Lecture 8: Trace Evidence

class characterisitics

associate an item to a particular class or group

Individual characteristics

can attribute to a source with high degree of certainty

trace evidence

small, sometimes microscopic material, which is transferred during commission of a crime 

cuticle of hair

scale structure covering the exterior of hair, formed by overlapping keratin cells that always point toward the tip end of each hair 

cortex

the main body of the hair shaft, comprised of spindle shaped cortical cells aligned in a regular array, parallel to the length of the hair 

medulla

a cellular column running through the center of the hair

what are the four classifications of the medulla?

continuous, interrupted, fragmented, and absent

root

the root and surrounding cells within the hair follicle assist with producing hair and hair growth 

anagen phase

the initial growth phase during which the hair follicle actively produces hair

catagen phase

a transition stage between the anagen and telogen phases of hair growth

telogen phase

the final growth phase in which the hair naturally falls out form the skin

anagen roots

soft and pliable, but will dry and harden when exposed to air

telogen roots

highly keratinized, distinct club-shaped root bulb, medulla will not extend into the root of the telogen phase

catagen roots

begun transition to keratinized bulb but remnants of rooth sheath typically present

tapered

newly formed hair has a natural taper to a fine tip

cut hair

well defined ends that could be squared or angled

rounded/abraded hair

smooth, convex tips due to gradual abrasion of cortical cells

frayed hair

appearance of a brush with cortical cells appearing as splayed fibrils

split ends

longitudinal splitting of hair

lanugo

fine, unpigmented, absent medulla, shed before or shortly after birth

vellus

fine, short, absent medulla, typically un-pigmented or light colored hair, present on almost all skin surfaces including forehead, nose, and ears

terminal hairs

typical hairs that are macroscopically visible

guard hairs (animal)

longer, stiffer hairs in the main coat

fur hairs (animal)

aka underhairs, fine hairs in the main coat that are devoid of microscopical characteristics useful for identification purposes

whiskers (animal)

long, stiff hairs that have often provide sensory function

head hairs

diameter varies but is uniform for given hair, length varies, narrow medulla if present, cut or frayed tips 

pubic

coarse and wiry, irregular cross sectional shapes and contours with twists, distinct buckles observed microscopically, moderate in length, thick medulla, telogen roots often possess follicular material 

axillary hairs

resembled pubic hairs but generally shorter and thinner without contour irregularities and distal tips may be abraded or frayed and appear lighter or yellowish in color 

what type of DNA testing is used when a follicular tag is present?

nuclear DNA

what type of testing is used when a follicular tag is not present?

mitochondrial DNA

natural fibers

derived from animal or plant sources, and animal fibers are most encountered in crime labs

manufactured fibers

derived from either natural or synthetic polymers, fibers are typically made by forcing the polymeric material through holes of spinneret