Transcript Hair Evidence - Forensic Science

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-sciencecommunications/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
– Coronal
– Spinous
– Imbricate
Imbricate
Cuticle: scale structure
covering the exterior of hair
• Coronal: crown-like
pattern; like stacked
cups
Coronal
– Rodent
• Spinous: triangular,
petal-like scales
– Cat
Spinous
• Imbricate: flattened
scales with narrpw
margins
– Human
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%20capt
ion.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 = 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