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