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Trace Evidence: Hair
• Encountered at crime scenes
• Not good for “individualization” of physical evidence
1. No distinctive chemical properties
2. Although structural pattern exists, great amount of variation
• Hair provides corroborative evidence to place an individual at a crime scene
• DNA testing has linked a hair to an individual
*only if follicular tissue or root attached
*only if hair in particular growth phase
*analysis of mitochondrial DNA
• Combo of microscopic, genetic and ample control samples necessary-good? No, b/c can’t distinguish b/w mDNA and hair structure
Morphology of Hair
• Cuticle– Scale structure covering exterior of hair
– Seen with a “scale mount”
• Cortex– Main part of the hair shaft
– Most forensic evidence: pigment granules-size, arrangement, shape and color
• Medulla– Looks like a central canal if present; pattern continuous, interrupted,
fragmented
– “medullary index” = diameter of medulla relative to diameter of shaft expressed as a fraction
– Has shape which varies from species to species
Hair Growth
• Root –produces the hair
• Phases of Growth1. Anagen – initial growth; follicle actively producing hair; had follicular tag;
2. Catagen – transition stage; hair bulb shrinks in size
3. Telogen – final growth; hair falls out
Human Hair: Microscopic Features Caucasion Negroid Mongoloid
Shaft of Hair: extends from skin
Human Medulla Patterns
interrupted
absent continuous
Human Scale Pattern:Pattern of the cuticle
Human Feature For Comparison
• Body location
• Length of shaft
• Medullary index
• Diameter
• Presence of absence of medulla
• Distribution of shape and color intensity of pigment granules present in the cortex
• Artificial treatment –dye
• Tip and Base of Hair
Human vs. Animal
• Medullary index = less than 1/3
• Medulla has a shingle like appearance
• Large portion is cortex
• Medullary index = greater than ½
• Medullar has a patterned shape
• Small portion is cortex