Topic: How is hair studied by a forensic scientist?

Do Now: How often do you get your hair cut? How do people change the appearance of their hair?

HW: Textbook pg. 230 #’s 1-5

What is hair?

• Appendage of the skin

• Grows out of organ called the follicle

What are the parts of a hair strand?

• 1. Root/bulb• Embedded in hair follicle

• 2. Shaft• Composed of 3 layers

–Cuticle–Cortex–Medulla

• 3. Tip• Where the hair strand ends

Parts of the shaft• a. Cuticle

– Outside covering of hair– Made of hardened and flattened scales that overlap (like

shingles on roof)– Scales always point towards tip of hair– Useful for species identification– Can’t be used to individualize one human hair from others

Parts of the shaft• b. Cortex

– Made from spindle shaped cells– Arranged in pattern parallel to length of hair– Filled with pigment granules that give hair color– When we dye hair, we add pigments to cortex and

cuticle– When we bleach hair, we remove pigments

How can we tell the natural hair color of a person by looking at a hair sample?

• Hair grows about 1 cm per month• You can see difference in color if the

person hasn’t dyed/ bleached their hair for some time

Parts of the shaft• c. Medulla (plural is medullae)

– Cells form canal-like structure through hair– Medulla is very narrow in humans– More than half the width of animal hair is made up

of the medulla– Appearance/presence of medulla varies:

• From person to person • Among different hairs on the same person• From species to species

Medulla Shape• Medullae of animals tends to be in a pattern

UNISERIAL (rabbit)

MULTISERIAL (rabbit)

VACUOLATED (dog, fox, common)

LATTICE (deer)

AMORPHOUS (human,common)9

c. Medulla

• 3 types of medulla found in huma hairs– I.Continuous - most East Asian scalp hairs + pubic hair– II.Fragmented – – III.Absent-

Most human scalp hairs other than East Asian

Continuous Medulla

Solid canal throughout hair

Fragmented Medulla

Interrupted canals throughout hair

Absent Medulla

No Medulla Found

Parts of a hair strand

• 3. Root/Bulb– Helps make and grow hair along with

surrounding cells in follicle– When hair is pulled from root, a follicular tag

may be attached– We can get DNA from follicular tag

Can we determine where on body hair originated from?• Yes!• Scalp Hairs

– shows little diameter variation– Pigment is evenly distributed in cortex

• Pubic Hairs– Wide variation in diameter– Have continuous medullae

• Facial Hairs– Are coarse and triangular cross section

shape

• Hair analysis video