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CRIM 355 > Forensic Biology > Flashcards

Forensic Biology Flashcards

1
Q

What is the Forensic Biology unit responsible for?

A
  • analyzing biological material (blood, semen, hair, tissue, saliva)
  • locating, isolating, and recovering forensic evidence
  • handle sexual and physical assaults, homicides
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2
Q

What can hair analysis tell us?

A
  • if hair was shed or pulled
  • if it’s human or animal
  • where on the body it is from
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3
Q

What is the growth cycle of hair?

A
  1. Anagen (active growth)
    - forcible removal will include follicle tag = DNA
    - lasts several years
  2. Catagen (growth slows)
    - lasts a few weeks
    - root bulb shrinks and is pushed out of follicle
  3. Telogen (shed)
    - lasts a few months
    - root changes shapes and hair sheds
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4
Q

What is hair composed of?

A
  1. cuticle
    - keratinized outside covering resists chemical decomposition
    - made of overlapping scales
    - scale pattern determines species
  2. cortex
    - middle, pigmented section
  3. medulla
    - central canal
    - medullary index
    - shape and pattern used to ID species/ancestry
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5
Q

How can human hair be distinguished from animal hair?

A
  • morphological microscopic examination of scale patterns

- class evidence can corroborate or exclude

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6
Q

Distinguishing features of body hairs (pubic, beard, scalp)

A
  • pubic: hairs are buckled or twisted
  • beard: hair is triangular in cross-section
  • scalp: root is round/oval in cross-section
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7
Q

Distinguishing hair features between ancestries

A

African: flat, oval in X-section, curled, dense uneven pigment
Asian: wide in X-section, coarse pigment
European: oval/round in X-section, fine to coarse pigment evenly distributed

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8
Q

How can you distinguish between shed or pulled hair?

A
  • pulled hair detaches from scalp causing hematoma
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9
Q

How is a hair comparison conducted?

A
  • need sample from suspect and victim
  • 80-100 pulled scalp hairs
  • 30-50 pulled pubic hairs
    (pulled from all over the region)
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10
Q

What conclusions can be made from a hair examination?

A

positive: consistent with donor or coincidental match
negative: not consistent with donor or sample contained too few hairs

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11
Q

Class and individual evidence for hair

A 
Class:
- exclude, consistent with, or corroborates (DOES NOT ID)
- hair shaft has mtDNA
Individual:
- DNA in follicular tag
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12
Q

What is a main concern with hair evidence?

A
  • usually results in faulty evidence and the value of this evidence is overstated
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13
Q

What 3 factors have been added to hair research?

A
  1. hair banding (unique to decomposition and never found in the living)
  2. proteins (distinct genetic variation between proteins)
  3. stable isotope analysis (chemical fingerprints pin a specific location)
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14
Q

What is a Forensic Nurse responsible for?

A
  • recovering evidence
  • examining trauma
  • assist in death investigation
  • deal with victims of violence
  • collect physical evidence compassionately
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15
Q

How is a sexual assault kit administered?

A
  • need to swab vagina, cervix, rectum, anus, mouth, and external areas
  • comb pubic hair to collect loose hairs
  • swabs must air dry to prevent mold
  • collect comparison sample of pulled hair
  • fingernail scrapings
  • clothing
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16
Q

Collection of sexual assault evidence

A
  • victim must consent
  • delay from unconscious victim may result in loss of evidence
  • comparison needed from consensual partners
  • Bill C-104 allows police to collect DNA from suspects and unconscious victims (controversial)
17
Q

What does a presumptive and confirmatory test tell us?

A 
Presumptive:
- MIGHT be the suspected substance or is NOT suspected substance
- False positives possible 
Confirmatory:
- Definitely is suspected substance 
- no false positives
18
Q

How is blood evidence collected?

A
  • if it’s on a person or object, needs to be swabbed

- objects, clothing, and weapons are to be placed in paper bags to prevent mold

19
Q

What if blood evidence is not visible?

A
  • conduct presumptive colour tests with different light sources and chemical substances
20
Q

What are the 4 presumptive tests for blood?

A
  1. Kastle Meyer - bright pink
  2. Haemastix - green (interferes with DNA extraction)
  3. Luminol - glows blue (complete darkness required)
  4. Bluestar - glows blue (complete darkness not required)
21
Q

What confirmatory test is used for blood?

A
  • haemochromagen tests confirms blood
  • no false positives
  • cannot distinguish between human or animal blood
22
Q

How do we test for human blood?

A
  • precipitin test
23
Q

What is a presumptive test for semen and how is it conducted?

A

Acid Phosphatase Test

  • detects acid phosphatase (enzyme secreted by prostate gland into seminal fluid)
  • filter paper is dampened with water and placed over suspect area
  • if acid phosphatase is present, it will transfer
  • rapid purple colouration indicates semen is present
24
Q

What can give false positives for a presumptive test of semen?

A
  • fruit juices, fungi, contraceptive creams
25
Q

After a presumptive test for semen is performed with positive results, how is a confirmatory test done?

A
  • detect spermatozoa using a microscope
  • stained material is placed in water which transfers the spermatozoa and a sample of the water can be stained and analyzed under a microscope
26
Q

What can cause a false positive for confirmatory tests for semen?

A
  • breast milk, amniotic fluid, female urine, vaginal fluids
27
Q

How can you individualize a male?

A
  • there is DNA in sperm and epithelial cells

- samples needed from consensual partner for elimination

28
Q

In what scenario can there be an absence of semen in a sexual assault case?

A
  • no ejaculation
  • condom used
  • victim washed
  • offender has disease that affects semen
  • victim has vaginal condition that destroys semen
  • poor collection
  • victim lied or was mistaken
29
Q

What time factors need to be considered for vaginal, oral, rectal, and anal samples?

A 
vaginal:
- motile sperm = 8hrs
- non-motile sperm = 16hrs
- sperm heads = 48hrs
oral:
- up to 6hrs
anal and rectal:
- up to 20hrs

CRIM 355 (11 decks)

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