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Forensic Science

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  1. Hairs & Fibers Forensic Science Presentation developed by T. Trimpe 2006

  2. Biology of Hair Hair is composed of the protein keratin, which is also the primary component of finger and toe nails. Hair is produced from a structure called the hair follicle. Humans develophair follicles during fetal development, and no new follicles are produced after birth. . Hair color is mostly the result of pigments, which are chemical compounds that reflect certain wavelengths of visible light. In order to test hair evidence for DNA, the root must be present. Sources: &

  3. Biology of Hair • Hair shape (round or oval) and texture (curly or straight) is influenced heavily by genes. The physical appearance of hair can be affected by nutritional status and intentional alteration (heat curling, perms, straightening, etc.) • The body area (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. Hair serves the function of protection of skin and reduction of friction

  4. The 3 Phases of Hair Growth • Anagen phase – initial growth where the follicle actively produces hair. 6 years • Catagen Phase – a transition phase where the root bulb starts getting pushed out of the follicle: lasts 3 weeks. • Telogen phase – the dying phase of pushing the hair out of the follicle and the hair is shed. Lasts 6 weeks • Then the cycle starts again if the follicle is healthy. Sheading hair is natural.

  5. Hair Growth Phases

  6. Anatomy of a Hair

  7. Follicle • Hair is an appendage of the skin that grows out of a hair follicle.

  8. The follicle contains more than enough cells for simple DNA Analysis. This is a follicular tag.

  9. Root • The length of a hair extends from the root embedded in the follicle. • A single root contains sufficient DNA for analysis

  10. Medulla – central core(may be absent) Cortex – protein-rich structure around the medulla that contains pigment Hair Structure Hair is composed of three principal parts: Cuticle – outer coating composed of overlapping scales 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.

  11. Hair Structure • Cuticle The outside covering. • The cuticle varies in: • Its scales, • How many there are per centimeter, • How much they overlap, • Their overall shape, and • How much they protrude from the surface • Its thickness, and • Whether or not it contains pigment. Characteristics of the cuticle may be important in distinguishing between hairs of different species but are often not useful in distinguishing between different people. Info: Image:

  12. Hair Cuticle Scales • These scales are formed from special cells that are hardened and flattened while progressing from the follicle. They form the same surface as your fingernails

  13. Hair Structure • Cortex surrounding around the medulla (middle layer) • The cortex varies in: • Thickness • Texture • Color • Distribution of the cortex is perhaps the most important component in determining from which individual a human hair may have come. This is the layer of the natural color of the hair. • Microscopic examination can also reveal the condition and shape of the root and tip. Info: Image:

  14. Cortex Colors

  15. 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. Hair Structure • Medulla - The center of the hair • The medulla may vary in: • Thickness • Continuity - one continuous structure or broken into pieces • Opacity - how much light is able to pass through it • It may also be absent in some species.

  16. Pigment granules are absent in grey hairs

  17. Medulla • a collection of cells which appears as a canal running though the center of the hair • the medulla is the most predominant hair feature in many species

  18. Types of Medulla: Continuous-Interrupted-Fragmented . Serial medulla is the term used to a describe multiple medulla within a single hair

  19. Types of Medulla

  20. Medullary Index • The medullary index is an estimate of the width of the hair • taken up by the medulla; it is usually expressed as a fraction. The index generally has a value • less than 1/3 for humans; for most other animals the value is 1/2 or greater.

  21. Medulla:

  22. Forensics Can Differentiate the Species of the Hair • The well trained forensic microscope technician can easily tell if a trace evidence hair at a crime scene belongs to a human or a rat, cat or bear! • Take a look at the following slides and see how different they are !!

  23. Human Hairs

  24. Horse Hair

  25. Dog Hair

  26. Cat Hair

  27. Mouse Hair

  28. Rabbit Hair

  29. Deer Hair

  30. Cow Hair

  31. Special Conditions of Hair The following slides show the ends of several different species of hairs

  32. Natural Tip

  33. Fallen Out Hairs

  34. Pulled Out-By the Root

  35. Broken-Torn

  36. Cut Hair

  37. Fiber Evidence A fiber is the smallest unit of a textile material that has a length many times greater than its diameter. A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric. The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations. This becomes very important when there is a possibility of fiber transfer between a suspect and a victim during the commission of a crime. Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing can be very helpful to an investigation, whereas the matching of common fibers such as white cotton or blue denim fibers would be less helpful. The discovery of crosstransfers and multiple fiber transfers between the suspect's clothing and the victim's clothing dramatically increases the likelihood that these two individuals had physical contact.

  38. Natural Fibers Many different natural fibers that come from plants and animals are used in the production of fabric. Cotton fibers are the plant fibers most commonly used in textile materials The animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep.

  39. Fibers under a microscope Synthetic Fibers More than half of all fibers used in the production of textile materials are synthetic or man-made. Nylon, rayon, and polyester are all examples of synthetic fibers. Cross-section of a man-made fiber Images:

  40. Synthetic Fibers Synthetic (man made) fibers are made by collecting small molecules call monomers (single functional molecule) and connecting them together to make polymers (many molecules connected chemically). This is the realm of Organic Chemistry.

  41. Polymer Science Polymers can be natural like cellulose and rubber. LINK Synthetic Polymers are man made molecules like nylon, rayon and all plastics. It is used in clothing, carpets… try to think of all plastics in your world…..

  42. It’s time to examine some hairs and fibers!

  43. Can you identify the animal hairs shown? A B C D G E F H I • Think About It … • In which samples are we viewing the cuticle? How do they compare? • (2) In which samples are we viewing the medulla? How do they compare? • (3) What characteristics can be used to identify hair samples?

  44. Can you identify the types of fibers shown? A B C D E F • Think About It … • Which samples are natural fibers? • (2) Which samples are synthetic fibers? • (3) What characteristics can be used to identify fiber samples?

  45. Answer Keys

  46. Types of Animal Hairs - Key Cat Horse Pig Human A B C D G E F H I Deer Dog Rabbit Rat Human

  47. Types of Fibers - Key A B C Acrylic Yarn Cotton Yarn Nylon Rope D E F Polyester Yarn Rayon Rope Wool Yarn

  48. Hair & Fiber Identification Lab Directions: Your team will need to use a microscope to document all the hairs and fibers in your set. Write the name of the hair or fiber on the line and then draw what you see under medium or high power. Be sure to indicate the power of magnification! Add a description that highlights the unique characteristics of each hair and fiber sample. Pay attention to details to help you identify samples during the Hair & Fiber Challenge activity.