The Forensic Analysis of Hair

Comprehensive vocabulary flashcards covering the forensic morphology, collection methods, cuticle patterns, medullary indices, life cycle phases, racial and somatic origins, toxicology, and DNA analysis of hair.

Keratin

A strong protein resistant to chemical decomposition whose interconnecting groups form stable fibrils, making hair a durable form of physical evidence.

Melanin

The pigment granules located primarily in the cortex that give hair its color.

Hair Shaft

The portion of the hair extending above the epidermis composed of dead, cornified cells arranged in three main regions: the cuticle, cortex, and medulla.

Cuticle

The thin, translucent outer layer surrounding the hair shaft consisting of overlapping scales of hardened, keratinized tissue arranged in species-specific patterns.

Coronal Cuticle Pattern

A crown-like scale pattern found in hairs of very fine diameter, typical of rodents and rarely observed in humans.

Spinous Cuticle Pattern

A petal-like or flower petal-like scale pattern common in soft-furred animals such as cats, seals, minks, and rabbits, and never found in humans.

Imbricate Cuticle Pattern

A flattened-like scale pattern that is commonly found in human hair.

Cortex

The main body of the hair shaft composed of spindle-shaped cortical cells containing pigment granules, cortical fusi, and hair coloring.

Cortical Fusi

Air spaces of varying sizes located within the cortex near the root of mature human hair.

Pigment Granules

Small, dark, granulated structures in the cortex that vary in size, color, and distribution; in humans, they are distributed predominantly toward the cuticle.

Medulla

The central cellular core running through the center of the cortex; amorphous and often fragmented, interrupted, continuous, or absent in humans, but regular and well-defined in animal hair.

Medullary Index

The ratio calculated as $\text{Medullary Index} = \frac{\text{diameter of medulla}}{\text{diameter of hair}}$. A ratio of $< 33\%$ indicates human hair, while a ratio of $> 50\%$ indicates animal hair.

Anagenic Phase

The active initial growth phase lasting up to $6\,\text{years}$, where the follicle is attached to the root by the papilla; pulling the hair leaves a follicular tag suitable for nuclear DNA analysis.

Follicular Tag

A translucent piece of tissue surrounding the hair's shaft near the root when an anagenic hair is forcibly pulled, containing rich supplies of nuclear DNA.

Catagenic Phase

The transitional hair growth phase lasting $2\text{--}3\,\text{weeks}$, during which the hair continues to grow while the bulb shrinks.

Telogenic Phase

The final resting growth phase lasting $2\text{--}6\,\text{months}$, where the root club forms, the hair becomes naturally loose, and shedding occurs most frequently.

Control Hair Samples

Representative standard samples gathered from all pertinent body regions of the victim, suspect, and persons of interest, typically requiring $50$ head hairs and $24$ pubic hairs with roots intact.

Negroid Hair

Hair characterized by a curly texture, dense and unevenly distributed pigment, shaft diameter variations, fragmented or absent medullae, and a flattened cross-section.

Mongoloid Hair

Hair characterized by a coarse and straight shaft with little diameter variation, dense and unevenly distributed pigment, a continuous medulla, and a round cross-section.

Caucasoid Hair

Hair characterized by a straight to wavy appearance, fairly evenly distributed fine pigment, a moderate shaft diameter with little variation, and an oval cross-section.

Somatic Origin

The identification of the specific body area an evidential hair derived from (e.g., head, pubic, facial, limb, or eyelash/eyebrow), determined by distinctive morphology like cross-sectional shape and tip wear.

Hair Growth Rate

The average speed of hair shaft extension, measuring approximately $1.3\,\text{cm}$ per month, used in forensic toxicology to estimate the timeline of drug ingestion or chemical exposure.

Enzyme-Linked Immunosorbent Assay (ELISA)

An immunoassay based on an antigen-antibody interaction where an analyte or drug binds to a solid phase to produce a measurable colorimetric or fluorescent change used to detect substances in hair.

Nuclear DNA (nDNA)

Genetic material inherited from both parents that can be extracted from the root or follicular tag of an anagenic hair to achieve individualization with odds in the billions or trillions.

Mitochondrial DNA (mtDNA)

Extranuclear genetic material inherited exclusively maternally that can be extracted from the hair shaft when nuclear DNA is degraded or absent.