Q.'There is a paternity dispute for a child'. Which technique can solve the problem. Discuss the principle involved.
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Start your 14-day free trial to unlock the full solution →DNA fingerprinting can resolve paternity disputes by comparing the unique genetic profiles of the child, mother, and alleged father — a child inherits exactly half its DNA bands from each biological parent.
When a paternity dispute arises, the question at stake is biological: did this man contribute half of the child's genetic material? The answer lies in a technique called DNA fingerprinting, also known as DNA profiling or genetic fingerprinting. Developed by Alec Jeffreys in 1984, this method revolutionized forensic science and became the gold standard for establishing biological relationships.
DNA fingerprinting works because every individual (except identical twins) carries a unique pattern of DNA sequences. While most of our DNA is identical across humans, certain regions contain highly variable repetitive sequences called VNTRs — Variable Number Tandem Repeats. These are short DNA sequences repeated multiple times in tandem, and the number of repeats varies enormously from person to person. Some people might have a sequence repeated 10 times at a particular location, others 25 times, and so on. These differences create a distinctive genetic "barcode" for each individual.
The technique involves several steps. DNA is first extracted from samples — typically blood, hair roots, or cells from a cheek swab — from the child, the mother, and the alleged father. The DNA is then cut into fragments using restriction enzymes, which act like molecular scissors that recognize and cut at specific sequences. These fragments are separated by size using gel electrophoresis, where smaller fragments travel farther through the gel than larger ones. The separated fragments are transferred to a nylon membrane and treated with radioactive probes that bind specifically to the VNTR regions. When exposed to X-ray film, the result is a pattern of dark bands — the DNA fingerprint.
The principle of inheritance is central: a child receives exactly 50% of its DNA from the biological mother and 50% from the biological father. Therefore, every band in the child's DNA fingerprint must match either a band from the mother or a band from the father.
In a paternity test, the examiner compares the three profiles side by side. First, the bands that match the mother are identified — these account for half the child's bands. The remaining bands must have come from the biological father. If the alleged father's profile contains all these unmatched bands, paternity is established with extremely high probability (typically over 99.9%). If several bands in the child's profile have no match in either the mother's or the alleged father's profile, he is excluded as the biological father. …
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