Trace Evidence Unit: Hair Analysis - Forensic Science

when a forensic scientist receives hair and/or fiber evidence from a crime scene, what must they determine? (4 questions)

1. is it a hair or is it a fiber?

2. if a hair, is it animal or human?

3. if animal, what species?

4. if human, whose hair is it?

what two parts do hairs consist of?

follicle and shaft

network of blood vessels that supply nutrients to feed the hair and helps it grow at the end of the follicle

papilla

bulb that contains a sebaceous gland secretes _____

oil

what is the name of the protein found in hair?

keratin

what does keratin do?

makes the hair strong and flexible

what are the three layers of the hair shaft?

cuticle, cortex, medulla

• transparent outer layer

• protects the hair

• scales overlap one another and point toward the tip end

cuticle

how can forensic scientists study the scale pattern of hair?

make a cast

how do you make a hair cast?

embed hair in a soft medium, such as clear nail polish; when medium has hardened, remove hair—this leaves a clear, distinct impression of the hairs’ cuticle

• middle layer

• largest part of the hair shaft

• contains pigment (melanin) granules

cortex

what are the two main pigments found in human hair?

eumelanin and phaeomelanin

eumelanin pigment

brown/black hair

phaeomelanin

blonde/red hair

• central core of the hair

• it can be a hollow tube or filled with cells

medulla

5 different groups of medulla

continuous, interrupted (intermittent), fragmented or segmented, solid, none

continuous medulla

one unbroken line of color

interrupted (intermittent) medulla

pigmented line broken at regular intervals

fragmented or segmented medulla

pigmented line unevenly spaced

solid medulla

pigmented area filling both the medulla and the cortex

no medulla

no separate pigmentation in the medulla

medulla structures

uniserial, multiserial, vacuolated, lattice, amorphous

uniserial animals

cat, rat

multiserial animals

rabbit

vacuolated animals

dog, fox

lattice animals

deer

amorphous animals

human

medullary index calculation

diameter of medulla/diameter of hair

medullary index <1/3

humans

medullary index >1/2

animals

3 phases of hair growth

anagen, catagen, telogen

• active growing phase

• follicle produces new cells, cells are dividing

• cells produce melanin or pigment

• lasts approximately 1 000 days

• 85% of all human hair

• can have a follicular tag

anagen

follicular tag

individual characteristic; a translucent piece of tissue surrounding the hair’s shaft near the root (best source of DNA in the hair)

• transition to resting stage

• follicle begins to shut down cell production cells shrink

• 2-3 weeks

• 2% of all human hair

catagen

• resting phase

• no cell production

• hair naturally falls out

• over 2-6 months

• 12% of all human hairs

telogen

how many samples of hair are needed to compare question vs. known hairs

50-100 hairs

what does a forensic scientist match when comparing hair?

color, length, diameter, presence/absence of medulla, distribution, shape, and color intensity of pigment granules, dyed or bleached hair from natural hair, damage, “critters'“

six types of hair on the human body

head hair, eyebrows and eyelashes, beard and mustache hair, underarm hair, auxiliary or body hair, public hair

what cross sectional shape do beard and mustache hair have?

triangular cross section

do hairs possess a sufficient number of unique individual microscopic characteristics to be positively identified as having originated from a particular person to the exclusion of all others?

no

microscopic consistency is ________

presumptive

presumptive definition

presumed in the absence of further information

DNA is __________

confirmatory (individual)

oblique lighting

using a light source at a low angle, usually to show detail by creating shadows in the subject surface

how can you collect hairs?

tweezers, specialized vacuum cleaner, scraping, combing, tape lifting, gel lifters, post-its

how can you package hair? (trace evidence)

druggist’s fold