Fiber Evidence Hair Notes 4.1.

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Presentation transcript:

Fiber Evidence Hair Notes 4.1

Hair Evidence The presence of hair can associate a suspect to a victim or a suspect/victim to a crime scene. It is a common way to close the linkage triangle. The types, condition and number of hairs found all impact on their value as evidence in a criminal investigation.

Hair Evidence What can be determined? Whether the hair originated from a human, an animal, or is synthetic. If animal, it is possible to link it to a particular type of animal. Hairs can identify species, it is not possible to identify hairs to a specific individual. An example of this occurs when dog hairs can be associated to a particular breed but cannot be identified to a specific dog within that breed.

What other information can be gleaned from Hair? If you have the follicular tag, DNA From spectroscopy, the chemical make-up (e.g., diet, poisons, drugs) Species Body region Race Chemical treatments (dyes, bleaching, etc.) Recently cut hair vs. worn hair

What is Hair? Slender outgrowths of the skin of mammals (and only mammals) Evolved from the scales of Reptiles! Composed primarily of the protein keratin Each species possesses hair with characteristic length, color, shape, scale pattern, root appearance, and internal microscopic features.

What is Hair? Hairs grow out of pits in the skin called follicles. The base of the hair, sunk in the skin, is called the root the part that emerges from the skin is the shaft. The sebaceous glands secrete an oily substance, which lubricates the hair, waterproofs and conditions it.

What is Hair? The Hair shaft is made up of three layers Cuticle Cortex Medulla

Layer 1: The Cuticle The outermost layer A transparent, scale-like layer of overlapping cells (can you see the direction of growth?) The protective barrier for the cortex and the medulla. 

Layer 2: The Cortex composed of fibrous protein core of elongated cells contains melanin pigment responsible for giving the hair its strength, elasticity and resistance to change.  Makes up about 90 percent of the total weight of the hair. This is the layer of the hair where chemical changes take place when changing the color, waving, or relaxing the hair.

Layer 3: The Medulla The center portion of the hair shaft is also called the pith Composed of round cells, two to five rows across Thick or coarse hair usually contains a medulla. Fine hair for the most part lacks a medulla, as does naturally blonde hair.

Hair Color Melanin pigment that gives color to the hair and skin. two types of melanin Eumelanin is brown/black in color and is the most common type of melanin. This form of melanin gives color to hair shades from black to brown. Phaeomelanin is red in color and gives the yellow, ginger and red shades of hair their color. produced by cells in the cortex called melanocytes. collect and bundle pigment proteins into melanosomes. The size, type and distribution of melanosomes determine the color of the hair. What determines the hue we see is the ratio of eumelanin to phaeomelanin.

3 Phases of Hair Growth Hair follicles undergo a cyclical growth pattern passing through 3 stages: Anagen - the growth phase Catagen – intermediate phase Telogen - the resting phase microscopic characteristics can determine the phase of growth of the hair.

Phase #1: Anagen actively growing materials are deposited into the shaft by cells in the follicle. actively dividing cells around the follicle grow upward to form the major components of the shaft and accompanying root sheath. Has intact blood supply                                                 An anagen hair that has been plucked out: notice the soft, sticky tail

Phase #2: Catagen Shortest phase of hair growth Is a transition phase between the actively growing anagen and non-growing telogen An anagen hair that has been plucked out: notice the soft, sticky tail

Phase #3: Telogen dormant or resting the hair is attached to the follicle only by the root a minimal amount of force (such as that from combing) is required to dislodge the hairs                                                A normal telogen hair with a hard 'club' end, seen under (top) a light microscope and (bottom) an electron microscope

Hair Growth Facts On a Healthy Head: 80 to 90 percent of the hair follicles are in the anagen phase 2 percent are in the catagen phase 10 to 18 percent are in the telogen phase. Which phase takes the longest? Shortest? The average period of growth for scalp hair is approximately 1,000 days The average scalp has between 100,000-150,000 follicles The hair of men grows faster than that of woman Hair grows faster at night and during the summer