SCI 114 Forensic Hair Analysis

A set of 30 flashcards covering forensic hair analysis including trace evidence, hair morphology, growth phases, collection, and laboratory comparison techniques based on SCI 114 lecture notes.

What is the definition of Trace Evidence?

Any type of evidence that is easily transferred from one surface to another via primary or secondary transfer, such as hairs, fibers, glass, soil, or paint chips.

What is the core statement of Locard’s Exchange Principle?

“Every contact leaves a trace” — representing the mutual exchange of material when two objects come into contact.

What specific protein and bond types compose hair strands?

Hair consists of long strands of keratin cross-linked with disulfide bonds.

What are the three layers of a hair strand?

The Cuticle (outer layer), Cortex (middle layer), and Medulla (inner layer).

Describe the composition and function of the Cuticle.

It is the outermost layer, rich in sulfur, protects the hair from environmental factors, and is composed of overlapping, scale-like cells.

What are the four types of scale patterns found on the Cuticle mentioned in the text?

Imbricate, mosaic, chevron, and petal.

What types of cells and internal structures are found in the Cortex?

Spindle-shaped cells, pigment granules, ovoid bodies, and cortical fusi.

What are the four types/degrees of medullation?

Continuous, discontinuous/interrupted, fragmented, and absent.

List the medullary patterns identified in microscopic analysis.

Amorphous, globular, aeriform lattice, uniserial ladder, multiserial ladder, and wide lattice.

What occurs during the Anagen phase of hair growth?

Anagen is the active growth phase.

What is the Catagen phase of hair growth?

It is the transitional phase between the anagen and telogen phases.

How is the Telogen phase characterized?

It is the resting phase where the hair becomes a bulbous shape, falls out easily, and eventually returns to the anagen phase.

What are the four methods listed for the collection of hair evidence?

Picking, taping, scraping, and vacuuming.

What are the requirements for collecting hair control samples from a body?

Collect $25$ pulled/cut hairs and $25$ combed hairs from various areas of the body.

In what materials should hair evidence be packaged?

A coin envelope and a druggist fold.

What range of refractive index (RI) should a mounting medium have for viewing hair with transmitted light?

A refractive index between $1.50$ and $1.60$.

What is the formula for the Medullary Index?

$$\text{Medullary Index} = \frac{\text{diameter of medulla}}{\text{diameter of hair shaft}}$$

What is the Medullary Index threshold for humans compared to animals?

Humans have an index of $1/3$ or less, while animals have an index of $1/2$ or more.

What are the characteristic features of facial hair?

A wide and even diameter, and a triangular cross-section with some shouldering.

What are the four general categories for the racial origin of head hair?

European, African, Asian, and Mixed.

What are the three possible conclusions of a common origin comparison between questioned ($Q$) and known ($K$) samples?

$Q$ and $K$ share a common origin; $Q$ and $K$ do not share a common origin; or no conclusion can be made.

What is a follicular tag and what does its presence indicate?

It is tissue from a hair follicle attached to the root; its presence indicates the hair was forcibly removed.

At what rate does human hair typically grow?

Approximately $1\,cm$ per month.

How can the approximate time of an artificial hair treatment be determined?

By measuring the length of the untreated area of the hair shaft.

What are the names of the two hair diseases/damages illustrated in the notes?

Trichorrhexis Invaginata and Trichorrhexis Nodosa.

What is the standard sample size and detection window for a hair drug test?

$100$-$120$ hairs taken near the scalp can detect repeated drug use over the last $90$ days.

Which two laboratory tests are used for hair drug detection?

ELISA is used for negative or positive results, and GC/MS is used to confirm positive results.

What is Post-Mortem Root Banding?

A hair characteristic during decomposition identified by a darkened band near the root.

What are the inheritance rules for mtDNA in hair?

mtDNA (mitochondrial DNA) is maternally inherited.

When should DNA testing be performed in relation to microscopic analysis?

DNA testing is a destructive technique and should only be performed AFTER a microscopic comparison.