Download
1 / 18
180 likes | 355 Views
Forensic Hair Analysis. 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
E N D
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
Medulla Cont’d • Shapes and patterns • Cylindrical • Pearl • spherical
Root • Grows in 3 developmental phases: • Anagen • Catagen • Telogen
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 Types • Head • Pubic • Eybrow/Eyelash • Beard/Mustache • Body • Axillary hypertrichosis
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.
