicester, it revolutionized forensic science and has become an indispensable tool in various fields, including criminal justice, paternity testing, and species identification. The technique relies on variations in individuals’ DNA sequences, specifically repetitive sequences, to create a unique genetic profile. This profile acts like a ‘fingerprint’ specific to each individual (except identical twins).
The Process of DNA Fingerprinting
The process of DNA fingerprinting involves several key steps:
1. DNA Extraction
The first step involves isolating DNA from a biological sample such as blood, saliva, hair follicles, semen, or tissue. This is typically achieved through cell lysis, followed by purification of the DNA.
2. DNA Amplification (PCR)
Due to the often limited amount of DNA available, a technique called Polymerase Chain Reaction (PCR) is used to amplify specific regions of the DNA. PCR creates millions of copies of the target DNA sequence, making it sufficient for analysis. Specific primers are designed to flank the regions containing VNTRs.
3. DNA Fragmentation & Separation
The amplified DNA is then cut into fragments using restriction enzymes. These enzymes recognize and cut DNA at specific sequences, creating fragments of varying lengths. The fragments are then separated based on their size using a technique called gel electrophoresis. In gel electrophoresis, DNA fragments are loaded into a gel matrix and an electric field is applied. Smaller fragments migrate faster through the gel than larger fragments, resulting in a separation of fragments by size.
4. Detection & Visualization
Finally, the separated DNA fragments are visualized. Historically, radioactive probes were used, but now non-radioactive methods like chemiluminescence or fluorescence are more common. This creates a pattern of bands, representing the DNA fingerprint. The pattern is unique to each individual (except identical twins).
Identifying the Key Component: VNTRs
The question asks which of the listed options is used in DNA fingerprinting. The correct answer is (ii) V.N.T.R (Variable Number Tandem Repeats). Let's examine why:
- V.N.T.R.s: These are repetitive DNA sequences that vary in number between individuals. The number of repeats at a particular VNTR locus differs significantly from person to person, making them highly informative for individual identification. These variations are inherited, and thus can be used for familial relationship analysis.
- Palindromic sequences of DNA: While important for restriction enzyme recognition sites, they don't provide the variability needed for individual identification. They are present in all individuals.
- Shine-Dalgarno sequences: These are sequences found in prokaryotic mRNA and are involved in ribosome binding during protein synthesis. They are not relevant to DNA fingerprinting in eukaryotes.
- TATA boxes: These are DNA sequences found in the promoter region of genes and are involved in initiating transcription. They are also not used for individual identification.
Modern DNA fingerprinting often utilizes Short Tandem Repeats (STRs) instead of VNTRs. STRs are shorter and more easily amplified by PCR, making them more suitable for automated analysis and high-throughput applications. However, the underlying principle remains the same – exploiting variations in repetitive DNA sequences.
| Feature | VNTRs | STRs |
|---|---|---|
| Length | Longer (10-100 base pairs) | Shorter (2-6 base pairs) |
| Amplification | Difficult to amplify | Easily amplified by PCR |
| Automation | Less suitable for automation | Highly suitable for automation |
| Frequency of Variation | Highly polymorphic | Highly polymorphic |
Conclusion
In conclusion, DNA fingerprinting is a powerful technique based on the unique variations in individuals’ DNA, particularly in repetitive sequences like VNTRs (and increasingly, STRs). The process involves DNA extraction, amplification, fragmentation, separation, and detection, ultimately generating a unique genetic profile. This technique has revolutionized forensic science and continues to be a vital tool in various applications, from criminal investigations to paternity disputes and beyond. The ongoing advancements in DNA sequencing technologies are further enhancing the accuracy and efficiency of DNA fingerprinting.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.