Which of these technique is used in DNA fingerprinting?

Question

Accepted Answer

The correct option is 4:
The correct option is 4: All options are correct. DNA fingerprinting, also known as DNA profiling, is a powerful technique for identification that is fundamentally based on the unique genetic make-up of an individual. The three concepts listed—Repetitive DNA, Polymorphism in DNA, and Variable Number of Tandem Repeats (VNTR)—are not separate techniques but rather represent the *three core biological principles* that the method relies upon. Firstly, the technique exploits **Polymorphism in DNA** (Option 2), which is the variation in DNA sequences among individuals. These differences are what make each person's DNA unique and identifiable. Secondly, the specific regions targeted for profiling are found within the vast expanse of **Repetitive DNA** (Option 1). These are non-coding sequences that make up a large portion of the genome, and because they are not under intense selective pressure, they accumulate mutations and variations at a much higher rate than gene-coding regions. Finally, the most common and highly variable form of this repetition used in the classic fingerprinting technique (developed by Sir Alec Jeffreys) are the **Variable Number of Tandem Repeats (VNTRs)** (Option 3). VNTRs are short sequences of DNA organized as a tandem cluster, where the *number* of copies of the repeat unit differs from person to person and is inherited in a Mendelian fashion. The analysis of these three features—Polymorphism (the variation), Repetitive DNA (the location), and VNTR (the form of variation)—is what generates the unique "fingerprint," making option 4 the only answer that fully encompasses the biological foundation of the entire process.

The incorrect option is 1:
The incorrect option is 1: Repetitive DNA. While it is true that the DNA sequences used in fingerprinting are a specific type of repetitive DNA, stating that "Repetitive DNA" is the *entire technique* is incomplete and thus incorrect. Repetitive DNA sequences are present across the entire human genome in many forms, some of which are not highly polymorphic or useful for individual identification. This option only identifies the *type of sequence* analyzed, but fails to capture the essential concepts of individual variation (polymorphism) and the specific nature of the repeat variation (VNTR) that the process exploits. Simply put, not all repetitive DNA is used for fingerprinting, only the highly variable segments.

The incorrect option is 2:
The incorrect option is 2: Polymorphism in DNA. DNA polymorphism, which simply means differences in the DNA sequence between individuals, is the *theoretical basis* of DNA fingerprinting. However, this term is too broad to stand as the sole correct answer. Polymorphism can be caused by single nucleotide variations (SNPs), deletions, or insertions, many of which are not suitable for the standard multi-locus probe or PCR-based fingerprinting methods. The technique specifically leverages the polymorphism found in repetitive sequences, which are the highly efficient markers. Choosing only "Polymorphism in DNA" ignores the crucial detail of *which kind* of polymorphism is targeted for the test's efficacy.

The incorrect option is 3:
The incorrect option is 3: Variable no. of Tandem repeats. Variable Number of Tandem Repeats (VNTRs) represent the highly specific, usable markers that are detected to generate the profile. This is arguably the most *precise* component of the technique, as the differing number of repeats is what provides the variability for distinguishing individuals. These sequences, once isolated, are analyzed using techniques like Southern blotting. However, even this term is a type of Repetitive DNA and a source of DNA Polymorphism; therefore, it does not fully describe the broader genetic context of the technique. Choosing only "VNTR" ignores the overarching biological concept of polymorphism in the genome, which is the foundational reason the technique works in the first place.