Chapter 13
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What are the parts of the hair shaft?
Cuticle: Outer layer, scales protect the hair. Cortex: Middle layer containing pigment granules for color. Medulla: Central canal running through the hair
What are the parts of a hair?
Shaft: Extends above the skin (cuticle, cortex, medulla). Follicle: Anchors hair in the skin. Root: Located at the base of the follicle.
Which part of the hair shaft is most resistant to chemical decomposition?
The cuticle.
Which feature of hair is most important for species identification?
The medulla.
What does the scale pattern of hair help to identify?
The species of the hair’s origin.
Where are the pigment granules that give hair its color located?
In the cortex.
What is the central canal running through many hairs called?
The medulla.
How can animal hair be distinguished from human hair?
By examining the medulla and the scale pattern.
How does the medullary index of human hair differ from that of most animals?
Human hair: Medullary index is less than 1/3. Animal hair: Medullary index is 1/2 or greater.
What are the phases of hair growth?
Anagen Phase: Active growth. Catagen Phase: Transitional phase; root shrinks. Telogen Phase: Resting phase; hair is shed.
How can medullae be categorized?
Interrupted or Absent: Gaps or no medulla. Fragmented: Uneven medulla segments. Continuous: Unbroken medulla.
What part of hair contains its scales?
The cuticle.
How does hair differ by body region?
Head Hair: Uniform diameter, longer. Pubic Hair: Shorter, curly, varying diameter. Facial Hair: Coarse, triangular cross-section.
Beard hairs are normally what shape in cross-section?
Triangular.
Nuclear DNA typing is most successful on hairs removed during which stage?
The anagen phase.
What is the most prevalent plant fiber?
Cotton.
What was the first manmade fiber?
Nylon.
How should hair and fiber evidence be collected and packaged?
Use tweezers or tape for collection. Package individually in sealed envelopes or paper bindles.
What properties of fibers are examined when comparing two fibers?
Color and diameter. Cross-sectional shape. Dye composition.
Why are forcibly removed hairs more likely to provide useful DNA?
They often have follicular tissue attached.
In which stage of growth are hairs more likely to yield DNA?
The anagen phase.
How many full-length head hairs and pubic hairs are recommended for reference samples?
50 head hairs. 24 pubic hairs.