hair and fiber analysis
DESCRIPTION
Hair and Fiber Analysis. Morphology of Hair. Part of Integumentary System Grows out of hair follicle Hair consists of Root/bulb Shaft Tip end. Morphology Cont. Hair Shaft is the focus of most forensic analysis 3 Parts Cuticle-the scale structure covering exterior of the hair - PowerPoint PPT PresentationTRANSCRIPT
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Hair and Fiber Analysis
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Morphology of Hair
• Part of Integumentary System• Grows out of hair follicle• Hair consists of– Root/bulb– Shaft– Tip end
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Morphology Cont.
• Hair Shaft is the focus of most forensic analysis• 3 Parts– Cuticle-the scale structure covering exterior of the
hair– Cortex-the main body of the hair shaft– Medulla-a cellular column running through the
center of the hair
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The Cuticle in Detail
• Resistance to decomposition and retainment of structural features are due to cuticle
• Overlapping scales made of hardened cells• Scale pattern not useful in distinguishing
humans but can be utilized for species identification
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The Cortex in Detail
• Main body of the hair shaft made of cortical cells
• Embedded with pigment granules that give color to hair
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The Medulla in Detail
• Central canal of the hair• Medullary index- measures the diameter of
the medulla compared to diameter of hair shaft– Written as a fraction….humans less 1/3 animals ½
or greater• Medulla can be continuous, fragmented,
interrupted, or non exsistent
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The Root in Detail
• Allows for hair growth (three phases)– 1. Anagen phase- initial growth phase during which
the hair follicle actively produces hair– 2. Catagen phase- a transition stage between the
anagen and telogen phases– 3. Telogen phase- the final growth phase in which hair
naturally falls out of the skin• Follicular tag is the most important part because it
contains the “richest” source of DNA for the hair
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Misconceptions of Hair
• Hair CANNOT be used to identify a single head or body through its structural characteristics
• Only if DNA is present can it be matched• Can determine the area of the body that the
hair came from• Some racial origins can be determined from hair• Age and sex cannot be determined (exception
infant hair or dye)
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Fiber History
• Most fibers originally came from natural resources: plants and animals
• Post 1920 scientist created dozens of new fibers
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Types of Fibers
• Natural Fibers—animal or plant sources– Sheep—wool– Goats—mohair, cashmere– Camels, Llamas, Alpacas, mink, rabbit, beaver, and
muskrat– Cotton
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Types of Fibers
• Manufactured Fibers—fibers derived from either synthetic or natural polymers
• First of these were made from materials derived from cotton or wood pulp– Pure cellulose is extracted from them– Also called regenerated fibers
• Rayon, acetate, tracetate (all come from cellulose)
• Currently many are made solely from chemicals and are called synthetic fibers
• Nylons, polyesters, acrylics
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Rayon
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Natural and Synthetic Manufactured
• Cellulose—natural carbohydrate polymer• Synthetics– polymers are the basic unit of
these fibers
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Identification and Comparison of Manufactured Fibers
• Origin of the fiber is key in utilizing it as a piece of evidence
• First step is a microscopic examination– Look at the color, diameter, and longitudinal
striations– Cross sections of the fibers can also be beneficial
to tying fiber back to the manufacturer
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Cross Section
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Identification and Comparison of Manufactured Fibers
• Microspectrophotometer- compare colors of fibers through spectral patterns
• Chromatographic- analyze the dye composition by extracting dye from fibers themselves
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Identification and Comparison of Manufactured Fibers
• Fibers need to have the same chemical composition– Nylon and subgroups of nylon– Acrylic fibers can be broken down into 24 different
groups
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Identification and Comparison of Manufactured Fibers
• Birefringence-- polarize white light passing though a synthetic fiber is split into two rays that are perpendicular to each other
• Infrared Absorption– polymers that make up fiber selectively absorb infrared light in a characteristic pattern
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Collection and Preservation of Fiber Evidence