Hair Evidence. Hairs as physical evidence Valuable because can remain intact for years So strong that they have same tensile strength of steel of same.

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Presentation transcript:

Hair Evidence

Hairs as physical evidence Valuable because can remain intact for years So strong that they have same tensile strength of steel of same gauge Presence often denotes physical contact

Morphology (Structure) of Hair Made of keratin -- a protein Consists of: –Root (bulb) –Shaft –Tip

Root When pulled from head, some translucent tissue surrounding the hair shaft near the root may be found Called “follicular tag” communications/fsc/jan2004/research/images/fig58.jpg

Follicular Tags: Can be used for DNA analysis

Hair Shaft Structure: Cuticle, Cortex and Medulla 3 sections to a hair shaft –Medulla (interior) –Cortex (main section) –Cuticle (exterior) Kbk03aJ5u64/s320/hair-cross-section.gif

Cuticle: scale structure covering the exterior of hair Formed from overlapping scales that always point towards the tip end Useful in species identification 3 basic patterns: –Coronal –Spinous –Imbricate Coronal Spinous Imbricate

Cuticle: scale structure covering the exterior of hair Coronal: crown-like pattern; like stacked cups –Rodent Spinous: triangular, petal-like scales –Cat Imbricate: flattened scales with narrpw margins –Human Coronal Spinous Imbricate

Hair Cortex Main body of hair shaft Embedded with pigment granules that give hair color Can be used to compare hairs of different persons

Hair Medulla Cellular column running through the center of the hair Can be continuous, interrupted or fragmented

Hair Medulla Presence and appearance varies among individuals Most human hairs have no or fragmented medulla Asian hairs may have continuous medulla. ion.jpg

Shape of the medulla Shape varies by species Humans: medulla is nearly cylindrical Animals: –Cat: bead-like –Deer: spherical cells

Medullary Index Varies by species Calculation: Width of Medulla = MI Width of Cortex

Hair Comparison Matching color, length and diameter Can use microscope to distinguish animal hair from human hair Animals: distinguish using scale structure, medullary index and shape Humans: –distinguish by looking at presence or absence of medulla. –Distribution, shape and color intensity of pigment granules in cortex

Hair and DNA Mitochondrial DNA can be extracted from the hair shaft –Inherited only from mother The root contains nuclear DNA –Only present if hair is forcibly removed