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
http://www.hshairclinic.co.uk/_images/hair_structure.jpg
Root
• When pulled from head, some translucent tissue surrounding the hair shaft near the root may be found
• Called “follicular tag”
http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/jan2004/research/images/fig58.jpg
Follicular Tags: Can be used for DNA analysis
http://hannahc12.files.wordpress.com/2010/04/picture-92.png
Hair Shaft Structure: Cuticle, Cortex and Medulla
• 3 sections to a hair shaft– Medulla (interior)– Cortex (main
section)– Cuticle (exterior)
http://3.bp.blogspot.com/_xvklWrDLexk/S8txNTzoVbI/AAAAAAAACAg/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
http://www.ecobyte.com.au/a_Basic_Hair_struc_Xsec.jpg
Hair Medulla
• Cellular column running through the center of the hair
• Can be continuous, interrupted or fragmented
http://intro.chem.okstate.edu/chemsource/Forensic/forechem11.gif
Hair Medulla
• Presence and appearance varies among individuals
• Most human hairs have no or fragmented medulla
• Asian hairs may have continuous medulla.
http://www.bfro.net/images/whatis/figures/Fig.%203%20with%20caption.jpg
Shape of the medulla
• Shape varies by species
• Humans: medulla is nearly cylindrical
• Animals:– Cat: bead-like – Deer: spherical cells
http://www.personal.psu.edu/users/c/l/clv14/sci101/images/standardhair%20copy.jpg
Medullary Index
• Varies by species• Calculation:
Width of Medulla = MIWidth 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
