Chapter 8 Hairs & Fibers.

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Presentation transcript:

Chapter 8 Hairs & Fibers

Hair Appendage of the skin Grows from hair follicle Color & structure are important forensic features Composed of 3 layers

Hair Shaft Layers Cortex Cuticle Medulla

Cuticle Outside covering Made of scales Different species  different scale patterns

Cortex Main body of hair Contains pigments that give hair its color

Medulla Central canal Varies in thickness (by species) Not present in all hairs

Types of Medullas Continuous: Interrupted: Fragmented: Absent

Hair Growth Occurs at root Grows at a rate of 1 cm/month 3 phases: Anagen  Catagen  Telogen

Anagen Phase Initial growth (lasts 2 – 8 years) Follicle is actively making hair Root bulb  flame shaped **Follicular Tag  Clear tissue around hair (near root)  BEST source of DNA

Catagen Phase Growth slows Follicle breaks down Root bulb shrinks Lasts 2 – 4 weeks

Telogen Phase Resting phase Growth stops Hair falls out Root bulb  club shaped No more than 10% of follicles are in telogen at any time!!

Identification of Hair Determine whether it’s human or animal Scale Structure Medulla Shape Medullary Index **Problem  Hairs can vary from one to the next in the same individual** Help make an ID

Comparison of Hair View hairs with comparison microscope Need standard/reference samples to compare the evidence to  50 head  24 pubic Color, length, & diameter must match

Hair Evidence CAN Determine … Place of body origin  head, beard, pubic Race  but only sometimes Hair Evidence CANNOT Determine … Age or sex of an individual

Special Note Hair is an important piece of evidence, BUT is only 100% when DNA is analyzed!!!

Fibers Can be natural or man-made Important in homicides, assaults, & sexual offenses (Cross-transfer) BUT mass production of fabrics has  evidential value

Natural Fibers Come from animal or plant sources Wool  Sheep Cashmere  Goat Mink Cotton  Plant  Twisted, ribbon-like shape Animal

Cotton Wool

Flax Fibers Viewed with Polarized Light

Man-made Fibers Rayon (1911) Nylon (1939) Polyester Acrylics Spandex Synthetic

Rayon Nylon

Identification of Fibers Try to trace their origin Examine color & diameter with comparison microscope Look for striations & cross-sectional shape Determine dye composition

Cross-section of Man-made Fibers SEM Cross-section Cross-section of Man-made Fibers SEM Cross-section of Nylon Carpet Fibers

Collection & Preservation Remove fibers with clean forceps Package articles of clothing separately Use adhesive tape lifts on carpet, rugs, & bedding