External Hair Structure
What part of the hair extends above the skin surface?
The hair shaft
If you take a cross section of a hair, name the outer layer, middle layer, and the innermost layer.
The outer layer is the cuticle. The middle layer is the cortex. The innermost layer is the medulla.
What type of cuticle pattern do human hairs have?
Imbricate
What part of the hair contains nuclear DNA and living cells?
The hair follicle
What is the name of the structure that surrounds the hair shaft and contains living cells?
The hair follicle
What is the primary protein that hair is made of?
Keratin
What two cuticle patterns are found on animal hairs and not human hairs?
Coronal and spinous
What part of the hair contains mitochondrial DNA?
also
Which is better for identifying someone: nuclear DNA or mitochondrial DNA?
The hair shaft
and
Nuclear DNA because mitochondrial DNA is only inherited from an individual's mother and it only contains 37 genes while nuclear DNA contains 20,000-25,000 genes.
What is the name of the structure that is responsible for supplying vital nutrients to the hair?
Capillary
What are the four primary types of medulla patterns that we discussed.
Continuous, fragmented, interrupted (intermittent), and absent (missing).
How is the hair root different on a human hair compared to an animal hair?
On a human hair, the root is shaped like a club and the roots of animal hairs are highly variable.
If hair is forcibly removed, then what is attached to the hair strand?
The hair root along with a tiny section of the hair follicle called a follicular tag.
What layer of skin is the follicle primarily located in?
The Dermis
What substance determines hair color and where is that substance found in a hair strand?
The amount of melanin in the cortex.
How can forensic scientists tell if a hair strand belongs to an animal or human based on the medulla?
The medullary index is 0.33 or less for humans but it is 0.5 or greater for animals.
How can forensic scientists tell if someone dyed their hair? (There are two correct ways that you can answer this question)
1. The hair shaft will have a painted color and the cuticle/cortex of the hair strand take on the color of the dye as well.
2. There is naturally colored hair closest to the scalp and a dyed color on the other portion of the hair strand.
Describe the location of the papilla in each of the three phases of hair growth.
The papilla is inside the follicle in the first phase (anagen). The papilla is outside the follicle but still attached to it in the second phase (catagen). The papilla completely detaches from the follicle in the third phase (telogen).
What determines if hair is straight, wavy. or curly?
The alignment of protein bonds in the cortex.
Describe something found in the cortex of animal hair that is not found in the cortex of human hair.
Melanin forms dark clumps (spots) in the cortex of animal hair and these dark spots are not found in the cortex of human hair.
How can forensic scientists determine where someone has lived or traveled to from a hair strand?
By comparing the isotopic ratio from the hair to the isotopic ratio found at several locations.