Chapter 12: Forensic Hair Examinations Flashcards
What types of hairs do animals have?
Animal hair is classified as “nonhuman”. Animals have three types of hairs:
- Guard hairs: large, stiff hairs that make up the outer part of the animals coat
Guard hairs often contain a shield: widening in the upper half of the shaft
- A subshield structure: may be found, a narrowing of the hair to slightly less than the normal, nonshield shaft diameter
- Fur hairs: fill in the rest of the coat providing warmth and bulk. Thinner, soft hairs
- Vibrissa: whiskers. Short-long stiff, often white around the snout and muzzle
What are the growth stages of hairs?
There are three phases of growth.
Anagen (actively growing) phase is where the follicle produces new cells and pushes them up the hair shaft as they become incorporated into the structure of the hair.
Catagen phase is when the follicle begins to shut down production of cells. The cells begin to shrink and the root condenses into a bulb-shaped structure called a root bulb or club root.
Telogen phase is the resting phase for the follicle. Cell production has ceased and the root has condensed into a bulb. It is held in place only by a mechanical connection at the base of the root/follicle. When the mechanical connection is broken, the follicle is triggered into the anagen phase again and the cycle renews.
How can you tell if a hair may have been forcibly removed?
You can tell if a hair was forcibly removed based on the stage of growth it was in. If the hair has a bulb root, it was in the telogen phase and we cannot state whether it came out due to normal causes or if it was forcibly removed.
However, if there is tissue from the follicle attached to the hair and/or root stretching, it may indicate forcible removal. This is because during the anagen or catagen phase, the hair and follicle are still attached through active cellular growth. The hair is still soft and nonkeratinized, which causes stretch and tissue to be connected.
This does not tell us what kind of force was used, or the circumstances around the removal.
What are some of the differences between human and animal hairs?
Animal hairs have several macroscopic characteristics that distinguish them from those of humans. Guard hairs, fur hairs, and vibrissa are amongst them. Some nonhuman hairs are also colour banded, which show abrupt colour transitions along the shaft. Scale patterns are also sometimes visible on animal hairs. Scale patterns can be viewed by making a scale cast. This is done by laying a hair on clear nail polish on a slide and removing the hair before it is completely dried. If there are scales, it will make an imprint in the polish and be visible through the microscope.
What characteristics are used to determine body area?
Different hairs from the different parts of the body have distinguishing characteristics.
Hair from the head has an even diameter, straight/curly/wavy shaft, and a usually cut tip.
Pubic hair has a diameter that varies, buckling (abrupt change in direction with/without slight twist) sometimes with extreme waviness or curl, and a usually pointed tip with razor cut.
Facial hair has a wide and even diameter, triangular cross section and some shouldering in the shaft, and a usually cut (scissors/razor) tip.
Chest hair can have an even to some variation in the diameter, wavy to curly; some more straight in the shaft, and a tip that is usually pointed.
Axillary hair is even with some variation in diameter, less wavy or curvy than the chest in the shaft, and the tip is usually pointed and may be colorless.
Limb hair is fine with some tapering in diameter, the shaft has a slight arc, and the tip is usually pointed.
Eyebrow/eyelash hair is tapering in diameter, the shaft is short with an arc, and the tip is pointed.
Why is estimating ancestry from hairs difficult?
Estimating ancestry from hairs is difficult because the categories of ancestry used in forensic hair analysis are very broad. European, Africans, and Asians are the three categories, which can include many types of sub-ancestries and is not very specific. Also, many people have mixed ancestry, and this does not account for that. Ancestral hair examination can be stereotypical and not account for diversity within groups.
Name three ways in which a hair can be cosmetically treated.
Hair can be cut/razored, dyed, braided, or shaved. When hair is bleached, the pigmentation is oxidized and colour is removed.
Why are hairs stronger in exclusion than in inclusion?
The value of microscopic hair comparisons in exclusion is higher than in associations. Microscopic hair comparisons are highly sensitive by only moderative specific tests. They have a role to play in addressing wrongful convictions.
What is a comparison microscope?
A comparison microscope is used for the examination of hair samples from a crime scene with known hairs. A comparison microscope is composed of two transmitted light microscopes joined by an optical bridge to produce a split image. Allows us to make a side-by-side comparison. This is central to the effectiveness and accuracy of a forensic hair comparison.
What is a guard hair?
Guard hairs: large, stiff hairs that make up the outer part of the animal’s coat. Guard hairs often contain a shield: widening in the upper half of the shaft. A subshield structure: may be found, a narrowing of the hair to slightly less than the normal, nonshield shaft diameter
How does the use of mtDNA assist in hair comparisons?
mtDNA can act as a complementary analysis to either confirm or dispute a hair comparison. On their own separately, it is not enough to confirm a positive identification. However, together, they can provide positive identification. mtDNA typing can often distinguish between hairs from different sources although they have similar microscopic hair characteristics.
How would you distinguish between males and females using hair?
You cannot distinguish between males and females using hair. The only exception is if there is DNA on the hair sample and you can get an XX or XY match from analysis. Short hair does not mean male nor does long hair mean female.
Can you tell how old people are by looking at their hair?
You cannot tell how old a person is by only looking at their hair. Hair can begin graying from as early as in one’s 20s. Grey hair is not an indicator of age and no other characteristics can definitely tell you a person’s age.
What are cortical fusi?
Cortical fusi are small bubbles that may appear in the cortex. When they do appear, they may be sparse, aggregated, or evenly distributed throughout the cortex. They also vary in size and shape. Many telogen root hair will have an aggregate of cortical fusi near the root bulb. It is thought that this is related to the shut down of the growth activity as the follicle transitions from catagen to telogen phase.
What are the three macroscopic parts of hair?
The three macroscopic parts of hair are the root, shaft, and top. The root is the portion that formerly was in the follicle, the proximal most portion of the hair. The shaft is the main portion of the hair. The top is the distal most portion of the hair.
