11/25/13

Learning Goal: Understand and apply concepts in molecular biology

Warm-Up: A forensic scientist has collected hair samples from a crime scene. Predict how you believe they determine similarities and differences in the samples.

Hair EvidenceMolecular Biology Techniques

The Function and Structure of Hair

• Hair on mammals helps to regulate body temperature, decrease friction, and protect against sunlight.

• Hair consists of (a) a hair shaft produced by (b) a follicle embedded in the skin.

• A hair has three layers (illustrated above): the inner medulla, the cortex, and the outer cuticle.

Anatomy of a HairHair Shaft

Sebaceousgland Epidermis

DermisPapilla

Follicle•Hair is an appendage of the skin that grows out of a hair follicle.

Root•The length of a hair extends from the root embedded in the follicle. • A single root

contains sufficient DNA

for analysis

Cuticle

•The cuticle is the transparent outside covering of the hair.

•It is formed by overlapping scales that always point toward the tip of the hair.

Cortex•The Cortex is the thickest layer •It is the interior of the hair•It is embedded with pigment granules that give hair its color.

Pigment granules are absent in grey hairs

Medulla•a collection of cells which appears as a canal running through the center of the hair

•the medulla is the most predominant hair feature in many species

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Types of Medulla

The medulla can be hollow or filled, absent, fragmented, continuous, doubled, pigmented, or un- pigmented.

Type of Medulla?

Types of Hair

Buckled Blunt Double Medulla• Different regions of the body on which hair can vary

are (1) head, (2) eyebrows and lashes, (3) mustache and beard, (4) underarms, (5) overall body (auxiliary hair), and (6) pubic.

• The physical characteristics of hairs provide information about which part of the body they came from.

The Life Cycle of Hair

• Hair proceeds through 3 stages as it develops:

• Anagen stage - hair actively grows. The cells around the follicle deposit materials in the hair.

• Catagen stage - hair grows and changes. • Telogen stage - when the follicle becomes

dormant, hairs easily lost.

Treated Hair

• Bleaching disturbs the scales on the cuticle and removes pigment leaving hair brittle and a yellowish color.

• Dyeing colors the cuticle and the cortex of the hair shaft. • Treated hair will have unique

characteristics.

Racial Differences • Each racial group has hair with unique

physical characteristics.• These characteristics, however, will not

apply to all individuals in these groups. • Sometimes it is impossible to identify

which racial group a hair belongs to.

Medullary Index

• The percentage or fraction of the hair’s width occupied by the medulla

• [between 0 and 1]

Medullary Index?

Animal Hair and Human Hair

• Animals: Medullary Index of 0.5 or higher.

• Humans: Medullary Index of 0.33 or lower.

Animal Hair and Human Hair

• Pigmentation in animal hair is denser toward the medulla. In Humans it tends to be denser toward the cuticle.

• Unlike human hair, animal hair abruptly can change colors in banded patterns.

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Animal Hair and Human Hair • The CuticlesSpinous Coronal Imbricate

• The outermost layer of the hair shaft (the cuticle), is typically different in animals and humans. • Animals have a spinous or coronal cuticle.• Humans have an imbricate cuticle.

Using Hair in an Investigation

• Macroscopic investigation – length, color, texture.

• Microscopic investigation – Detail• Phase contrast microscopy - dyes• Electron microscopes – hair interior

Testing for Substances in the Hair Shaft • Chemicals that the skin absorbs often can be

detected by analysis of the hair shaft. • A forensic scientist can perform chemical tests

for the presence of various substances. • The hair shaft can be examined in sections to

establish a timeline for exposure to toxins. • Neutron Activation Analysis (NAA) can determine

concentrations of substances in the sample.

Testing the Hair Follicle

• Microscopic assessment of the follicle is performed first because it is cost effective and quick. • If a microscopic match is found, the follicle

can be blood tested and perhaps show the blood type.

• If a microscopic match is found, the follicle can be DNA analyzed to provide identification with a high degree of confidence.