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Hair Assay in Forensic Science

Hairs are slender fibrous outgrowths projecting from the pare that possess dissimilar microscopic characteristics such equally shape, colour, and root appearance. Variability in such features can help forensic scientists to determine age, gender, and racial origin of the person that shed the hair, as well as allowing i to determine which area of the trunk hair has come from. Hair can likewise be used to extract DNA for analyses that tin can assistance to narrow downwardly who may have been involved in a crime.

Human hair under microscope illustration. Image Credit: Kateryna Kon / Shutterstock

Hair Prove

Humans shed an average of approximately 100 head hairs per mean solar day, and considering pilus can exist easily transferred during physical contact information technology is commonly submitted as forensic testify to assistance plant associations between people (e.k. a victim and suspect) and/or people and a crime scene.

Such associative bear witness is especially useful in violent crimes where physical contact is likely to take occurred such as sexual attack, homicide, and aggravated assault. Crimes less likely to have involved physical contact such as armed robbery would typically involve collecting clothing or other items that may have picked upwardly hair that could be used to identify suspects.

Test of hair by microscopy can assistance to establish whether a hair was forcibly removed, diseased or treated with an artificial substance such every bit a hair dye. Forensic analysts utilise an instrument called a comparison microscope to view a known hair sample and an unknown sample aslope ane some other to see if they share similar characteristics and could accept come up from the same source.

Hair Comparison Microscopy

A comparison microscope, which is made upward of two chemical compound light microscopes connected past an optical bridge, allows the user to view a known and unknown hair sample simultaneously. The multi-stage examination procedure starts with the analyst establishing whether the unknown hair is of animal or human origin.

If information technology is an animate being hair, the examiner can further identify it as belonging to a particular species, although it cannot exist linked to a item animate being at the exclusion of other animals within the same species. Animal hairs plant on items of testify can link a suspect to a crime scene or a vehicle or location where a victim was held. Hairs from a pet the suspect owns, for example, may also exist transferred to the victim when a doubtable makes concrete contact.

If the hair is human being in origin, analysis can help to distinguish between individuals based on the arrangement, advent and distribution of certain characteristics inside different regions of the hair.

Factors to Consider

Many factors touch on the robustness of hair association analyses, including variations in the adequacy of equipment and staff feel and training.

Although hair microscopy is a valuable tool to utilise for identification purposes, accurately determining a statistical probability of a given clan is challenging, partly due to the lack of reliable quantitative assessment of hair characteristics.

However, the analysis tin allow i of the post-obit conclusions to be drawn:

Whether the unknown pilus exhibits like characteristics to the known hair and could therefore have originated from the same source every bit the known pilus
Whether the unknown pilus is dissimilar to the known hair and could not have originated from the same source
Whether both similarities and dissimilarities were seen between the two hairs, pregnant no decision about possible source of origin tin be fabricated

When forensic experts do observe shared characteristics between the known and unknown pilus, a statement such as the post-obit may exist added to their report:

"Pilus comparisons are not a basis for absolute personal identification. Information technology should be noted, however, that because it is unusual to find hairs from 2 different individuals that exhibit the same microscopic characteristics, a microscopic clan or match is the footing for a potent association."

In 2009, the National Academy of Sciences released a report called "Strengthening Forensic Science in the U.s.: A Path Forrad," which stated that since the advancement of Dna analysis, microscopic pilus assay should be bars to establishing which hairs to exam, and whether hairs share similar characteristics, simply should not exist considered a reliable tool for the identification of individuals suspects.

The Suitability of Hair for Dna Analysis

To test the suitability of a man hair sample for nuclear DNA analysis, hair microscopy is used to view the end of a hair and establish whether it contains a root. If so, the sample tin can be tested using a nuclear Deoxyribonucleic acid testing procedure called Curt Tandem Repeat (STR) assay. A hair that has been shed without a root cannot be sent for this type of testing, simply can still exist subjected to mitochondrial DNA (mtDNA) testing of the hair shaft.

A combination of microscopic hair comparisons and DNA analysis tin can provide a complementary approach that offers superior information about hair origin, compared with that obtained using microscopic pilus comparisons alone.

Under The Microscope: The FBI Hair Cases | Fault Lines

Farther Reading

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Chromatography in Forensic Science
Overcoming Deoxyribonucleic acid Degradation in Forensic Science
Reducing PCR Inhibition in Forensic Science

Last Updated: May 21, 2019

Written by

Emerge Robertson

Sally showtime developed an interest in medical communications when she took on the role of Journal Development Editor for BioMed Primal (BMC), later having graduated with a caste in biomedical science from Greenwich University.

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APA

Robertson, Sally. (2019, May 21). Pilus Assay in Forensic Science. News-Medical. Retrieved on June 13, 2022 from https://world wide web.news-medical.internet/life-sciences/Hair-Analysis-in-Forensic-Science.aspx.
MLA

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Chicago

Robertson, Emerge. "Pilus Analysis in Forensic Science". News-Medical. https://www.news-medical.cyberspace/life-sciences/Pilus-Analysis-in-Forensic-Science.aspx. (accessed June 13, 2022).
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Robertson, Emerge. 2019. Hair Analysis in Forensic Science. News-Medical, viewed thirteen June 2022, https://www.news-medical.net/life-sciences/Pilus-Analysis-in-Forensic-Science.aspx.