Biology of Hair. Hair is composed of the protein, which is also the primary component of finger and toe.

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1 Prof. J. Dodd Forensic Science Biology of Hair Hair is composed of the protein, which is also the primary component of finger and toe. Hair is produced from a structure called the hair. Humans develop hair follicles during development, and no new follicles are produced after birth. Hair color is mostly the result of, which are chemical compounds that reflect certain wavelengths of visible light. Hair (round or oval) and (curly or straight) is influenced heavily by. The physical appearance of hair can be affected by status and intentional (heat curling, perms, straightening, etc.). The (head, arm, leg, back, etc.) from which a hair originated can be determined by the sample s length, shape, size, color, and other physical characteristics. In order to test hair evidence for, the must be present. Sources: & 1

2 Hair Structure Hair is composed of three principal parts: The structure of hair has been compared to that of a pencil with the medulla being the lead, the cortex being the wood and the cuticle being the paint on the outside. Hair Structure Cuticle The cuticle varies in: Its, How many there are per centimeter, How much they overlap, Their overall shape, and How much they protrude from the surface Its, and Whether or not it contains. Characteristics of the cuticle may be important in distinguishing between hairs of different but are often not useful in distinguishing between different. Info: Image: 2

3 Hair Structure Cortex The cortex varies in: Distribution of the cortex is perhaps the Microscopic examination can also reveal the condition and shape of the and. Info: Image: Hair Structure Medulla The medulla may vary in: - one continuous structure or broken into pieces - how much light is able to pass through it It may also be in some species. Like the cuticle, the medulla can be important for distinguishing between hairs of different species, but often does not lend much important information to the differentiation between hairs from different people

4 Medulla Patterns Is It Human or Animal? human hair generally <1/3 animal hair >=1/2 human normally cylindrical 4

5 Hair Comparison color length diameter presence or absence of distribution, shape & color intensity of pigment granules dyed hair has color in cuticle & cortex bleaching removes pigment & gives yellow tint 5

6 Hair is Can often determine body area of origin Can often determine racial origin African kinky with dense uneven pigment flat to oval in shape Caucasian straight or wavy fairly evenly distributed pigment oval to round shape Shedding vs. Removal By Force Presence of follicular tissue on root indicative of forcible removal by a person by a comb 6

7 Shedding vs. Removal By Force Shedding vs. Removal By Force Shedding Removal by Force 7

8 Collection of Hair Evidence Questioned hairs must be accompanied with an adequate number of From From Representative control samples 50 full-length hairs from all areas of scalp 24 full-length pubic hairs 8

9 Objectives - Distinguish between the different types of human made and natural fibers. - Define a polymer and relate polymers to the formation of fibers. - Identify distinguishing characteristics of fiber evidence. - Summarize how fiber evidence has been used the Jeffrey MacDonald cases. Fibers Fibers are all around us in our clothes, carpets, curtains, and all sorts of fabrics and fillers the types of natural and manmade fibers, their composition and formation how fibers in cloth can provide production and history information of the cloth 9

10 What is a fiber? Simply put, long thin filaments at least SEM of different fibers 10

11 Polymers! Long chains of repeating smaller sub units, called monomers Fibers Synthetic made of polymers that do not occur naturally polyesters polyamides 11

12 LET S MAKE SOME POLYESTER! Polyester is a synthetic fiber that is derived from chemicals, such as oil derived petrochemicals. It Stitching characteristics 12

13 SEM Zoom Not just for clothing Polymer based materials that are made of fibrous material don t have to just be associated with what we wear. Garbage Bags- Striations Duct Tape- Tears 13

14 Stitching characteristics Fibers Fibers can be classified into one of three main groupings depending upon how they are produced: (1) (2) (3) 14

15 Fibers Classified according to their origin vegetable or cellulose based Cotton, Jute, Hemp animal or protein based Wool, Mohair, Silk mineral class Asbestos cont Fibers do not soften when heat is applied Particularly susceptible to (mildew & rot) cellulose based decomposed by aerobic bacteria & fungi protein based decomposed by bacteria and molds moths, carpet beetles, termites, silverfish 15

16 Natural Fibers Many different fibers that come from plants and animals are used in the production of fabric. fibers are the plant fibers most commonly used in textile materials The animal fiber most frequently used in the production of textile materials is, and the most common wool fibers originate from sheep. Fibers derived from naturally occurring polymers rayon acetate rayon fiber, cuprammonium rayon, that closely resembles silk 16

17 Fibers made of polymers that do not occur naturally polyesters polyamides Synthetic Fibers More than half of all fibers used in the production of textile materials are synthetic or -. Nylon, rayon, and polyester are all examples of fibers. Cross-section of a man-made fiber Fibers under a microscope Images: