Forensic Science
http://media.popularmechanics.com/images/PMX0706FORENSICSHairSmall.jpg
Presentation developed by T. Trimpe 2006 http://sciencespot.net/
Biology of Hair
Hair is composed of the protein keratin, which is also the
primary component of finger and toe nails.
Hair is produced from a structure called the hair follicle.
Humans develop hair follicles during fetal development, and
no new follicles are produced after birth.
.
Hair color is mostly the result of pigments, which are
chemical compounds that reflect certain wavelengths of
visible light.
In order to test hair evidence for DNA, the root must be
present.
Sources: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair & http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric1.htm#Index%20(Hairs)
Biology of Hair
• Hair shape (round or oval) and texture (curly or
straight) is influenced heavily by genes. The
physical appearance of hair can be affected by
nutritional status and intentional alteration (heat
curling, perms, straightening, etc.)
• The body area (head, arm, leg, back, etc.) from
which a hair originated can be determined by the
sample’s length, shape, size, color, and other
physical characteristics. Hair serves the function
of protection of skin and reduction of friction
The 3 Phases of Hair Growth
• Anagen phase – initial growth where the
follicle actively produces hair. 6 years
• Catagen Phase – a transition phase where
the root bulb starts getting pushed out of
the follicle: lasts 3 weeks.
• Telogen phase – the dying phase of
pushing the hair out of the follicle and the
hair is shed. Lasts 6 weeks
• Then the cycle starts again if the follicle is
healthy. Sheading hair is natural.
Hair Growth Phases
Anatomy of a Hair
bsapp.com
Follicle
• Hair is an appendage of
the skin that grows out of
a hair follicle.
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The follicle contains more than
enough cells for simple DNA
Analysis. This is a follicular tag.
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Root
• The length of a hair extends
from the root embedded in
the follicle.
• A single root
contains
sufficient DNA
for analysis
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Hair Structure
Hair is composed of three principal parts:
Cuticle – outer coating composed of overlapping scales
Cortex – protein-rich structure around
the medulla that contains pigment
Medulla – central core
(may be absent)
The structure of hair has been compared to that of a pencil with the
medulla being the lead, the cortex being the wood and the cuticle
being the paint on the outside.
http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair
Hair Structure
Cuticle
The outside covering.
The cuticle varies in:
• Its scales,
How many there are per centimeter,
How much they overlap,
Their overall shape, and
How much they protrude from the surface
• Its thickness, and
• Whether or not it contains pigment.
Characteristics of the cuticle may be important in distinguishing
between hairs of different species but are often not useful in
distinguishing between different people.
Info: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair
Image: http://www.hairdressersus.com/micro/Image5b.jpg
Hair Cuticle Scales
• These scales are formed from
special cells that are hardened and
flattened while progressing from
the follicle. They form the same
surface as your fingernails
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Hair Structure
Cortex surrounding around the medulla (middle layer)
The cortex varies in:
• Thickness
• Texture
• Color
• Distribution of the cortex is perhaps the most important component
in determining from which individual a human hair may have come.
This is the layer of the natural color of the hair.
• Microscopic examination can also reveal the condition and shape of
the root and tip.
Info: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair
Image: http://www.extrapersonality.com/hair.html
Cortex Colors
Hair Structure
Medulla - The center of the hair
The medulla may vary in:
• Thickness
• Continuity - one continuous structure
or broken into pieces
• Opacity - how much light is able to
pass through it
• It may also be absent in some species.
Like the cuticle, the medulla can be important for
distinguishing between hairs of different species, but often
does not lend much important information to the
differentiation between hairs from different people.
http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair
http://www.bfro.net/images/whatis/figures/Fig.%203%20with%20caption.jpg
Pigment granules are absent in
grey hairs
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Medulla
• a collection of cells which appears as
a canal running though the center of
the hair
• the medulla is the most predominant
hair feature in many species
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Types of Medulla: ContinuousInterrupted-Fragmented
.
Serial medulla is the term used to
a describe multiple medulla
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within a single hair
Types of Medulla
Medullary Index
• The medullary index is an estimate of the width
of the hair
• taken up by the medulla; it is usually expressed
as a fraction. The index generally has a value
• less than 1/3 for humans; for most other animals
the value is 1/2 or greater.
Medulla:
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Forensics Can Differentiate the
Species of the Hair
• The well trained forensic microscope
technician can easily tell if a trace
evidence hair at a crime scene belongs to
a human or a rat, cat or bear!
• Take a look at the following slides and see
how different they are !!
Human Hairs
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Horse Hair
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Dog Hair
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Cat Hair
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Mouse Hair
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Rabbit Hair
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Deer Hair
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Cow Hair
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Special Conditions of Hair
The following slides show the
ends of several different species
of hairs
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Natural Tip
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Fallen Out Hairs
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Pulled Out-By the Root
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Broken-Torn
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Cut Hair
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Fiber Evidence
A fiber is the smallest unit of a textile material that has a length many times
greater than its diameter. A fiber can be spun with other fibers to form a yarn that
can be woven or knitted to form a fabric.
The type and length of fiber used, the type of spinning method, and the type of
fabric construction all affect the transfer of fibers and the significance of fiber
associations. This becomes very important when there is a possibility of fiber
transfer between a suspect and a victim during the commission of a crime.
Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing
can be very helpful to an investigation, whereas the matching of common fibers
such as white cotton or blue denim fibers would be less helpful.
The discovery of cross transfers and multiple fiber transfers between the suspect's
clothing and the victim's clothing dramatically increases the likelihood that these
two individuals had physical contact.
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Fiber%20Evidence
Natural Fibers
Many different natural fibers that come from plants and animals are used in the
production of fabric.
Cotton fibers are the plant fibers most commonly used
in textile materials
The animal fiber most frequently used in the
production of textile materials is wool, and the most
common wool fibers originate from sheep.
http://www.fireflydiapers.com/articles/diaperarticle_naturalfibersabsorb.htm
Synthetic Fibers
More than half of all fibers used in the production of textile
materials are synthetic or man-made.
Nylon, rayon, and polyester are all examples of synthetic
fibers.
Cross-section of a
man-made fiber
Fibers under a microscope
Images: http://www.trashforteaching.org/phpstore/product_images/YarnWS.JPG
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Fiber%20Evidence
http://www.jivepuppi.com/images/fiber_evidence.jpg
Synthetic (man made) fibers are made by
collecting small molecules call monomers
(single functional molecule) and connecting
them together to make polymers (many
molecules connected chemically). This is the
realm of Organic Chemistry.
Polymers can be natural like cellulose and
rubber. LINK
Synthetic Polymers are man made
molecules like nylon, rayon and all plastics.
It is used in clothing, carpets… try to think
of all plastics in your world…..
It’s time to examine
some hairs and fibers!
http://micro.magnet.fsu.edu/primer/techniques/polarized/gallery/images/humansmall.jpg
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?
Can you identify the types of fibers shown?
Think About It …
(1) Which samples are natural fibers?
(2) Which samples are synthetic fibers?
(3) What characteristics can be used to identify fiber samples?
Answer
Keys
http://micro.magnet.fsu.edu/primer/techniques/polarized/gallery/images/humansmall.jpg
Types of Animal Hairs - Key
A
Cat
B
Horse
C
Pig
D
Human
G
E
Deer
F
Dog
Rabbit
H
Rat
I
Human
Types of Fibers - Key
Acrylic Yarn
Cotton Yarn
Nylon Rope
Polyester Yarn
Rayon Rope
Wool Yarn
Hair & Fiber Identification Lab
Directions:
Your team will need to use a microscope
to document all the hairs and fibers in
your set.
Write the name of the hair or fiber on the
line and then draw what you see under
medium or high power. Be sure to
indicate the power of magnification!
Add a description that highlights the
unique characteristics of each hair and
fiber sample.
Pay attention to details to help you
identify samples during the Hair & Fiber
Challenge activity.