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Forensics Unit 2 Notes - Chapter 5 – Hair
I.
Form and Structure of Hair
a. Must understand form and structure or morphology of hair
b. Hair- made of mostly protein polymers- many identical repeating units (natural or synthetic)
c. Cuticle- tough, clear outside covering of hair shaft
i. Three types
1. Imbricate- looks like broken glass
2. Spinous- looks like staked spines (thin cylinders)
3. Coronal- looks like stacked crowns
d. Cortex- middle layer, gives strength and mass
i. Keratin-tough protein polymer made up of about 20 amino acids
e. Medulla- spongy interior, appears as a canal
i. Patterns vary between species
1. Intermittent, Fragmented, Continuous, stacked, absent
Intermittent or interruptedFragmentedContinuousStackedAbsent—not present-
ii. Medullary Index (MI)- diameter of the medulla and divide it by the diameter of the hair.
1. Medullary index for human hair is generally less than 1/3.
2. For animal hair, it is usually greater than 1/2.
f.
II.
Cross sections- risky to assign racial characteristics to hair however…
i. Round- Asian or Native American (straight hair)
ii. Oval- European, Mexican and Middle Eastern (wavy to curly hair)
iii. Crescent moon- African (kinky hair)
g. Roots
Use in Forensics
a. Association- link between an unknown sample and a known sample
b. Questioned- sample of unknown origin
i. Hair found on jacket but do not know hose head it cam from
c. Exemplar- sample of known origin
i. hair was taken from so-and-so’s scalp (victim, suspect…)
d. A chemical indicator
i. Ingested chemicals are deposited in the cortex
e. Many drugs and their metabolites can be detected in just a few millimeters of hair
f. Metabolites- a specific product of a substance, formed by chemical processes in the body
g. Some analysis may give a false positive b/c hair can absorb chemicals from your surroundings
h. False positive- a test result that comes out positive when it should not
i. Ex: absorption of smoke from crack does not mean that crack was smoked