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DNA fingerprinting is in your Class 12 biology book as a technique invented in Britain. India's version of the story starts somewhere unexpected: a PhD on the sex chromosomes of snakes. Lalji Singh followed a piece of basic research for more than a decade until it turned into a tool that police, courts and wildlife officers now rely on. Our post on DNA fingerprinting and the Human Genome Project for NEET covers the NCERT steps and the paternity questions. This post is about the scientist, and about the probability idea that makes a DNA match convincing.
Who was Lalji Singh?
An obituary in Current Science (2018) by his colleague K. Thangaraj gives the outline. Singh was born on 5 July 1947 in Kalwari village, Jaunpur district, Uttar Pradesh. He did his PhD at Banaras Hindu University on sex chromosomes in snakes, under S. P. Raychaudhuri. He then went to K. W. Jones's laboratory at the University of Edinburgh on a Commonwealth Fellowship and stayed from 1974 to 1987. Nature India reported that he died on 10 December 2017 in Varanasi, aged 70.
What was Bkm, and why did it matter?
At Edinburgh, Singh showed that female banded kraits, a highly venomous snake, carry large amounts of a sex-chromosome-associated satellite DNA, later called Bkm (banded krait minor satellite). The papers he wrote with Ian Purdom and Kenneth Jones, such as Sex chromosome associated satellite DNA: evolution and conservation (1980) in Chromosoma, followed it across species. Thangaraj notes that Singh showed the sequence is found in all vertebrates, including humans.
That last finding is what connected snakes to forensics. Satellite DNA is made of short sequences repeated many times, and the number and position of repeats varies from person to person. A probe that sticks to such repeats lights up many places in a person's DNA at once, which is what "multilocus" means.
How did it become India's DNA fingerprinting probe?
Singh returned to India in 1987 at the invitation of P. M. Bhargava, founding director of the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad. According to Thangaraj, his Bkm work there led to the first indigenously developed multilocus probe for DNA fingerprinting, made almost at the same time as the first probe developed abroad, and India became only the third country, after the UK and USA, with the technology.
Singh did not stop at the laboratory. He took the method to investigators and appeared in court himself. In 1991 a Sessions Court in Tellicherry, Kerala, accepted his DNA fingerprinting evidence, which Thangaraj describes as a first for the Indian judiciary. He founded the Association for Promotion of DNA Fingerprinting and Other DNA Technologies in 1993, and proposed and set up the Centre for DNA Fingerprinting and Diagnostics (CDFD) in Hyderabad, serving as its first officer in charge from October 1995 to February 1999. He became director of CCMB in 1998, set up its Laboratory for the Conservation of Endangered Species (LaCONES), received the Padma Shri in 2004 and was Vice-Chancellor of BHU from 2011 to 2014.
Worked example: why a multi-band match is convincing
This example uses made-up numbers to show the logic; real forensic statistics are more careful. Suppose a multilocus probe shows 10 bands for a suspect, and suppose any one of those bands turns up in an unrelated person with probability 0.25.
Chance an unrelated person shares 1 given band: 0.25
Chance they share all 10, if the bands are independent: 0.25¹⁰
0.25¹⁰ = (1/4)¹⁰ = 1 ÷ 1,048,576, about 1 in a million
Each extra band multiplies the probability by another 0.25. With 15 bands it would be 1 in about a billion (4¹⁵ = 1,073,741,824). That is why many bands from one probe make a strong fingerprint.
Common mistakes:
Assuming bands are always independent. If two bands tend to be inherited together, multiplying overstates the rarity.
Forgetting relatives. Close relatives share far more bands than strangers, so the "unrelated person" figure does not apply to a brother or cousin.
Reading "1 in a million" as "a 1 in a million chance the suspect is innocent". It is the chance that a random unrelated person would match, which is a different question.
What else came out of the same idea?
Thangaraj describes a "universal probe" for wildlife forensics developed by Singh and a colleague, which can tell from a drop of blood, a hair or a piece of meat whether it came from a human or an animal and, if an animal, which species. It has helped in hundreds of wildlife crime cases and even in identifying birds in aircraft bird strikes. Singh's team also studied Indian populations, including work on the Andaman islanders published in Science.
What can a student take from Lalji Singh?
Three habits stand out in his career. He stayed with one research question long enough to understand it deeply. He was willing to carry a result out of the lab, into courtrooms and policy, which took a different kind of effort. And he built institutions, CDFD and LaCONES among them, so the work would continue without him. If you are thinking about a career in biology, his path shows how far a question about snake chromosomes can travel.
If the link between repeated DNA and a banding pattern is still hazy, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can revisit satellite DNA and electrophoresis before tackling exam questions.
Try it now: redo the worked example with a band frequency of 0.2 and 12 bands, and write the answer as "1 in" a round number.
