Which one of the following techniques can be used to establish the paternity of a child ?

1. Basics of DNA and Genetic Material (basic)

Welcome to your first step in mastering Genomics! To understand complex DNA technologies, we must first understand what DNA is: the blueprint of life. At its core, reproduction is about passing on information. This information is stored in Deoxyribonucleic Acid (DNA) molecules found in the chromosomes of a cell nucleus. DNA serves as the master manual for making proteins, which in turn build our bodies and determine our traits.

A fundamental event in reproduction is DNA copying. When a cell prepares to divide, it uses biochemical reactions to create a mirror copy of its genetic code. However, DNA cannot survive in a vacuum; it requires a cellular apparatus (like ribosomes and mitochondria) to function. Therefore, DNA copying is always accompanied by the creation of an additional cellular structure so that when the cell divides, each new DNA copy has its own "life support system" Science, Class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.114. Because biochemical reactions are never 100% accurate, small "errors" occur during this copying process. These variations are the raw material for evolution—while drastic changes might lead to cell death, subtle variations allow species to adapt over generations Science, Class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.114.

In complex organisms, the strategy of sexual reproduction allows for the combination of DNA from two different individuals. This creates a logical puzzle: if two cells fuse, shouldn't the child have double the DNA? Nature solves this through a process where specialized reproductive cells (gametes) contain only half the amount of DNA and half the number of chromosomes compared to normal body cells Science, Class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.120. When these two "half-sets" combine during fertilization, the original DNA amount is restored, ensuring the stability of the species' genetic makeup.

Feature	DNA Copying (Mitosis)	Gamete Formation (Meiosis)
Purpose	Growth and maintenance of the organism.	Preparation for sexual reproduction.
DNA Content	Remains the same as the parent cell.	Reduced to half the original amount.
Variation	Minimal (only due to copying errors).	High (combining sets from two parents).

Sources: Science, Class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.113; Science, Class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.114; Science, Class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.120

2. Principles of Heredity and Inheritance (basic)

At its core, heredity is the process by which biological traits are passed from parents to their offspring. This is made possible because both the father and the mother contribute practically equal amounts of genetic material to the child Science, Class X (NCERT 2025 ed.), Heredity, p.129. This means that for every characteristic — whether it’s the shape of your earlobes or the efficiency of a specific enzyme — you carry two versions of the instruction manual: one from your mother and one from your father. These different versions of a gene are known as alleles.

How these two versions interact determines what we actually see in the individual (the phenotype). Gregor Mendel, the father of genetics, discovered that some traits are dominant while others are recessive. If a child inherits two different versions of a gene, the dominant trait is the one that gets expressed, while the recessive trait remains hidden in their genetic code Science, Class X (NCERT 2025 ed.), Heredity, p.133. On a molecular level, this often happens because the "dominant" gene produces a functional protein or enzyme, while the "recessive" gene might produce an altered, less efficient version Science, Class X (NCERT 2025 ed.), Heredity, p.131.

It is also important to understand that traits are generally inherited independently. For instance, the gene determining height does not dictate the gene for seed color or hair texture; they recombine to form new, unique combinations in every generation Science, Class X (NCERT 2025 ed.), Heredity, p.131. A unique application of these rules is sex determination in humans. While females carry two X chromosomes (XX), males carry one X and one Y (XY). Since a mother can only pass on an X, the sex of the child is determined entirely by the father — specifically, whether the sperm that fertilizes the egg carries an X or a Y chromosome Science, Class X (NCERT 2025 ed.), Heredity, p.132.

Sources: Science, Class X (NCERT 2025 ed.), Heredity, p.129; Science, Class X (NCERT 2025 ed.), Heredity, p.131; Science, Class X (NCERT 2025 ed.), Heredity, p.132; Science, Class X (NCERT 2025 ed.), Heredity, p.133

3. Human Genome Project and Mapping (intermediate)

The Human Genome Project (HGP), often hailed as biology's "Moonshot," was a massive international scientific effort (1990–2003) to decode the entire genetic blueprint of a human being. Think of the human genome as a vast library containing 23 volumes (chromosomes), with 3 billion individual letters (base pairs: A, T, C, and G). Before the HGP, we knew the library existed, but we couldn't read the books. The project successfully sequenced nearly 92% of the genome (the rest was completed recently), identifying the location and function of roughly 20,000–25,000 genes.

A critical part of this process is Genome Mapping. While the terms are often used interchangeably, there is a distinct difference between mapping and sequencing:

Feature	Genetic Mapping	DNA Sequencing
Analogy	A highway map showing major cities (landmarks).	A detailed street view showing every single house number.
Purpose	Identifying the relative position of genes on a chromosome.	Determining the exact order of nucleotide bases (A, C, G, T).
Outcome	Helps locate genes associated with specific diseases.	Provides the complete chemical code of the DNA.

In India, the Centre for DNA Fingerprinting and Diagnostics (CDFD) in Hyderabad is a premier institution that applies these genomic principles for forensic investigation and medical diagnostics Environment and Ecology, Majid Hussain, Major Crops and Cropping Patterns in India, p.82. These techniques are not just for humans; they are now used in DNA Barcoding. This technology acts like a "digital tag" for species, allowing scientists to identify organisms quickly. International initiatives like BIOSCAN and the Barcode 500K project are currently building a "library of life" to preserve DNA extracts from all multicellular species for global biosurveillance Environment, Shankar IAS Academy, Conservation Efforts, p.248-249.

By mapping the genome, we move toward Precision Medicine—the ability to tailor medical treatment to the individual genetic profile of each patient. It also raises ELSI (Ethical, Legal, and Social Implications) concerns, such as genetic privacy and the potential for discrimination based on one's "genetic destiny."

Sources: Environment and Ecology, Majid Hussain, Major Crops and Cropping Patterns in India, p.82; Environment, Shankar IAS Academy, Conservation Efforts, p.248-249

4. Applications of Biotechnology in Healthcare (intermediate)

Biotechnology in healthcare, often called 'Red Biotechnology', applies genetic knowledge to diagnose, treat, and prevent diseases. At its core, this field relies on the fact that every individual (except identical twins) possesses a unique genetic code. According to the WHO, Genetically Modified Organisms (GMOs) are those where the DNA has been altered in a way that does not occur naturally Indian Economy, Nitin Singhania (ed 2nd 2021-22), Agriculture, p.301. In medicine, this principle allows us to engineer bacteria to produce human insulin or develop vaccines that are safer and more effective. One of the most powerful applications is DNA Fingerprinting (DNA profiling). This technique has revolutionized forensic science and legal medicine, particularly in establishing biological relationships. Unlike older methods like blood typing, which could only exclude a person (e.g., if a child is Type A and the father is Type B, he might not be the father), DNA fingerprinting can confirm paternity with over 99.9% certainty. It works by comparing Short Tandem Repeats (STRs)—specific locations on the DNA where sequences repeat. Since children inherit half of their genetic material from each parent Science, class X (NCERT 2025 ed.), Heredity, p.131, a child’s STR profile must be a composite of the biological mother's and father's markers.

Feature	Conventional Testing (Blood/Proteins)	DNA Fingerprinting (Profiling)
Accuracy	Low (only for exclusion)	Extremely High (>99.9%)
Sample Source	Fresh Blood	Any nucleated cell (Hair, skin, saliva, blood)
Core Method	Antigen-antibody reactions	PCR, STR analysis, and RFLP
Information	Phenotypic (expressed traits)	Genotypic (direct DNA sequence)

Beyond forensics, biotechnology facilitates biosurveillance and the identification of species through DNA barcoding Environment, Shankar IAS Academy (ed 10th), Conservation Efforts, p.249. By creating a 'library of life,' scientists can quickly identify pathogens or disease-carrying vectors. However, because these technologies involve altering or analyzing the fundamental building blocks of life, they are strictly regulated. In India, the Genetic Engineering Appraisal Committee (GEAC) plays a pivotal role in reviewing the safety of such biological interventions before they reach the public Indian Economy, Nitin Singhania (ed 2nd 2021-22), Agriculture, p.302.

Sources: Indian Economy, Nitin Singhania (ed 2nd 2021-22), Agriculture, p.301-302; Science, class X (NCERT 2025 ed.), Heredity, p.131; Environment, Shankar IAS Academy (ed 10th), Conservation Efforts, p.249

5. Legal and Regulatory Framework for DNA in India (exam-level)

In India, the legal and regulatory framework for DNA technology is a complex mosaic of criminal law, administrative guidelines, and landmark judicial precedents. Currently, India does not have a standalone 'DNA Act,' as the DNA Technology (Use and Application) Regulation Bill, 2019 was officially withdrawn by the government in 2023 due to concerns regarding privacy and the potential for misuse. Consequently, the regulation of DNA is governed by broader statutes. For instance, in the realm of biotechnology and pharmaceuticals, the Modified Drug Policy explicitly mandates that while many sectors enjoy automatic approval for foreign technology, those involving recombinant DNA technology require specific regulatory scrutiny to ensure safety and ethical compliance Geography of India, Majid Husain (9th ed.), Industries, p.62.

The most significant legal guardrail for DNA technology in India is the Right to Privacy. In the landmark case of K.S. Puttaswamy vs. Union of India (2017), the Supreme Court declared privacy to be a Fundamental Right under Article 21 of the Constitution Indian Polity, M. Laxmikanth (7th ed.), Landmark Judgements and Their Impact, p.640. This has profound implications for DNA profiling, as genetic information is the most intimate form of personal data. The court established a 'three-fold test' (legality, necessity, and proportionality) that any state action—such as the mandatory collection of DNA—must satisfy to be constitutionally valid.

In the criminal justice system, the Criminal Procedure (Identification) Act, 2022 (which replaced the century-old Identification of Prisoners Act) now empowers police and investigators to collect 'biological samples,' which includes DNA profiling, from convicts and those arrested for certain offenses. However, the use of DNA in civil cases, particularly paternity disputes, remains cautious. While DNA fingerprinting is scientifically conclusive, Indian courts often balance this against Section 112 of the Indian Evidence Act, which presumes the legitimacy of a child born during a valid marriage. Courts generally order DNA tests only when there is a 'strong prima facie case' to ensure that the technology is not used to cause 'mental trauma' or social stigma to a child unnecessarily.

Sources: Indian Polity, M. Laxmikanth (7th ed.), Landmark Judgements and Their Impact, p.640; Geography of India, Majid Husain (9th ed.), Industries, p.62

6. Mechanism of DNA Fingerprinting (Profiling) (exam-level)

To understand DNA Fingerprinting (or profiling), we must first look at the biological 'why.' While 99.9% of human DNA is identical, the remaining 0.1% contains high levels of variation known as DNA Polymorphism. These variations occur primarily in non-coding regions (the 'junk' DNA) and accumulate over generations because they do not negatively affect survival Science , class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.119. In these regions, we find Variable Number Tandem Repeats (VNTRs) and Short Tandem Repeats (STRs) — sequences where a short chemical code repeats multiple times. The number of these repeats is unique to every individual (except identical twins), acting like a genetic barcode.

The modern mechanism of DNA profiling generally follows a sequence of sophisticated steps to turn a biological sample into a readable 'print':

• Extraction and Amplification: DNA is extracted from samples like hair, blood, or skin. Since the sample is often tiny, PCR (Polymerase Chain Reaction) is used to create millions of copies of the specific STR regions we want to study.
• Fragmentation: In older methods like RFLP, Restriction Enzymes (molecular scissors) cut the DNA at specific sites. Modern STR analysis focuses directly on the length of the repeated sequences.
• Electrophoresis: The DNA fragments are placed in a gel and subjected to an electric field. Because DNA is negatively charged, it moves toward the positive pole. Smaller, shorter fragments move faster and further than larger ones, separating the DNA into a distinct pattern of bands.
• Matching: The resulting pattern is compared. For paternity testing, every band in a child's profile must have a corresponding match in either the mother's or the biological father's profile.

This technology is not just for human forensics; it is a vital tool in biosurveillance and conservation. By building a 'library of life' and using DNA barcoding, scientists can identify species and track the health of ecosystems Environment, Shankar IAS Acedemy .(ed 10th), Conservation Efforts, p.249. Similarly, studying variations in mitochondrial DNA (mt-DNA) allows us to trace ancient human migrations back thousands of years History , class XI (Tamilnadu state board 2024 ed.), Early India, p.1.

Feature	STR Analysis (Modern)	RFLP (Traditional)
Sample Size	Requires very little DNA (due to PCR).	Requires large, high-quality samples.
Target	Short repeats (2-5 base pairs).	Longer variable repeats (VNTRs).
Speed	Rapid; automated.	Slow; manual and labor-intensive.

Sources: Science , class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.119; Environment, Shankar IAS Acedemy .(ed 10th), Conservation Efforts, p.249; History , class XI (Tamilnadu state board 2024 ed.), Early India: From the Beginnings to the Indus Civilisation, p.1

7. Solving the Original PYQ (exam-level)

Now that you have mastered the fundamentals of Mendelian inheritance and the unique structure of the human genome, this question asks you to apply those building blocks to a real-world forensic scenario. The core principle here is that a child inherits exactly 50% of their DNA from each biological parent. To establish paternity, a scientist must look for specific, unique genetic markers—essentially biological "barcodes"—that the child shares with the father but which are rare in the general population. This leap from general genetics to individual identification is what the UPSC is testing here.

To arrive at the correct answer, DNA finger-printing (Option D), you must identify the technique that focuses on individual variation rather than species-wide traits. As explained in Nature Scitable, DNA fingerprinting (or profiling) uses methods like STR (Short Tandem Repeat) analysis to compare specific loci across the genome. If the child possesses genetic fragments that are not present in the mother, they must have been inherited from the biological father. This method is the only one listed that provides the high statistical certainty (often >99.9%) required for legal and medical proof of paternity.

It is crucial to recognize why the other options are classic UPSC "distractors." Protein analysis (A) is far too generic, as many unrelated people share the same protein structures or blood types. Chromosome counting (B) is a trap designed to catch students who confuse "genetics" with "identity"; since almost every healthy human has 46 chromosomes, counting them tells you nothing about individual parentage. Finally, Quantitative analysis (C) merely measures the mass or volume of DNA present, which does not reveal the sequence or pattern needed to prove a biological link. Thus, DNA finger-printing remains the most scientifically robust and logical choice.