DNA recognition instruments
DNA recognition instruments are essential tools used by crime scene investigators to detect biological materials from which DNA can be isolated for analysis. These instruments play a critical role in modern criminal investigations by helping to establish the presence of biological evidence, such as blood, saliva, or hair, which can be pivotal in proving the guilt or innocence of a suspect. Traditionally, locating such evidence relied on thorough physical searches; however, advancements in technology have led to the development of specialized light sources and chemical tests that enhance detection efficiency.
One of the primary tools in this area is the alternate light source (ALS), which includes ultraviolet (UV) lights that emit specific wavelengths to make certain biological materials fluoresce, aiding in their identification. In addition to UV lights, other ALS instruments, such as lasers, are gaining traction because they can target specific wavelengths without damaging DNA. Once a potential biological sample is identified, investigators typically conduct colorimetric tests to confirm its presence, using chemicals that react and change color in the presence of specific compounds.
Furthermore, commercially available detection kits assist forensic teams by enabling the identification of particular proteins or DNA types, including those that can differentiate between male and female DNA, a crucial feature in sexual assault investigations. Overall, DNA recognition instruments significantly streamline the process of gathering evidence at crime scenes, enhancing the overall efficacy of forensic investigations.
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DNA recognition instruments
DEFINITION: Instruments used by crime scene investigators to detect the presence of biological materials from which DNA may be isolated for analysis.
SIGNIFICANCE: The use of biological evidence, specifically DNA, to prove the guilt or innocence of suspects is an important component in modern criminal investigations. By using DNA recognition instruments at crime scenes to identify the presence of materials from which DNA evidence may be isolated—such as hair, saliva, or semen from suspects or victims—investigators increase the efficiency of evidence gathering.
The detection of (deoxyribonucleic acid) at a crime scene begins with the identification and isolation of biological such as blood, semen, saliva, or hair. Historically, such evidence has been found through physical searches of crime scenes, but the search process has been expedited by the development of specialized light sources and chemical tests.
Most commonly, the detection of biological samples has been aided by the use of ultraviolet (UV) light sources. UV lights belong to a class of instruments known as alternate light source (ALS) instruments. Unlike light sources that emit wavelengths of light across a broad spectrum, ALS lights use filters or special bulbs to emit a much narrower range of wavelengths. For example, UV lights emit wavelengths in the 400-200 nanometer range. The most common UV light is called a “black light,” which emits wavelengths in the 400-320 nanometer range, also known as UVA. These wavelengths are invisible to the human eye but may cause certain chemicals, mainly proteins, to fluoresce. UV lights are useful in the detection of blood, semen, and saliva. Other ALS instruments include copper and argon lasers and modified arc lamps. The use of lasers in DNA detection is becoming increasingly popular because lasers do not damage DNA strands and can emit very specific wavelengths of light.
ALS instruments can indicate fluorescing molecules, but upon finding such samples, investigators must confirm the presence of specific forms of biological evidence by using certain chemicals to perform presumptive tests. These are usually colorimetric tests, meaning that the reagents used in the tests change colors when exposed to specific compounds. For example, the for semen is specific for acid phosphatase, an enzyme that is more abundant in semen than in other body fluids. The presumptive tests for blood use human-specific antibodies that allow investigators to distinguish between human blood sources and the blood of other animals.
In addition to light sources and chemical tests, several commercially produced detection kits are available to forensic investigators. Among these are kits that can detect the proteins present in semen and kits that can detect the presence of DNA. Kits are also available that can disregard female DNA and indicate the presence of male DNA only, making them especially useful in and sexual assault cases.
Bibliography
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Butler, John M. Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers. 2d ed. Burlington, Mass.: Elsevier Academic Press, 2005
James, Stuart H., and Jon J. Nordby, eds. Forensic Science: An Introduction to Scientific and Investigative Techniques. 2d ed. Boca Raton, Fla.: CRC Press, 2005.
Sharman, Sarah. "Forensics and DNA: How Genetics Can Help Solve Crimes." Hudson Alpha, 11 Nov. 2021, www.hudsonalpha.org/forensics-and-dna-how-genetics-can-help-solve-crimes/. Accessed 14 Aug. 2024.