Words to Know Cuticle Cortex Medulla Anagen phase Catagen phase Telogen phase Follicular tag Trichology Melanin granules.
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Words to Know Cuticle Cortex Medulla Anagen phase Catagen phase Telogen phase Follicular tag Trichology Melanin granules
Individualization of Hair
Unable to individualize a human hair to any single head or body through its Morphology Structural
characteristics
Link hair DNA to DNA of donor
Examination of Hair
1st step to examination of hair starts with color and structure or morphology.
The presence of hair at a crime scene denotes physical contact between a victim and assalent that is usually violent in nature.
Hair Morphology Hair: appendage of skin that grows
out of an organ known as the hair follicle.
Withstands chemical decomposition and retains structural features.
Length of hair extends from its root, continues into the shaft, and terminates at the tip end.
Shaft is composed of three (3) layers: Cuticle Cortex Medulla
Pencil analogy
Cuticle The scale structure covering
the exterior of the hair. Formed by overlapping scales
that always point toward the tip end of each hair.
Scales: hardened and flattened specialized cells (keratin) that progress form the follicle. Used in species identification
Must make a cast of scales and view under microscope for examination.
Cortex The main body of the hair shaft Housed within the cuticle Made of spindle-shaped cortical
cells aligned in a regular array, parallel to the length of the hair.
Where hair gets its color – pigmented granules The spacing and distribution of these
granules are an important characteristic when comparing two hairs.
Melanocytes: give color to hair. Examined microscopically using
liquid medium and reflected light.
Medulla
A cellular column running through the center of the hair.
Predominant feature in animals occupying more than half the hairs diameter.
Humans medulla usually occupies 1/3 of hairs diameter.
Medullary index: measures the diameter of the medulla relative to the diameter of the hair shaft. Normally expressed as a fraction. 0-1
Medulla Cont’d
Vary from individual to individual and even hair to hair or may not exist at all.
Classified three (3) ways: Continuous Interrupted Fragmented
Human hair are usually fragmented or medulla are absent. Exception Mongoloid Race (East Asian, North
Asian or Native American decent) have continuous medulla
Animal medulla either continuous or interrupted
Anagen (growth) Phase
Initial growth phase during which the hair follicle actively produces hair.
Growth may last up to 6 years Root has flame-shaped appearance. When pulled a follicular tag may be
present Translucent piece of tissue surrounding the
hair’s shaft near the root and contains the richest source of DNA associated with hair.
Important in individualizing hair.
Catagen (transition) Phase
A transition stage between the anagen and telogen phases of hair growth.
Last 2 – 3 weeks Root takes on an
elongated appearance.
Telogen (resting) Phase
Final growth phase in which hair naturally falls out of the skin.
Root takes on a club-shaped appearance.
After 2 to 6 months of hair growth, the hair will naturally shed.
Hair Identification and Comparison 1st must be determined as
human or animal Examine scale structure,
medullary index, and medullary shape for identification.
Hair comparison is collected from head and pubic area. 30-50 samples needed.
When comparing hair need to match:
color
Length Diameter Color intensity of granules in
cortex. presence/absence of medulla shape of medulla distribution of medulla
Collection and Preservation
Hair reference samples must come from the same area of the body as questioned samples Head hairs Pubic hairs
30 -50 full length hairs Use tweezers or forceps and should be stored
in bottles with snap-on lids. Rape cases; use clean comb on pubic area to
remove any foreign hair present before victim is sampled. Comb should then be packaged as evidence.
All microscopic hair comparisons must be confirmed by DNA analysis.
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