Chapter 3: Hair Analysis

Chapter 3: Hair analysis:

• Identify the various parts of a hair.

• Describe variations in the structure of the medulla, codex, and cuticle.

• Identify the various parts of a hair.

• Describe variations in the structure of the medulla, cortex, and cuticle.

• Distinguish between human and nonhuman animal hair.

• Determine if two examples of hair are likely to be from the same person.

• Explain how hair can be used in a forensic investigation.

• Distinguish hairs from individuals belonging to broad facial categories.

• Vocabulary:

  • Comparison Microscope.

  • Cuticle

  • Gas chromatography

  • Hair follicle.

  • Hair shaft

  • Keratin

  • Medulla.

  • Melanin granules.

  • Mitochondrial DNA (mDNA)

  • Nuclear DNA.

Introduction

• A hair without the follicle and its nuclear DNA cannot provide individual evidence.

• Hair can yield class evidence.

• Chemical tests performed on hair can reveal drugs, toxins, heavy metals, and nutritional deficiencies.

• mtDNA from hair can reveal some of a suspect’s or victim’s family relationships.

History of Hair Analysis

• 1883: Alfred Swaine Taylor and Thomas Stevenson covered hair in a forensic science text.

• 1910: Victor Balthazard and Marcelle Lambert published a comprehensive study of hair.

• 1934: Dr. Sydney Smith analyzed hairs side by side using a comparison microscope.

• Today: Standard procedures of hair analysis include microscopic examination and DNA analysis.

The Functions of Hair

• Regulates body temperature.

• Decreases friction.

• Protects against sunlight.

• Acts as a sense organ.

• Humans are born with about 5 million hair follicles.

The Structure of Human Hair

• Human hair consists of a follicle and a shaft.

• The hair shaft is made up of three layers:

  • An inner medulla: The central core of a hair fiber.

  • A cortex: The region of a hair located outside of the medulla containing granules of pigment.

  • An outer cuticle: The tough outer layer covering of a hair composed of overlapping scales.

• The cuticle is a transparent outer layer of the hair shaft.

Types of Medulla

• Continuous:  One unbroken line of color.

Types of Hair

• In humans, hair varies from person to person, and even varies depending on its location on a particular person.

• For an individual person, hair can vary based on its location on the body.

• To compensate for inconsistencies that occur, 50 hairs are usually collected from a suspect’s or victim’s head.

The Life Cycle of Hair

• Hair proceeds through three stages as it develops.

• Anagen stage (80-90% of hair)

  • Hair actively grows

  • Cells around the follicle rapidly divide and deposit materials in the hair.

  • Lasts approximately 1000 days

• Catagen stage (2% of hair)

  • Hair grows at a lower rate and changes (perhaps turning gray)

• Telogen stage (10-18% of hair)

  • The hair follicle is dormant and hair is easily lost.

Treated Hair

• When a person chemically treats his or her hair, traces of the chemicals used remain.

• Also creates subtle changes that can be detected only by using a microscope.

• Bleaching

  • Disturbs the scales on the cuticle

  • Removes pigment

  • Leaves hair brittle and yellowish

  • Dyeing colors the cuticle and the cortex. 

There are some key physical characteristics to hair.

• European: Gently straight or wavy. Small and evenly distributed. Oval or round of moderate diameter with minimal variation. Color may be blonde, red, brown, or black.

• Asian: Straight. Densely distributed. Round with large diameter. Shaft tends to be coarse and straight: thick cuticle, continuous medulla; color black.

• African: Kinky, curly, or coiled; shaft may be buckled. Densely distributed, clumped, may differ in size and shape. Flattened with moderate to small diameter and considerable variation.

Animal hair and human hair

• Animal hair and human hair have several differences including:

  • The pattern of pigmentation.

  • The medullary index.

  • The cuticle type.

Hair cuticles.

• The cuticle of the hair shaft cna help distinguish human hair from other animal hair.

Electron microscopes direct a beam of electrons at a sample. Electron microscopes provide magnification of 50,000 times or more.

Hair examination and testing

• DNA is extracted and amplified using PCR.

• DNA is profiled using an automated process.

• mDNA can be used to establish a genetic relationship through the mother.

• Suspects can be excluded if their mtDNAv is not consistent with the crime-scene mtDNA.

Summary

• Hair is a form of evidence that has been used in forensic analysis since the late 19th century.

• Hair is a characteristic shared by all mammals and functions in temperature regulation, reducing friction, protection from light, and as a sense organ.

• Hair consists of a follicle embedded in the skin that produces the shaft.

• Hair consists of a follicle embedded in the skin that produces the shaft.The shaft itself is composed mainly of a protein called keratin, which gives hair its strength and resilience.