11/25/13
Learning Goal: Understand and apply concepts in
molecular biology
Warm-Up: A forensic scientist has collected hair
samples from a crime scene. Predict how you
believe they determine similarities and differences
in the samples.
Hair Evidence
Molecular Biology Techniques
The Function and
Structure of Hair
• Hair on mammals helps to regulate body
temperature, decrease friction, and protect
against sunlight.
• Hair consists of (a) a hair shaft produced by (b) a
follicle embedded in the skin.
• A hair has three layers (illustrated above): the
inner medulla, the cortex, and the outer cuticle.
Anatomy of a Hair
Hair Shaft
Sebaceous
gland
Epidermis
Dermis
Papilla
Follicle
•Hair is an appendage of the
skin that grows out of a
hair follicle.
Root
•The length of a hair extends
from the root embedded in
the follicle.
• A single root
contains
sufficient DNA
for analysis
Cuticle
•The cuticle is the transparent
outside covering of the hair.
•It is formed by overlapping
scales that always point
toward the tip of the hair.
Cortex
•The Cortex is the thickest layer
•It is the interior of the hair
•It is embedded with pigment
granules that give hair its color.
Pigment granules are absent in grey hairs
Medulla
•a collection of cells which
appears as a canal running
through the center of the hair
•the medulla is the most
predominant hair feature in
many species
Medulla:
bsapp.com
Forensic Science: Fundamentals
& Investigations, Chapter 3
12
Types of
Medulla
The medulla can be hollow or filled,
absent, fragmented, continuous,
doubled, pigmented, or un- pigmented.
Type of Medulla?
Types of Hair
Buckled
Blunt
Double Medulla
• Different regions of the body on which hair can
vary are (1) head, (2) eyebrows and lashes, (3)
mustache and beard, (4) underarms, (5) overall
body (auxiliary hair), and (6) pubic.
• The physical characteristics of hairs provide
information about which part of the body they
came from.
The Life Cycle of Hair
• Hair proceeds through 3 stages as it
develops:
• Anagen stage - hair actively grows. The
cells around the follicle deposit materials
in the hair.
• Catagen stage - hair grows and changes.
• Telogen stage - when the follicle becomes
dormant, hairs easily lost.
Treated Hair
• Bleaching disturbs the scales on the
cuticle and removes pigment leaving
hair brittle and a yellowish color.
• Dyeing colors the cuticle and the cortex
of the hair shaft.
• Treated hair will have unique
characteristics.
Racial Differences
• Each racial group has hair with unique
physical characteristics.
• These characteristics, however, will not
apply to all individuals in these groups.
• Sometimes it is impossible to identify
which racial group a hair belongs to.
Medullary Index
• The percentage or fraction of the hair’s
width occupied by the medulla
• [between 0 and 1]
Medullary Index?
Animal Hair and Human Hair
• Animals: Medullary Index of 0.5 or higher.
• Humans: Medullary Index of 0.33 or lower.
• Pigmentation in animal hair
is denser toward the
medulla. In Humans it tends
to be denser toward the
cuticle.
• Unlike human hair, animal
hair abruptly can change
colors in banded patterns.
21
Animal Hair and Human Hair
Animal Hair and Human Hair
• The Cuticles
Spinous
Coronal
Imbricate
• The outermost layer of the hair shaft (the
cuticle), is typically different in animals and
humans.
• Animals have a spinous or coronal cuticle.
• Humans have an imbricate cuticle.
Using Hair in an Investigation
• Macroscopic investigation – length, color,
texture.
• Microscopic investigation – Detail
• Phase contrast microscopy - dyes
• Electron microscopes – hair interior
Testing for Substances in the
Hair Shaft
• Chemicals that the skin absorbs often can be
detected by analysis of the hair shaft.
• A forensic scientist can perform chemical tests
for the presence of various substances.
• The hair shaft can be examined in sections to
establish a timeline for exposure to toxins.
• Neutron Activation Analysis (NAA) can
determine concentrations of substances in the
sample.
Testing the Hair Follicle
• Microscopic assessment of the follicle is
performed first because it is cost effective
and quick.
• If a microscopic match is found, the
follicle can be blood tested and perhaps
show the blood type.
• If a microscopic match is found, the
follicle can be DNA analyzed to provide
identification with a high degree of
confidence.