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Forensic Biology > Hair and Fibers > Flashcards

Hair and Fibers Flashcards

1
Q

fiber definition

A

the smallest unit of a textile material that has a length many times greater than its diameter

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2
Q

how do fibers occur?

A
  • naturally as plant and animal fibers
  • synthetic, man-made
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3
Q

hairs and fibers - evidence types

A
  • biological &/or physical
  • indirect
  • trace evidence
  • class
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4
Q

4 categories of fibers

A
  • animal fiber
  • vegetable fiber
  • mineral fiber
  • man made fiber
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5
Q

animal fiber

A

wool is most common, but only 1% of textile fibers

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6
Q

vegetable fiber

A
  • 24% of all textile fibers
  • cotton is most common
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7
Q

mineral fiber

A
  • rare
  • only asbestos
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8
Q

man made (synthetic) fibers

A

75% of all textile fibers

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9
Q

characteristics of synthetic/man made fibers

A
  • uniform
  • variety of shapes
  • absence of features
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10
Q

characteristics of animal & vegetable fibers

A
  • irregular only
  • circular to oblong
  • visible features (cuticle & medulla)
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11
Q

what do fiber analysts compare?

A
  • shape
  • dye content
  • size
  • chemical composition
  • microscopic appearences
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12
Q

fiber association

A
  • fibers from two separate places can be associated via comparison, that does not mean they derive from the same source
  • there is no fiber database that provides a probability of origin
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13
Q

Fiber Population Studies

A

relative frequencies of fiber type/color (generic) on particular surfaces

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14
Q

Color Block Studies

A

ability of a specific protocol to discriminate between similar fibers (type/color)

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15
Q

Target Fiber Studies

A

probability of finding significant numbers of a specific fiber type by random chance

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16
Q

direct transfer of fibers

A

fibers may be transferred from a victim to a suspect

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17
Q

example of direct transfer of fibers

A

fibers from victims sweater found on suspect

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18
Q

secondary transfer of fibers

A

fibers are picked up by victim and then transferred to suspect

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19
Q

example of secondary transfer of fibers

A

victim picks up fibers from his/her couch earlier in day & then transfers to the suspect later

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20
Q

how is primary vs secondary transfer determined?

A

can be determined if the order of events is known

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21
Q

what kind of timing is essential for fiber collection?

A

early collection

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22
Q

why is it essential that fibers are collected early?

A

within 24 hours an estimated 95% of all fibers may have fallen off a victim or been lost from a crime scene

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23
Q

which fibers at the crime scene are investigated?

A

only fibers not expected to be found at a crime scene are investigated

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24
Q

textile shedding

A

the most common form of fiber transfer to be encountered is the shedding from a textile

25
Q

textile (fabric)

A

a flexible, flat material made by interlacing yarns

26
Q

examples of textiles

A
  • clothing
  • carpets
  • upholstery
27
Q

which is the smallest: fiber, yarn, textile

A

fiber

28
Q

which is the biggest: fiber, yarn, textile

A

textile

29
Q

5 major types of weave patterns

A
  • plain
  • basket
  • satin
  • twill
  • leno
30
Q

what determines the weave pattern?

A

warp and weft

31
Q

warp

A

length wise fiber

32
Q

weft

A

crosswise fiber

33
Q

plain weave pattern

A
  • alternating warp & weft pattern
  • single fibers
34
Q

basket weave pattern

A
  • alternating warp & weft pattern
  • double fibers
35
Q

satin weave pattern

A

weft goes over 3 or more warps

36
Q

leno weave pattern

A

adjacent weft threads cross over each other

37
Q

twill weave pattern

A
  • weft goes over two then under two warps
  • warp goes over two then under two wefts
38
Q

thread count

A

threads per inch

39
Q

high thread count =

A

higher price

40
Q

what kind of fiber analyzing techniques are prioritized?

A

non-destructive techniques

41
Q

dyes can be analyzed with Thin Layer Chromatography (TLC)

A

dye components are separated by their differential migration caused by a mobile phase flowing through a porous, absorptive medium

42
Q

what are the variations of hair?

A
  • color
  • length
  • diameter
  • body distribution
43
Q

how are hair variations influenced?

A

influenced by ancestral affinity and age

44
Q

3 main parts of hair

A
  • cuticle
  • cortex
  • medulla
45
Q

cuticle

A

outside transparent covering

46
Q

cortex

A
  • 2nd layer made of keratin & embedded with melanin
  • contains air sacs called cortical fusi
  • gives hair color, form, and shape
47
Q

medulla

A
  • innermost layer running down the center of the cortex
  • gives hair its flexibility & offers insulation
48
Q

advantages to hair toxicology

A
  • easy to collect and store
  • externally available
  • can provide info on the individuals history of drug use or evidence of poisoning
49
Q

animal cuticle types

A
  • coronal
  • spinous
50
Q

human cuticle type

A

imbricate

51
Q

medulla types

A
  • fragmentary
  • interrupted
  • continuous
  • stacked
  • absent
52
Q

human medulla types

A
  • fragmentary
  • interrupted
  • continuous
53
Q

animal medulla types

A
  • continuous
  • stacked
54
Q

medullary index

A

width of medulla / width of cortex

55
Q

typical human medullary index

A

0.33 or less

56
Q

typical animal medullary index

A

0.50 or more

57
Q

collecting hairs

A

collect 30-50 hairs from each body region

58
Q

Postmortem Root Band (PMRB)

A

proteomic analysis of decedent scalp hair segments exhibiting a postmortem hair root band

Forensic Biology (17 decks)

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