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Hair Analysis – Part I

Hair Analysis – Part I. A Study of Trace Evidence. Morphology & Structure of Hair. Hair Morphology. Morphology: Cuticle. Protective coating made of overlapping scales, produce a characteristic pattern Scales always point toward tip of hair Not useful in individualizing human hair

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Hair Analysis – Part I

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  1. Hair Analysis – Part I A Study of Trace Evidence

  2. Morphology & Structure of Hair

  3. Hair Morphology

  4. Morphology: Cuticle • Protective coating made of overlapping scales, produce a characteristic pattern • Scales always point toward tip of hair • Not useful in individualizing human hair • Can be used for species identification

  5. Morphology: Cuticle

  6. Cuticle Types Pectinate Mosaic Diamond Imbricate Petal

  7. Morphology: Cortex • Made of spindle-shaped cells aligned in a regular array, parallel to the length of the hair • Embedded with pigment granules that give hair its color • The color, shape and distribution of the granules provide points for forensic comparison

  8. Morphology: Medulla • Canal like structure of cells that runs through the center of the cortex

  9. Medulla • Medulla vary between individuals • Vary between hairs of the same individual • Some hairs have no medulla

  10. Medullary Index • Measure of the diameter of the medulla relative to the diameter of the hair shaft • Usually expressed as a fraction • Humans: medullary index < 1/3 • Animals: medullary index > 1/2

  11. Medulla of Different Species

  12. Animals RABBIT MUSKRAT COW

  13. Medulla of Different Species

  14. Medulla Related to Hair Color Very fair Light Brown Brown-Black Red

  15. Forensic Analysis of Medulla • Presence of medulla varies quite a bit: even hair to hair • Human head hairs generally have no medulla or may be fragmented ones; except Mongoloid race whose medulla is usually continuous • Most animals have medulla that is continuous or interrupted • The shape of the medulla can help identify a species • Examples: • Most animals and humans: cylindrical • Cats: pearl shape • Deer: spherical occupying whole hair shaft

  16. Variation in Hair by Sex • Stained sex chromatin in the nuclei of human cells showing the female-indicative Barr body (bright spot, top) and the male-indicative Y body (bright spot, bottom)

  17. Racial Determination Negroid Mongoloid Caucasian

  18. Hair Roots Pulled Forcibly Removed Shed

  19. Tip of the Shaft Burned Cut Razored Split

  20. Morphology: Root • Human hair grows in three developmental stages: anagen, catagen, and telogen phases

  21. Phases • 1) Anagen - Growth Phase • 2) Catagen - Transitional phase • 3) Telogen - Resting Phase

  22. Root: Anagen Phase • Initial growth phase during which hair follicle is actively producing hair, phase may last 6 years, root is flame like in appearance • When pulled this root may contain a follicular tag (rich source of DNA) Root w/ follicular tag

  23. Root: Catagen Phase • A transition phase—hair grows at a decreasing rate for two to three weeks—elongated appearance as root bulb shrinks and is being pushed out of hair follicle

  24. Root: Telogen phase • Hair growth has ended—root takes on a club-like appearance—during two-six month period, the hair will be pushed out of the follicle causing the hair to shed naturally

  25. Identification and Comparison • Establish if the hair is human or animal • Compare if the hair retrieved at the crime scene is compatible from a known hair of a particular individual • The ability to distinguish human from animal is easy when compared to that of human hair comparison • Various morphological characteristics between individuals and the same individual

  26. Identification and Comparison • Microscopic examination • Animal or human • Species of animal • Important characteristics: • Scale structure • Medullary index • Medullary shape

  27. Identification and Comparison • Scalp hair • Pubic hair • Comparison microscope • Hair from any part of the body exhibits a wide range of characteristics the examiner must have an adequate number of known hair samples that are representative of all its features

  28. Identification and Comparison • Compare • Length • Color • Diameter • Presence or absence of medulla • Distribution, shape and color intensity of the pigment granules present in the cortex • Dyed, bleached or natural hair

  29. Identification and Comparison • Dyed hair: dye color found in cuticle as well as throughout cortex • Bleaching: removes pigment from the hair and gives a yellowish tint • If there has been growth of hair since last bleach or dye treatment: natural-end is distinct in color • Hair is known to grow at an approximate rate of 1 cm/month • Therefore can estimate the time since last appointment or treatment

  30. Identification and Comparison • Morphological abnormalities; • Diseases • Deficiencies • Fungal and nit infections • If one human head hair taken from the crime scene is found to be similar to a representative hair from a suspect’s head, the odds against it from originating from another person are about 4500 to 1 • The odds of two different pubic hairs originating from two different individuals is 800 to 1

  31. What can be determined • Body areas: • Scalp hairs show little variation of diameter and have more uniform distribution of pigment color • Pubic hair are short, curly with a wide range of variations in shaft diameter and a continuous medulla • Beard hairs: coarse and usually triangular in cross-section with blunt tips from cutting or shaving

  32. What can be determined • Racial origin: • Can distinguish between Negroid and Caucasian head hair • Negroid hair: normally kinky, containing dense, unevenly distributed pigments, flat to oval in shape • Caucasian hair: straight or wavy, with very fine to coarse pigments that are more evenly distributed when compared to Negroid hair • Cross sections of Caucasian hair are oval to round in shape • These are very general in nature

  33. What can be determined • Age cannot be determined from morphology with any degree of certainty except with infant hair • Fine, short in length, have fine pigment and are rudimentary in character • Sexual discrimination at this time is not considered to be a routine forensic technique, but can be made with root tip DNA • Microscopic examination of the hair root may establish if the hair has fallen out or has been pulled out • Hair root with follicular tissue adhering to it is indicative that the hair has been pulled out

  34. What can be determined • The current approach for examination of hair is the morphological characteristics • Breakthroughs in nuclear DNA typing has extended the technology to the individualization of human hair • Examiners can link a particular human hair to an individual by characterizing the nuclear DNA in the hair root or follicular tissue adhering to the root • Higher rate of success extracting DNA from a hair in the anagen phase or anagen hairs entering the catagen phase then those in the telogen phase

  35. Collection • Crime scene hairs must always be accompanied by an adequate amount of control samples from the victim and from suspects • Hair from any one area of the body varies significantly. The questioned hairs and control hairs must come from the same area of the body

  36. Collection of Hair Specimen

  37. Collection • Forensic hair comparisons usually involve scalp or pubic hairs • Collection of 50 full length hairs from all areas of the scalp • A minimum of two dozen full length pubic hairs • In rape cases care must be taken to first comb the pubic area to remove all foreign hair present before the victim is sampled for control hair

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