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Chapter 5 - Hair
Transcript of Chapter 5 - Hair
You will understand that:
DNA From Hair
Chapter 5 - Hair
Hair is class evidence.
Hair can back up circumstantial evidence.
Hair absorbs and adsorbs substances both from within the body and from the external environment.
You will be able to:
Describe the structure of a hair.
Explain the difference between human and animal hair.
Explain which characteristics of hair are important for forensic analysis.
Assess the probative value of hair samples.
The cortex gives the hair its shape.
Outermost layer of hair, covered with scales.
Determined by measuring the diameter of the medulla and dividing it by the diameter of the hair.
Human medulla may be continuous, fragmented, or absent.
The medulla is the hair core that is not always visible. The medulla comes in different types and patterns.
Grows about 0.4 mm per day, or 1 cm per month; approximately one-half inch per month
Dyed hair has color in cuticle and cortex
Human roots look different based on whether they have been forcibly removed or they are telogen hairs and have fallen out. Animal roots vary, but in general have a spear shape.
Can be straight, curly, or kinky, depending on the cross-section, which may be round, oval, or crescent-shaped.
The root contains nuclear DNA.
50 full-length hairs from all areas of scalp
Questioned hairs must be accompanied by an adequate number of control samples.
Collection of Hair
Collections must be taken from different locations on the body to get an accurate timeline.
Can provide information on the individual’s history of drug use or evidence of poisoning
Napoleon died in exile in 1821. By analyzing his hair, some investigators suggest he was poisoned by the deliberate administration of arsenic; others suggest that it was vapors from the dyes in the wallpaper that killed him.
For additional information about hair and other trace evidence, check out truTV’s Crime Library at:
More about Hair
Cuticle: outside covering, made of overlapping scales
Cortex: inner layer made of keratin and embedded with pigment; also contains air sacs called cortical fusi
Medulla: inside layer running down the center of the cortex
The scales point toward the tip of the hair.
Scales differ among species of animals and are named based on their appearance.
The three basic patterns are:
It has two major characteristics:
Cortical fusi: air spaces, usually found near the root but may be found throughout the hair shaft
Melanin: pigment granules that give hair its color
Intermittent or interrupted
Medullary index for human hair is generally less than 1/3.
For animal hair, it is usually greater than 1/2.
Anagen—hair is actively growing; lasts up to 5 years
Catagen—hair is not growing; a resting phase
Telogen—follicle is getting ready to push the hair out; lasts two to six months
Distribution, shape, and color intensity of pigment granules
Presence or absence of medulla
Bleaching removes pigment and gives a yellow tint
If the hair has been forcibly removed, some follicular tissue containing DNA may be attached.
The hair shaft contains abundant mitochondrial DNA, inherited only from the mother.
This process is more difficult and more costly than using nuclear DNA.
It can be typed by comparing relatives if no DNA from the body is available.
From others who may have deposited hair at the scene
From possible suspects
Easy to collect and store
Is externally available