Hair Analysis in Forensics Study Notes

DNA Detection Requirements:
- DNA can only be detected if hair contains the hair follicle.
Class Evidence:
- Hair is considered class evidence. Cases cannot be solely solved using hair analysis unless DNA analysis is performed.
- Most hair evidence does NOT contain hair follicles.
- Forensic scientists can observe macroscopic and microscopic features of hair to narrow it down to a class of suspects (e.g., "This hair likely belongs to an Asian human").
Individual Evidence:
- Hair can be classified as individual evidence if the hair follicle is attached, allowing for DNA analysis.

Collection from Crime Scenes:
- Plucking: Removing hair directly from the scalp or skin.
- Shaking: Shaking out hair from clothing or objects.
- Scraping: Scraping surfaces to collect hair.
Collection from Victims/Suspects:
- Up to 50 hairs are collected from each body region to allow for comparison.
- Hair varies based on its location on the body, which provides a comparative baseline and compensates for inconsistencies.

Macroscopic Analysis:
- Evaluates length, color, and curliness of hair.
Microscopic Analysis:
- Analyzes the pattern of the medulla, pigmentation of the cortex, and types of scales on the cuticle.
Comparison Microscope:
- Allows scientists to view two hair samples simultaneously; considered the best way to examine hairs.

Exploring the factors that contribute to hair curliness requires understanding its physical structure.

All hair has the same basic structure consisting of:
- Follicle: The root structure embedded in the skin.
- Shaft: The visible part of hair outside the skin.

Hair consists of 3 layers:
- Cuticle (outer layer)
- Cortex (middle layer)
- Medulla (inner core)

The cuticle is a transparent outer layer made of overlapping scales that extend from the scalp to the tip of the hair shaft.
- Function: Protects the inner layers of the shaft.
- Youngest Part: The portion closest to the scalp can reveal the presence of toxins, drugs, or heavy metals through chemical tests.
Variations in Cuticle:
- Variation exists in scale shape, thickness, and pigmentation.
Examples of different scale types include:
- Coronal Scales, Imbricate Scales, Simple Serrate, Dentate, Ovate, Acuminate, Elongate, Crenate, Flattened.

Hair physical characteristics provide insight into its bodily origin:
- Pubic Hair: Exhibits buckling.
- Limb Hair (arms/legs): Typically has blunt, frayed ends.
- Beard Hair: Notable for a double medulla.

The medulla is the central part of the hair shaft and is difficult to see with low-quality microscopes.
Classifications: There are four classifications of medulla based on:
- Presence (absent, continuous, interrupted, fragmental).
- Variations in thickness, continuity, and opacity.

Definition: The Medullary Index (MI) is calculated using the formula:
$MI = \frac{\text{width of medulla}}{\text{width of cortex}}$
Interpretation of MI Values:
- MI > 0.5 indicates animal hair.
- MI < 0.33 indicates human hair.
- Examples:
- Scalp Hair: MI = 0.1
- Cow Hair: MI = 0.62
- Mustache Hair: MI = 0.25
The ratios vary for different types of animal hair as per the examples provided.

DNA can be extracted from the follicle and amplified using the Polymerase Chain Reaction (PCR).
Automated processes are used for DNA profiling.
Mitochondrial DNA (mtDNA): Can establish genetic relationships through maternal lineage. Suspects can be excluded if their mtDNA does not match the mtDNA found at the crime scene.