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An Explorit "Science Bytes" article by Jennifer LeBlanc (1996)

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by Jennifer LeBlanc (1996)

"It is elementary, my dear Watson," Sherlock Holmes would say to his plodding assistant as he announced the solution to a mysterious crime. Created by Sir Arthur Conan Doyle in 1886, Sherlock was - and remains - the master of the art of deductive reasoning. Based on his careful observations, Sherlock solved mysteries that stumped the other characters and usually the reader.

Modern police detectives can find clues in ways that would have baffled even Sherlock Holmes. For example, when a fire scene is analyzed, it is now possible to detect such details as where the blaze began and who or what started it. Such deductions may seem incredible but they are based on the careful work of forensic scientists.

Forensic science is defined by The Concise Oxford Dictionary as science that is " . . . used in courts of law." It encompasses many scientific disciplines, such as anthropology, ballistics, chemistry, graphology, medicine, toxicology, and psychiatry. However, the term generally invokes television images of murder cases, coroner reports, and other medical evidence.

Murder is a bloody crime. Detectives have been using serology, the study of blood fluids, to track criminals for over a hundred years. Serology tests can determine whether the fluid at a crime scene is indeed blood, whether it is of animal or human origin, and can sometimes provide physical and biological clues about the criminal.

Early in the 1900s, the first system to classify blood types was developed. We now know these blood types as A, B, AB, and O. There are several other systems of classifying blood samples, which also were developed in the first half of this century. These blood grouping systems can help police if, for example, a rare blood type is found at a crime scene and the suspect shares that blood type. There are also distinct variations in the shape of red blood cells and other blood components that can help link a killer to the crime. Sometimes, this evidence is enough to force a confession or secure a conviction. Only a small sample of blood is needed and many of these tests can even be done on dried blood stains.

In 1984, a serendipitous breakthrough caused a revolution in serology and forensic science. Dr. Alec Jeffreys from Leicester University (U.K.), while working on another problem involving DNA (deoxyribonucleic acid), discovered the technique for genetic fingerprinting. He found that although most of the genetic code within DNA molecules is the same in all humans, there are small sections, called hypervariable regions, that are uniquely coded in every individual. To find these unique sections, he developed a set of DNA probes, which are short pieces of radioactively-labeled DNA. These probes, when added to a DNA sample, will bind in a unique pattern. This pattern, which is captured on radiosensitive film, is known as a genetic fingerprint.

Dr. Jeffreys, in a letter to Brian Marriner, author of On Death's Bloody Trail: Murder and the Art of Forensic Science, wrote " . . . on good-quality probes, we estimate the chance that two unrelated people have the same pattern at less than 1 part in 1,000,000,000,000,000,000, 000,000,000,000." Genetic fingerprinting can even be done on hair, semen or other body fluids. Since its discovery, this advanced serological technique has played an important role in many cases in Europe and North America and will continue to be an essential tool for detectives.

Sherlock Holmes and his creator, Sir Arthur Conan Doyle, surely would have thought the techniques of forensic science, especially genetic fingerprinting, were powerful methods for catching criminals. Please join us at Explorit during the Solving Mysteries with Science exhibit (January 20 - March 3, 1996). We will show you how to become a detective and use scientific techniques to solve everyday mysteries of your own.




  1. Doyle, Sir Arthur Conan Doyle. 1994. Adventures of Sherlock Holmes. New York, NY: Quality paperback Book Club. 
  2. Golob, Richard and Eric Brus, eds. 1990. DNA Probes. The Almanac of Science and Technology: What's New and What's Known. Boston, MA: Harvest/HBJ, pp. 110-112. 
  3. Jones, Steve. 1993. The Language of Genes: Solving the Mysteries of Our Genetic Past, Present and Future. New York, NY: Anchor/Doubleday. 
  4. Mariner, Brian. 1991. On Death's Bloody Trail: Murder and the Art of Forensic Science. New York: St. Martin's Press.


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