anatomy of hair - wordpress.com...animal vs human hair the medulla is a string of dots in animal...

Forensic Value of Hair

Hair is class evidence – morphorlogy

(how it looks), index (how thick the

medula is), color

Mitochondrial DNA from shaft. All

mitochondria comes from egg only, not

sperm. So ONLY maternal lineage

If hair bulb (root) is present, then can get

nuclear (individual DNA) from it

Hair is Class evidence ONLY

A piece of hair cannot be individualized to a particular head/person Rather it can be characterized and classified

Comparative Microscope Allows technician to compare two hairs side by

side Comparison Microscope Two matching hairs

When is hair evidence

important in a case?

Animal or Human determination

Body area determination

Race association with hair

Animal vs Human Hair

The medulla is a string of dots in animal hair.

humans frequently lack medulla

Pigment in animal hair tend to clump, human

hair pigments more evenly distributed

Animal hair has distinct banding

Human hair color is constant throughout

MOST IMPORTANT – animal medulla is

pretty thick, while in humans the medulla is

thin or lacking

The Medulla Index is the ratio of the medulla width to

the entire hair width. It is much bigger in animals

than in humans

Human hair

Dog hair

Animals have a more patterned

medulla than humans

HUMAN HAIR

• The root is club-shaped

• Consistent in color and

pigmentation throughout

the length of the hair

• Medullary index is less

than 1/3

• Pigment is evenly

distributed, slightly more

dense near the cuticle

Pigment Distribution in Human

Hair • Pigment granules are small,

dark, and solid structures

• They vary in color, size, and

distribution in a single hair.

• In humans, pigment granules

are commonly distributed

toward the outer edge of cortex

• The exception is red-haired

individuals, granules are

concentrated along the center of

the hair

Brown Human Hair

Red Human Hair

Ovoid bodies found in Dog

Hair

Ovoid bodies are abundant

in Cattle hair

The cuticle scales are very

distinct from species to species

A species is defined as organisms that can

interbreed and produce fertile offspring

Rabbit – Spinous cuticle

pattern

Can you identify the animal hairs shown?

Think About It …

(1) In which samples are we viewing the cuticle? How do they compare?

(2) In which samples are we viewing the medulla? How do they compare?

(3) What characteristics can be used to identify hair samples?

Types of Animal Hairs - Key

A B C D

E F

G

I H

Cat Horse Pig Human

Deer Dog Rat Rabbit Human

Hairs might show signs of

cutting

Which hair was cut by a razor?

Which was cut with scissors?

Which split on its own?

Pubic Hairs

One of the kinds of evidence where the mere

presence will suggest foul play.

Pubic Hairs

Coarse, Wiry

Diameter’s show a lot of

variation

Buckling and tapered ends

are common

Racial Type of Hair

Compare these cross-sections of three hairs, all of different racial types:

(left) Asian, (center) Caucasoid, (right) African

African-Origin Hair

• Shaft diameter: moderate

to fine with considerable

variation

• Pigment granules: densely

distributed (hair shaft may

be opaque) and arranged

in prominent clumps

• Shaft: prominent twist and

curl

Asian-Origin Hair

• Shaft diameter: coarse and

usually with little or no

variation

• Pigment granules: densely

distributed and often

arranged in large patchy

areas or streaks

• Medulla: prominent (often

broad and continuous)

• Cuticle: thick

Caucasian-Origin Hair

• Shaft diameter: moderate with

minimal variation (mean

diameter for human head hairs -

80um)

• Pigment granules: sparse to

moderately dense with fairly

even distribution

Epidermis - protects skin, renewed

frequently

Sebaceous gland, sebum, lubricates and

waterproofs skin and hair, mostly on face

and scalp, not palms or soles

All the blood supply to the hair comes

from the bottom portion of the hair in the

dermis.