forensic science 2 hair & hair identification. hair there are millions of hairs scattered across...
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FORENSIC SCIENCE 2
Hair & Hair Identification
Hair
There are millions of hairs scattered across the body
Hair is all over the body expect on palms of hands, soles of feet, nipples and lips
Hair is the fastest growing tissue in the body
It’s main role is to provide minor protection Guards the head against
bumps and heat loss Eyelashes shield the eye Nasal hairs trap foreign
particles
Structure of Hair
Hair is all most entirely dead epidermis and proteins
The central core is the medulla, which is surrounded by a bulky cortex, which is further covered by a cuticle
The cuticle is formed by a single layer of cells that overlap one another like shingles on a roof
Structure of Hair
The cuticle is the most heavily keratinized (proteins) part of the hair to provide strength
As the hair lengthens the cuticle begins to wear away allowing the inner hair region to “frizz” out – this is known as a split end
Other Structures of Hair
Arrector pili are small bands of smooth muscles on each side of the hair root
When these muscles contract (as in cold or frightened) the hair is pulled upright
This phenomenon can especially be seen in a frightened cat
Hair Variety
Hair comes in a variety of sizes and shapes Short and stiff in the
eyebrows Long and flexible on the
head Nearly transparent in
some areasHair pigment is made
by melanocytes in the hair bulb
Varying types and amounts of melanin account for all types of hair colors from pale blond to pitch black
Hair Variety
When the hair is perfectly round, the hair tends to straight and coarse
When the hair shaft is oval hair is smooth and silky and the person has wavy hair
When the hair shaft is flat and ribbon-like, the hair is curly or kinky
The physical appearance of hair can be affected by nutritional status and intentional alteration (heat curling, perms, straightening, etc.).
Hair Identification Basics
Characteristics of the cuticle is important in distinguishing between hairs of different species but is often not useful in distinguishing between different people.
Distribution of the cortex is perhaps the most important component in determining from which individual a human hair may have come.
Hair Identification Basics
In order to test hair evidence for DNA, the root must be present.
Hairs that are forcibly removed are most likely to contain DNA
Hair Identification
The first step is to determine whether the hair in question originated from an animal or a human being.
If the hair originated from an animal, it is possible to further identify it to a particular type of animal.
If it originated from a human, the next step is to determine what region of the body it came from
Hair Identification
The hair in question is then analyzed to determine if it was naturally shed or forcibly removed
Naturally shed hairs, such as a head hair dislodged through combing, display undamaged, club-shaped roots.
Hair forcibly removed from the scalp will exhibit stretching and damage to the root area.
Forcibly removed hairs may have tissue attached.
Other Identifying Elements
Hair can also be analyzed for race determination
CaucasianCan be of fine to medium coarseness, are generally straight or wavy in appearance, and exhibit colors ranging from blonde to brown to black. The hair shafts of Caucasian hairs vary from round to oval.
Asian Are regularly coarse, straight, and circular in cross section, with a wider diameter than the hairs of the other racial groups. The outer layer of the hair, the cuticle, is usually significantly thicker than the cuticle of African and Caucasian hairs. Asian hair can have a characteristic reddish appearance as a product of its pigment.
Other Identifying Elements
African Are regularly curly or kinky, have a flattened cross section, and can appear curly, wavy, or coiled. The density of the pigment in the hair shaft may be so great as to make the hair opaque. A African hair shaft exhibits variation or apparent variation in diameter because of its flattened nature and the manner in which it lies on the microscope slide.
Other Identifying Elements
A hair that has been chemically combined can also be determined
Hairs that have been obtained by a decomposing body can be determined