Forensics Quiz- hair

What information can hair evidence give investigators? What kind of evidence is hair evidence?

• Information it can give: Hair color, texture, length, and microscopic characteristics; may also provide DNA if the root is present.

• Type of evidence: Trace evidence

• Evidence classification: Usually class evidence, but DNA testing can potentially make it individual evidence

Parts of the hair shaft (cuticle, medulla, cortex, pigment/melanin granules, etc.).

• Cuticle: Outer protective layer; made of overlapping scales.

• Cortex: Middle layer; contains melanin/pigment that gives hair its color.

• Medulla: Inner core; may be continuous, fragmented, or absent.

• Melanin granules: Pigment particles in the cortex that determine hair color.

• Medulla patterns found in humans (4)

• Continuous: The medulla forms one unbroken line from the root toward the tip of the hair.

• Interrupted: The medulla is present but has clear gaps along its length.

• Fragmented: The medulla appears as small, separated pieces rather than a continuous line.

• Absent: There is no visible medulla in the hair shaft.

Cuticle patterns (imbricate, coronal, spinous-what kinds of animals have these? What do humans have? What do they look like? 

• Imbricate → Humans

  • Cuticle scales overlap like shingles on a roof.

  • This is the most common human cuticle pattern.

• Coronal → Small rodents (like mice and rats)

  • Scales form crown-like rings around the hair shaft.

  • Looks like stacked crowns/cups.

• Spinous → Cats, seals, and some other animals

  • Scales have pointed, petal-like edges that stick outward.

  • Looks spiky or thorn-like.

Easy way to remember:
🧑 Humans = Imbricate → overlapping shingles
🐭 Rodents = Coronal → crowns
🐱 Cats = Spinous → spikes

Calculating a medullary index.

• Medullary Index: A ratio comparing the diameter of the medulla to the diameter of the entire hair shaft.

• Formula: Medullary Index = Medulla diameter ÷ Hair shaft diameter

• Example: If the medulla is 0.03 mm and the hair shaft is 0.09 mm:
  0.03 ÷ 0.09 = 0.33

• Forensics: Humans usually have a medullary index less than ⅓, while many animals have an index greater than ½.

• Using a medullary index to determine if a hair is from a human or animal.

• Medullary index:

  • Human hair: Usually less than ⅓

  • Animal hair: Usually greater than ½

  • Formula: Medulla diameter ÷ total hair diameter

• What are other ways we can tell a human hair apart from an animal hair?

• Other differences:

  • Medulla: Humans often have a thin, fragmented, or absent medulla; animals often have a thicker, more prominent medulla.

  • Cuticle: Humans have imbricate scales; animals may have coronal or spinous scales.

  • Pigment: Human pigment is usually more evenly distributed; animal pigment may be more concentrated or patterned.

  • Root: Human and animal hair roots can have different shapes and appearances

• Calculate how many days a hair has grown if you know the length grown.

• Human hair grows about 0.5 mm per day.

• Formula:
  Days = length grown ÷ 0.5 mm/day

• Example: If hair grew 10 mm:
  10 ÷ 0.5 = 20 days.

• Characteristics of hair to determine racial/ethnic background.

• Hair characteristics can suggest ancestry, but they cannot reliably identify a person’s race/ethnicity by themselves.

• Investigators may examine:

  • Hair shape/cross-section (round, oval, flattened)

  • Texture and thickness

  • Pigment distribution

  • Degree of curl

• Life cycle of hair (anagen, catagen, telogen-what happens in these stages?

• Anagen (Growth):

  • Hair is actively growing.

  • Root is usually soft, elongated, and club-like with tissue attached.

  • Hair is firmly attached to the follicle.

• Catagen (Transition):

  • Hair stops actively growing.

  • Follicle shrinks and the hair begins separating from its blood supply.

  • Shortest stage.

• Telogen (Rest):

  • Hair is no longer growing and rests in the follicle.

  • Eventually the hair falls out naturally.

  • Root is typically hard, dry, and club-shaped.

• We find a hair, how can we tell if it was in the anagen stage or telogen stage? 

• Anagen hair: Root has tissue attached and looks actively growing → usually has a soft, elongated appearance.

• Telogen hair: Root is club-shaped, dry, and lacks tissue → indicates the hair naturally shed.

• Easy memory: Anagen = attached & growing; Telogen = resting & shedding.

• What kind of DNA can you acquire from a hair in the anagen stage? Telogen stage? What does this mean?

• Anagen hair: Can contain nuclear DNA because the root still has living cells/tissue.

  • Nuclear DNA is highly individualizing and can potentially identify a specific person.

• Telogen hair: Usually does not contain enough nuclear DNA because the root is no longer living tissue.

  • It can still contain mitochondrial DNA (mtDNA), which is useful for determining a maternal lineage, but is less specific than nuclear DNA.

• How can we use hair to determine if a person has been poisoned with heavy metals like arsenic?

• Heavy metals such as arsenic can accumulate in hair as it grows.

• Investigators can test sections of the hair for arsenic concentrations.

• Because hair grows at a fairly predictable rate, the location of arsenic along the hair shaft can provide clues about when exposure occurred.

• This can help investigators determine whether someone was exposed to a heavy metal over time, rather than just at one specific moment.