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BIO315 > LECTURE 2: FORENSIC BIOLOGY > Flashcards

LECTURE 2: FORENSIC BIOLOGY Flashcards

1
Q

Biology of a crime scene

A

A huge part of the evidence identified at a crime scene is biological by nature
- Touch contact
o Fingerprints- sebaceous and eccrine secretions
o “Touch” or “trace” DNA- epithelial cells
o Sweat- Metabolites? (2021 research with ANPC)
- Blood
- Hair
- Semen
- Body Fluids
o Saliva, Faeces, Urine, Vomit
- Tissue
o Soft tissue, brain, bone, teeth

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2
Q

how many ng of DNA is required for a full profile

A

0.5ng

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3
Q

number of cells required for a full DNA prolfile

A

~76 cells

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4
Q

factors of skin cells left

A
  • Sloughing of cells
  • High vs low shedder
    o Varies day to day
  • Physiological condition
    o Eczema - more
    o Dry skin - more
    o Rough hands (manual labour) - more
  • Hand washing
  • Habits
    o Face touching, nail biting, hair
  • Contact type
    o Friction, pressure
  • Surface type
    o Rough vs smooth
  • Perspiration
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5
Q

Screening for “touches”:

A
  • Alternative light sources (ALS)
  • Fingerprint treatments
  • Common sense
  • Context/ statements
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6
Q

Blood

A
  • Complex suspension
    o Dissolved substances
    o Suspended cells and particles
  • Two important components
    o Liquid = Plasma
    o “Solid” = Cells 45%
     Erythrocytes, Leucocytes, Platelets
  • Weight: RBC > WBC > Plasma
    o Lividity
  • Where is the DNA? WBC
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7
Q

ABCs of Blood:

A
  • Appearance
    o The more blood you see, the better you can recognize it.
    o Colour, Hue, Tint, Saturation, Shine, Sheen, Reflectivity
  • Behaviour
    o Clotting
    o Separate
    o Particulates
    o Drying pattern
  • Context
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8
Q

Non-destructive processes: blood

A
  • Alternative Light Sources
    o Blood on black/red shirt (IR)
     Beams pulses of infrared light onto a surface and camera detects the infrared that is reflected back off it using filter
     Where there is blood, it is absorbed and we can see it
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9
Q

Destructive processes: blood

A
  • Presumptive Tests:
    o Phenophthalein (KM reagent) – pink colour
     Relatively specific- Oxidants x-react
     Very sensitive- 1x10E-7
     Excellent for screening (most common reagent used), low cost & good shelf life
    o Hemastix/TMB
    o Luminol
  • Confirmatory tests:
  • RSID Blood/Hematrace
    o Immunochromatograpy
    o Method of choice
    o No false positives (exc ferret)
    o Very sensitive, rapid
    o Does suffer from high dose hook effect (sample too conc.)
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10
Q

3 main structure on shaft of hair

A

the medulla, cortex and cuticle

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11
Q

Cuticle

A
  • Series of overlapping scales that form a protective covering (resistent
  • Always point to tip
  • Human scale pattern called imbricate
  • Specialised cells- keratinised
    o Species ID- Scale patterns
     SEM
     Casting
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12
Q

Cortex

A
  • Regular arrayed cortical cells
  • Impart colour
    o Embedded pigment granules
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13
Q

Medulla

A
  • Appears as central canal
  • Medullary Index
    o Medulla diameter/total
    o Humans < 1/3
  • Different person to person, origin to origin
  • Continuous, interrupted, fragmented, absent
  • Speciation based on pattern
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14
Q

where is the nuclear material of hair

A

Root

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15
Q

3 phases of hair growth

A

1) Anagen
2) Catagen
3) Telogen

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16
Q

Anagen

A

Initial growth phase, actively producing hair, best phase to get DNA

17
Q

Catagen

A

Transition phase, hit or miss to get DNA

18
Q

Telogen

A

Final phase, hair falls out, Follicular tag, the ones falling out of hair, unlikely to give profile, mitochondrial can be found there

19
Q

Semen

A
  • Exocrine secretion
    o Semen- carrier fluid
     Typical ejaculate 1.5-5mL
     Contains 40-250 million sperm cells
    o Contains Acid Phosphatase and PSA P30
20
Q

Aspermic

A

no sperm cells

21
Q

Oligospermic

A

low sperm cells

22
Q

DNA source: Semen

A

o Sperm head
o Sloughed UT lining
o Cell free DNA – just DNA free in the fluid cell

23
Q

ABCs of semen:

A
  • Appearance
    o White, crusting
    o Easily mistaken for female secretions
  • Behaviour
    o Spread liquid
  • Context
    o “Are the circumstances consistent with semen?”
24
Q

Non destructiver processes: semen

A
  • Alternative Light Sources
    o ~450nm wavelength light
     Blue light/Orange glasses
     Fluorescence due to the presence of molecules such as Flavin and Choline-conjugated proteins
     Fluorescence can also be masked by certain types of fabrics and fabric treatments
25
Q

Destructive processes: semen

A
  • Presumptive Tests
    o Acid Phosphatase test
     The male prostate gland produces and secretes the enzyme acid phosphatase into semen (AP)
     Using AP reagent the AP present in semen will produce a dark purple color in less than a minute (from colorless/slightly tinted)
     The test for AP remains highly presumptive
    • Vaginal secretions and other bodily fluids contain detectable levels
    • Should be read within 120s (some research to suggest longer)
    Confirmatory tests:
    o PSA test
     As per hematrace
     RSID Semen (also saliva)
    o Microscopy
     H&E Stain
     Christmas Tree stain
     Intact?
    o Immunohistochemistry
26
Q

Body fluids

A
  • Saliva, Faeces, Urine, Vomit
    o All have potential for cellular material
  • Saliva/Urine
    o Other opportunities such as metabolites
27
Q

Sampling for forensic biology

A

tapelifts, swabs, scraping/excising, bagging/direct collection

28
Q

Tapelifts

A
  • Adhesive tape
    o Wrapped around fingers and “dabbed” onto surface
     DNA
    o Strips on a garment
     Fibres
  • Scotch, mini-tapes, stubs
29
Q

Swabs

A
  • Range of swab types and shapes
  • Some better for various substrates
    o Cotton/Rayon- Blood
    o Foam- trace DNA
    o Flocked- ? Better at all ? yes, because the fibres make it easier to get cells on and out
  • Rubbed onto surface to transfer material to swab head
30
Q

Scraping/excising

A
  • Scraping- Using a razor blade or similar, scrape the material onto a piece of paper and transfer to a tube/storage
  • Excising- Cut out the stain of interest
    o Nothing left behind
31
Q

Bagging/Direct collection of entire exhibit

A

o Straight into package
o Benefit for multiple testing later
 Fingerprinting and Biology and fibre analysis
o Must consider that some evidence may be lost
 But retained in bag/packaging
 Obliterated fingerprints
o Must collect into the correct packaging
 9/10 = paper bag

32
Q

DNA Extraction

A
  1. Bust cells open
  2. Isolate the DNA from the cellular “soup”
  3. Purify
  4. Elute (create a liquid sample high in concentration and purity)
33
Q

PCR

A
  • Copy up the DNA to a detectable level
  • Target the regions of the DNA we’re after
    o Microsatellites/ Short Tandem Repeats (STRs)
34
Q

Capillary electrophoresis

A
  • Separate the fragments by size to determine genotype

BIO315 (4 decks)

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