Forensic Biology Flashcards
What is the Forensic Biology unit responsible for?
- analyzing biological material (blood, semen, hair, tissue, saliva)
- locating, isolating, and recovering forensic evidence
- handle sexual and physical assaults, homicides
What can hair analysis tell us?
- if hair was shed or pulled
- if it’s human or animal
- where on the body it is from
What is the growth cycle of hair?
- Anagen (active growth)
- forcible removal will include follicle tag = DNA
- lasts several years - Catagen (growth slows)
- lasts a few weeks
- root bulb shrinks and is pushed out of follicle - Telogen (shed)
- lasts a few months
- root changes shapes and hair sheds
What is hair composed of?
- cuticle
- keratinized outside covering resists chemical decomposition
- made of overlapping scales
- scale pattern determines species - cortex
- middle, pigmented section - medulla
- central canal
- medullary index
- shape and pattern used to ID species/ancestry
How can human hair be distinguished from animal hair?
- morphological microscopic examination of scale patterns
- class evidence can corroborate or exclude
Distinguishing features of body hairs (pubic, beard, scalp)
- pubic: hairs are buckled or twisted
- beard: hair is triangular in cross-section
- scalp: root is round/oval in cross-section
Distinguishing hair features between ancestries
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
How can you distinguish between shed or pulled hair?
- pulled hair detaches from scalp causing hematoma
How is a hair comparison conducted?
- need sample from suspect and victim
- 80-100 pulled scalp hairs
- 30-50 pulled pubic hairs
(pulled from all over the region)
What conclusions can be made from a hair examination?
positive: consistent with donor or coincidental match
negative: not consistent with donor or sample contained too few hairs
Class and individual evidence for hair
Class: - exclude, consistent with, or corroborates (DOES NOT ID) - hair shaft has mtDNA Individual: - DNA in follicular tag
What is a main concern with hair evidence?
- usually results in faulty evidence and the value of this evidence is overstated
What 3 factors have been added to hair research?
- hair banding (unique to decomposition and never found in the living)
- proteins (distinct genetic variation between proteins)
- stable isotope analysis (chemical fingerprints pin a specific location)
What is a Forensic Nurse responsible for?
- recovering evidence
- examining trauma
- assist in death investigation
- deal with victims of violence
- collect physical evidence compassionately
How is a sexual assault kit administered?
- 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
Collection of sexual assault evidence
- 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)
What does a presumptive and confirmatory test tell us?
Presumptive: - MIGHT be the suspected substance or is NOT suspected substance - False positives possible Confirmatory: - Definitely is suspected substance - no false positives
How is blood evidence collected?
- 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
What if blood evidence is not visible?
- conduct presumptive colour tests with different light sources and chemical substances
What are the 4 presumptive tests for blood?
- Kastle Meyer - bright pink
- Haemastix - green (interferes with DNA extraction)
- Luminol - glows blue (complete darkness required)
- Bluestar - glows blue (complete darkness not required)
What confirmatory test is used for blood?
- haemochromagen tests confirms blood
- no false positives
- cannot distinguish between human or animal blood
How do we test for human blood?
- precipitin test
What is a presumptive test for semen and how is it conducted?
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
What can give false positives for a presumptive test of semen?
- fruit juices, fungi, contraceptive creams
After a presumptive test for semen is performed with positive results, how is a confirmatory test done?
- 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
What can cause a false positive for confirmatory tests for semen?
- breast milk, amniotic fluid, female urine, vaginal fluids
How can you individualize a male?
- there is DNA in sperm and epithelial cells
- samples needed from consensual partner for elimination
In what scenario can there be an absence of semen in a sexual assault case?
- 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
What time factors need to be considered for vaginal, oral, rectal, and anal samples?
vaginal: - motile sperm = 8hrs - non-motile sperm = 16hrs - sperm heads = 48hrs oral: - up to 6hrs anal and rectal: - up to 20hrs
