Unit 2 Study Guide: Hair Analysis

Hair Analysis Vocabulary

  • Comparison Microscope: A device for side-by-side examination of two samples, commonly used in hair analysis.

  • Cortex: The thickest layer of the hair shaft, containing fibrous protein and melanin granules that affect hair color and texture.

  • Cuticle: The outermost layer of hair, made up of overlapping scales that protect inner layers and help in species identification.

  • Gas Chromatography: A chemical analysis method used to separate and analyze vaporized compounds in hair for substance detection.

  • Hair Follicle: The structure that produces hair, containing DNA and blood vessels, crucial for obtaining nuclear DNA.

  • Hair Shaft: The non-growing part of hair that extends above the skin surface, primarily made of keratin.

  • Isotope: Variants of a chemical element with the same number of protons but different numbers of neutrons, affecting mass.

  • Isotope Signature: The unique ratio of isotopes in a sample that can help determine sources or origins.

  • Isotope-ratio mass spectrometry (IRMS): A technique that measures the ratios of stable isotopes for individual evidence related to origin or diet.

  • Keratin: A fibrous protein making up the structure of hair, providing strength and resilience.

  • Medulla: The central core of the hair, varying in presence among different hair types, aiding in identification.

  • Melanin granules: Pigment granules in the cortex influencing hair color and important for comparative analysis.

  • Mitochondrial DNA: DNA found in mitochondria, inherited maternally, useful for determining familial relationships but less specific than nuclear DNA.

  • Nuclear DNA: DNA in the nucleus of a cell, providing unique genetic information for individual identification.

  • Neutron activation analysis (NAA): A sensitive method measuring element concentration in a sample, useful for identifying substances in hair.

Explain why hair serves as a valuable source of evidence (characteristics, source of DNA, chemical testing)

Hair is valuable evidence because:

  • Characteristics: Hair easily adheres to surfaces, allowing transfer to victims or crime scenes, and has a tough outer coating.

  • Source of DNA: Hair with an attached follicle contains nuclear DNA for individual identification, while hair without a root contains mitochondrial DNA useful for familial connections.

  • Chemical Testing: Techniques like gas chromatography and isotope ratio analysis can detect substances ingested or absorbed, aiding investigations.

Describe how techniques in the analysis of hair have changed throughout history. (Timeline starting with the 1800s-2000s)

  • 1800s: Early recognition of hair analysis as trace evidence.

  • 1900s: Comprehensive studies began in France, and the comparison microscope was introduced for detailed examination.

  • 2000s: Advocacy for improved technician training and equipment certification emerged, and reliance on solely microscopic hair analysis decreased due to subjectivity and error potential.

Discuss the functions and structure of hair. Be able to label/identify the structures.

  • Functions:

    • Regulates body temperature.

    • Decreases friction on skin.

    • Protects against sunlight exposure.

  • Structure:

    • Follicle: Contains the papilla with blood vessels and DNA.

    • Hair Shaft: Non-growing part composed mainly of keratin.

What are the 3 life cycles of hair?

  1. Anagen Stage: Lasts approximately 1,000 days; 80-90% of hair is in this phase.

  2. Catagen Stage: Growth ceases, and the follicle recedes; 2% of hair is in this phase.

  3. Telogen Stage: Dormant/resting hair that is eventually lost; 10-18% of hair is in this phase.

Describe and list the structure of human hair.

  • Structures:

    • Follicle: Produces hair, contains papilla, DNA, and blood vessels.

    • Hair Shaft: Non-growing part, made of keratin, extends above the skin surface.

    • Cuticle: Outermost layer with overlapping scales.

    • Cortex: Thickest layer containing melanin.

    • Medulla: Central core, may vary in presence.

Describe the various characteristics of human hair.

  • Varies in shape, length, diameter, texture, and color.

  • Treated hair may show effects from bleaching and dyeing.

  • Key physical characteristics can vary between ethnicities.

Describe the differences between nonhuman and human hair.

  • Pigmentation: Human hair typically has consistent color, while nonhuman hair may vary.

  • Medullary Index: The ratio of medulla diameter to hair diameter differs significantly.

  • Cuticle Structure: Human cuticles are flattened and narrow compared to some nonhuman hairs.

How do you properly collect hair that is attached and unattached from a crime scene?

  • Firmly Attached Hair: Leave intact; document location, photograph, and package clothing with hair.

  • Unattached Hair: Photograph in situ, use clean forceps to collect, and place in a vial or box for analysis.

What information can be learned from forensic hair analysis using the following testing strategies?

  • Microscopic/Macroscopic Analysis: Visible characteristics are analyzed by the naked eye and further examined under microscopy for detailed features.

  • Chemical Analysis: Investigates substances absorbed or ingested, often using methods like gas chromatography.

  • DNA Analysis: Focuses on hair with follicles or roots for individual genetic evidence.

Describe the two recent advances in hair analysis.

  1. Neutron Activation Analysis (NAA): A method that uses neutrons to find out what elements are in hair, helping to match hair to a person or place.

  2. Isotope Ratio Mass Spectrometry (IRMS): A technique that checks the ratios of different types of atoms in hair to learn about a person's diet and where they come from