Midterm Flashcards
Antigens are found on the surface of red blood cells
True
When a fluid droplet is released into the air, what shape does it typically take?
Sphere
Which of the following is not considered biological evidence?
Water
What percentage of blood content does plasma account for?
55%
A %
42%
B %
12%
AB %
3%
O %
43%
Blood typing replaced DNA for associating bloodstain evidence with a particular individual.
False. DNA replaced blood typing
Which blood types can receive O-negative blood?
All
Liquids and Gases are both fluids
True
Which of the following is not a database on the National DNA Data Bank (Canadian)?
Arrestees
The ABO blood group system classifies blood based on the presence of antigens on red blood cells.
True
Karl Landsteiner discovered that blood can be classified by its:
Group and Type
When collecting a swab of a biological substance that has dried, you should moisten the swab with phenolphthalein?
False
What are the reasons PPE should ALWAYS be worn when collecting blood or other biological fluids?
To protect yourself and your family from any potential health hazards
AND
To preserve evidence integrity
Which of the following is NOT a key characteristic of DNA?
DNA is typically single-stranded
What is the best practice when an item found at a crime scene contains potential blood or biological fluids and is transportable?
Collect the entire item
DNA Profiling is sometimes referred to as DNA fingerprinting.
True
Amylase is an enzyme produced by the prostate gland.
False
Which presumptive test can identify human blood (with a few exceptions)?
Hexagon OBTI
Which base does guanine (G) pair with in DNA?
Cytosine (C)
What should be documented when blood is located at a scene (in addition to the date and time)?
All of them
What is a limitation of using an alternate light source (ALS) in forensic investigations?
Household cleaners, fabric softeners, and soaps may fluoresce, potentially leading to false positives
TAKE PROPER PRECAUTIONS
- Protect Yourself
- Preserve Evidence Integrity
8 most common blood types
A+, A-, B+, B-, O+, O-, AB+, and AB-.
Universal donor for red blood cells
O-negative
Type ______ blood, while not universal, can be given to any Rh-positive blood type
O-positive
Database categories on United States of
America CODIS:
- Convicted offenders
- Arrestees
- Forensic index (crime scenes)
- Missing persons
- Unidentified humans
- Biological relatives of missing persons
Canada’s version of CODIS
The National DNA Data Bank (NDDB)
NDBB Database
- Convicted Offenders
- Crime Scene
- Victims
- Missing Persons
- Voluntary Donors
- Relatives of Missing Persons
- Human Remains
Liquids: molecules ________, experience attractive forces
close together
Gases: molecules _____, experience mild attractive forces
far apart
Study of forces on and in fluids
Fluid dynamics
Body Forces
- Act throughout the element.
- Tend to accelerate fluid elements.
Example of Body Forces
Weight
Normal Forces
- Act at right angles to surfaces.
- Tend to accelerate or compress fluid elements.
Example of Normal Forces
Pressure
Shear Forces
- Act parallel to surfaces.
- Tend to accelerate or deform fluid elements.
Example of Shear Forces
Viscosity
First Law (Inertia)
- An object at rest remains at rest.
- An object in motion continues in motion at constant speed and in a straight line unless acted upon by an unbalanced force.
Second Law (Force)
The acceleration of an object depends on:
- The mass of the object.
- The amount of force applied.
Third Law (Action & Reaction)
- When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
Boundary Layer
Thin fluid layer near a solid surface where
viscosity slows the flow
Droplet in Flight - Step 1
- Droplet propelled upwards.
- Kinetic energy is high.
- Kinetic energy decreases due to gravity and drag.
Droplet in Flight - Step 2
- Droplet reaches the highest point.
- Kinetic energy is at a minimum.
- Potential energy is at a maximum.
Droplet in Flight - Step 3
- Droplet falls.
- Kinetic energy increases.
- Potential energy decreases.
Surface tension and viscosity resist expansion, leading to:
Sheet → Ligament → Droplet formation.
Gunshot Spatter
- Energy is transferred to the blood via inertial force when the projectile strikes.
- Viscous force occurs as the bullet moves through the blood.
- Higher kinetic energy density results in smaller droplet size.
What is drag coefficient?
Pressure and skin friction drag
When a blood droplet is in flight, ________ refers to the resistance it encounters as it moves through the air.
Skin friction drag
The Reynolds number (Re) describes whether a fluid flow is:
– Smooth (laminar)
– Chaotic (turbulent)
Low Reynolds Number (Laminar Flow):
– The flow is smooth and ordered, like honey slowly flowing.
– Occurs when the fluid’s viscosity is greater than the forces from its movement.
High Reynolds Number (Turbulent Flow):
– The flow is chaotic and irregular, like water splashing.
– Happens when the fluid’s speed overcomes its viscosity, causing random swirls.
Droplets striking at angles other than 90° can form:
Fingers with tails
– Satellite stains
Drip Patterns:
- Satellite stains are irregular in shape and orientation.
- Directionality is not coherent (unlike impact patterns).
Low Re & We (Smooth Surfaces):
Droplet spreads until the contact line is stopped by surface tension and viscosity.
Forms a circular stain (at 90° impact).
Slightly Higher Re & We:
After maximum spread, the contact line may retract.
Moderate Re & We:
Mild splash occurs.
Fingers retract, leaving scalloped edges.
High Re & We:
Severe splashing.
Fingers remain, forming spines or breaking off to create satellite stains.
As waves travel along the sheet, they
form _____
Ligaments
More energy means a _______ surface area, which creates more droplets, but
each one will be smaller in size.
larger
Location of DNA
Nuclear DNA is housed in the nuclei of cells.
Structure of DNA
Double Helix
Four bases associated with DNA
Adenine (A), Cytosine (C), Guanine (G),
and Thymine (T)
The average human chromosome has
DNA containing _____ base pairs
100 million base pairs
Sir Alec Jeffery - Identified variable regions in DNA called “_________,” which differ between individuals.
mini-satellites
Late 1980s
DNA replaced blood typing for blood evidence analysis
Early 1990s
DNA testing became a more reliable and accurate
identification method
Minimum PPE
Mask
Gloves
Information to Document
- Size of the stain
- Shape of the stain
- Location of the stain
- Distribution of the stain(s)
Collection of Blood Evidence - Swabbing:
- Use a sterile cotton swab.
- If the sample is dry, moisten the swab with a few drops of sterile, distilled water.
- Place the swab in a drying cabinet, or use a breathable drying envelope or cardboard box.
If the sample is dry, moisten the swab with a few drops of ______
Sterile, distilled water.
Collection of Blood Evidence - Packaging:
- Package the swab in a box.
- Ensure it is properly labeled and sealed.
Humans produce ______ of saliva per day
1–1.3 liters
Amylase:
- A digestive enzyme secreted by the pancreas and salivary glands
Amylase is found in saliva at ___ higher concentrations compared to other tissues
50x
T/F: Saliva stains are typically visible to the naked eye
False
T/F: Under ALS (Alternative Light Source), saliva fluoresces at the same wavelength as semen but less brightly.
True
Presumptive tests detect _______
Amylase
Vaginal Secretions - Packaging
Package in paper evidence bags (not plastic) or a cardboard box.
An alternate light source (ALS), is also known as a
forensic light source (FLS)
Uses of ALS:
- Latent fingerprints
- Body fluids
- Hair and fibers
- Bruises
- Bite marks
- Wound patterns
- Shoe and foot imprints
- Gunshot residues
- Drug traces
Phenolphthalein Test - Solution A:
Water (moisten swab to collect sample).
Phenolphthalein Test - Solution B:
Reduced phenolphthalein (reagent).
Ethanol (increases test sensitivity).
Phenolphthalein Test - Solution C:
3% hydrogen peroxide (oxidizes phenolphthalein → phenolphthalein).
Phenolphthalein Test - Result
Immediate fuchsia-pink color change indicates a presumptive positive for blood.
Hexagon OBTI® - Human vs. Animal Blood
If human hemoglobin is present, a red line forms in the test zone (T), indicating a positive result.
Hemastix®
Hemastix uses the peroxidase method to detect blood.
Hemastix® – An immediate ______ color change indicates a presumptive positive for blood.
Dark green
Diploid
The presence of two complete sets of chromosomes in an organism’s cells.
Genome
The entire set of DNA instructions found in a cell.
Haploid
The presence of a single set of chromosomes in an organism’s cells.
Mitochondria
Circular chromosome found inside the cellular organelles.
Nucleotide
The basic building block of nucleic acids (RNA and DNA).
tRNA - Anticodon Loop
Binds to a complementary codon on messenger RNA (mRNA).
tRNA - Amino acid attachment site
Binds a specific amino acid corresponding to the anticodon.
rRNA
Forms the structural and functional core of ribosomes, responsible for protein synthesis.
rRNA ensures proper alignment of?
Ensures proper alignment of mRNA and tRNA during translation.
While each cell contains a single nucleus, it houses ________ of mtDNA, increasing the chances of successful DNA extraction
Hundreds to thousands of copies of mtDNA
Mitochondrial DNA consists of 2 strands of nucleotides called the __________ (H) strand and __________ (L) strand
Heavy, Light
mtDNA forms a
Closed-loop (circular)
structure
mtDNA - 37 essential genes, including:
- 13 genes for protein components of the electron transport
chain - 22 transfer RNA (tRNA) genes
- 2 ribosomal RNA (rRNA) genes
Conditions for Warrantless Action
A peace officer or a public officer designated to enforce federal or provincial law can exercise certain powers (as outlined in subsection 487(1) or 492.1(1)) without a warrant.
Exigent circumstances can occur when there is
Imminent danger requiring immediate action to prevent the loss, removal, destruction, or disappearance of evidence.
Exigent Circumstances - The need to protect evidence applies when:
- There are sufficient grounds to obtain authorization to seize the evidence.
- There are reasonable grounds to believe that there is imminent danger of evidence being lost or destroyed if it is not seized promptly.
- The delay in obtaining authorization would pose a serious risk to the ability to preserve evidence.
Exigent Circumstances - No warrant
If the conditions for obtaining a warrant exist, but it would be impractical to obtain one due to urgent circumstances, the officer can act without a warrant.
A peace officer or public officer (designated to enforce federal or provincial law) can seize items without a warrant if:
The officer is lawfully present in a place (with a warrant or in the course of their duties).
Seizure Criteria:
The officer believes on reasonable grounds that the item:
(a) Has been obtained through the commission of an offence.
(b) Has been used in the commission of an offence.
(c) Will provide evidence related to an offence.
T/F: Items may be moved within the scene or seized and secured in another location to prevent loss of evidence.
True
Forensic Evidence
Any physical item which may yield information which may be of used to advance an investigation or be used within court process
Steps for Evidence Collection:
- Take overall photos as found and capture bloodstain patterns.
- Conduct a visual search using bright white light.
- Perform a forensic light/laser search.
- Swab any stains for analysis.
- Collect impression evidence (fingerprints, footwear, etc.).
Evidence Types:
- Blood and other body fluids.
- Fingerprints (e.g., doorknobs, floor).
- Footwear impressions (e.g., floor, door).
Search Process - Start every search with a visual “BWL” exam. BWL stands for?
BWL = Bright White Light.
T/F: You should always consult with the attending coroner or pathologist before swabbing the body for evidence.
True
Evidence on Body - Clothing:
- Overall photos as found
- Visual / bright white light search
- Forensic light / laser / IR search
- Collect hairs, fibres, swab stains
- Consider removing clothing prior to
transport
T/F: Body removal does not require supervision or direction
False
T/F:Hands should never be bagged before packaging or transporting a body
False
The ________ permits the movement or seizure of items at a scene without a warrant to prevent loss or destruction of evidence.
Criminal Code
A _______ improves the speed of evidence examination and the flow of information from the scene to the investigator.
concurrent investigative workflow
T/F: Always consult with the Coroner before collecting or removing items from the body, but not the Pathologist.
False - Coroner or Pathologist
