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Sherlock Holmes Forensic Series: DNA

During the era of Sherlock Holmes, fingerprinting was the most accurate way to place a suspect at the scene of a crime. The technique was revolutionary and helped put many criminals behind bars. Today, an even more accurate method of identification is used – DNA Profiling. Because they are highly accurate, DNA results are admissible in court as reliable evidence. Although 99.9% of human DNA sequences are the same in every person, the genetic material is different enough to distinguish one individual from another.

DNA is a chemical found in all the cells of our body – hair, blood, sperm, or even the skin on our hands or inside of our cheeks. In order to obtain cells, cotton tip swabs are used to collect blood, saliva, or other body fluids. Hairs can be collected with tweezers or tape. DNA profiling is accomplished in a laboratory by first extracting DNA from the nucleus of cells. Then the DNA is quantified to determine how much was obtained during the extraction step. After quantification, many copies of the DNA are made using a chemical process called polymerase chain reaction, or more commonly known as PCR. Finally, the copied DNA is analyzed on a genetic analyzer which provides the DNA profile. To determine whose DNA was profiled, forensic scientists search the national DNA databank. This databank, or CODIS which stands for Combined DNA Index System blends computer and DNA technologies into a tool for fighting crime.

CODIS uses two indices to generate investigative leads in crimes where biological evidence is recovered from a crime scene. The Convicted Offender Index contains DNA profiles of individuals convicted of felony sex offenses and other violent crimes. The Forensic Index contains DNA profiles compiled from crime scene evidence. CODIS utilizes computer software to automatically search its two indices for matching DNA profiles. Law enforcement agencies at federal, state and local levels take DNA from biological evidence gathered in crimes and compare it to the DNA profiles stored in the CODIS systems. If a match it made between a sample in a stored profile, CODIS can identify the perpetrator.

Sherlock Holmes used the best technology of his era to solve crimes. Like Holmes, modern day investigators observe and document, collect and preserve evidence. Today, DNA analysis provides investigators with a powerful tool beyond what Holmes could have imagined.

Sherlock Holmes Exhibit

The International Exhibition of Sherlock Holmes was developed by Exhibits Development Group and Geoffrey M. Curley + Associates in collaboration with the Conan Doyle Estate Limited, the Oregon Museum of Science and Industry, and the Museum of London.

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