Exam Flashcards
Antigen
A substance that stimulates the body to produce antibodies against it
Antibodies are contained in the RBCs T/F
False
What revolutionary technique replaced blood typing for associating bloodstain evidence with a particular individual?
DNA
What are the 4 important antigens?
A, B, O, D
Agglutination is associated to what?
Incompatible blood types
What system is used currently for properly matching a donor and recipient for a transfusion?
ABO system
What percentage of blood content does plasma account for?
55
Karl Landsteiner discovered that blood can be classified by its what?
Type
What is the fluid portion of unclotted blood called?
Plasma
What kind of structure does DNA have?
Double helix
What is an example of the best current presumptive search technique that results in chemiluminescence which can last for several minutes?
Bluestar
Mitochondrial DNA is found outside the nucleus of the cell and is inherited solely from the father T/F
False
DNA is a molecule that is formed by linking together a series of repeating units known as what?
Nucleotides
Complimentary base pairing refers to what?
G always pairs with C and T always pairs with A
G always pairs with C and T always pairs with A is a fact that refers to what?
Complimentary base pairing
When is a P30 test performed?
When no sperm are found to be present within the sample
What is the building block for the human body?
DNA
Each nucleus of a cell contains how many chromosomes?
46
No two people have the same DNA T/F
False - identical twins have the same DNA
Where can a reference sample of mtDNA be obtained?
From any maternally related relative
During a sexual assault, for example, biological evidence such as hair, skin cells, semen, or blood can be left on a victim’s body or other parts of the crime scene T/F
True
Mitochondrial DNA is found inside the nucleus of the cell and is inherited solely from the mother T/F
False
Where is mtDNA found and inherited from?
Found in the mitochondria of every cell (not in the nucleus!) and inherited solely from the mother
How many nucleus vs mitochondria in each cell?
Only one nucleus but hundreds of thousands of mitochondria
Who may elimination samples be taken from?
Anyone who had lawful access to the crime scene and may have left biological material
All individuals of the same maternal lineage are what by mtDNA analysis?
Indistinguishable
Crime scene DNA samples are compared to suspect’s DNA for the presence of what?
A set of specific DNA markers
What do elimination samples help to do?
Determine if the evidence is from a suspect or another person
If multiple swabs are collected, they all should be packaged and sealed in the same container to avoid cross contamination. T/F
False
What should you do if the stained object is transportable?
Submit the item intact
In crimes of violence, how is blood usually found?
In the form of dried stains
The exact location of blood samples and controls are calculated by triangulating transient objects T/F
False
In addition to identification and comparison testing, what else may provide information concerning how blood was deposited?
The shape and pattern of the blood staining
Collection of suspected dry blood stains requires the swab to be preferably moistened with distilled water T/F
True
What should be collected as a control for bloodstains?
An unstained area adjacent to the suspected bloodstain
What is used to collect liquid blood?
A dry sterile swab
After collecting a suspected dry blood stain, it is not necessary to air dry since it was a dried stain T/F
False - the swab was moistened so it needs to be dried
What kind of container is wet swabbed blood packaged in?
Porous
Using an alternate light source (ALS) to detect semen at a crime scene is foolproof as a confirmatory test T/F
False
In a rape case, investigators can collect and analyze DNA of any consensual sexual partner from only the past day T/F
False
The crime scene investigator need not attempt to recover articles associated to a sexual assault crime scene since the victim will be examined by a medical professional to recover sufficient DNA to identify the perpetrator T/F
False
Another confirmatory test is known as a P30 test. This test is performed for the presence of spermatozoa T/F
False
What is the ideal way to preserve biological evidence?
Freeze it
Evidence with dried biological stains should be stored in a room without temperature control T/F
False
Saliva stains are not usually evident from a visual examination. However, certain types of evidence frequently contain traces of saliva such as what?
Bite marks
Where are confirmatory tests for semen done?
Can only be done in the lab
In all cases, it is essential to have the victim examined by a medical professional as soon as possible T/F
True
What other substances with fluoresce similar to semen?
Fabric softeners, toothpaste, sweat
What does BPA stand for?
Bloodstain pattern analysis
What is bloodstain pattern analysis?
The science of examining and interpreting blood present at a bloodshed event in order to determine what events occurred, in what order, and who possibly left the stains
In what shape does blood fall?
Sphere
How do bloodstains dry?
From the outside towards the inside
What end of an elongated bloodstain will typically point in the direction of travel?
Tail/narrow/tapered
Where does the tail/narrow/tapered end of an elongated bloodstain typically point?
In the direction of travel
The more viscous a fluid, what?
The slower is flows
Should you include the tail when measuring the length of a bloodstain?
No
What does it mean if a resulting bloodstain is circular?
The blood impacted the surface at 90 degrees
If an investigator were to draw an imaginary line through the long axis of bloodstains in the opposite of observed travel, they would arrive at the point in which the event occurred. This point is known as the what?
Area of convergence
In a crime scene, the direction that blood travelled, determined by the bloodstain’s shape is known as what?
Directionality
What is directionality?
The direction that blood travelled
What will allow the crime scene investigator to determine the direction from which the blood originated?
Careful analysis of bloodstain shapes, characteristics, and patterns
What is the fluid part of blood?
Plasma
What is suspended in plasma?
RBCs, WBCs, platelets
What do the fibre solids in blood do?
Help clot
What is serum?
The yellow liquid that separates a scab from the blood. This is where we find the antibodies.
What are antigens?
Structures on the RBCs that dictate the blood type
B antigen dictates what blood type?
B
Explain the relationship between antigens and antibodies
With each antigen, the body creates antibodies to protect from enemy blood, by causing clotting to trap them
What is D antigen for?
Rh factor (+ or -)
What about luminol?
Fuck luminol, we use Bluestar
What is used as a presumptive test for blood in the field?
Bluestar
What are RBCs called?
Erythrocytes
What are WBCs called?
Leukocytes
Where are antigens located?
On the surface of RBCs
What are antigens responsible for?
Blood type characteristics
What are the most important blood antigen systems?
ABO and Rh
A antigen dictates what blood type?
A
What antigen does someone have if they have O type blood?
Neither A or B
What antigen does someone have if they have AB type blood?
Both A and B
Anti B can be found in which blood type?
A
Anti A can be found in which blood type?
B
Which antis are found in AB blood?
None
Which antis are found in O blood?
Both A and B
Which antigen does Rh+ have
D
What does it mean if someone does not have D antigen?
Rh-
How much of the DNA do we need to look at?
Only a part, then it repeats
How many pairs of chromosomes in a nucleus?
23
How can DNA be used in forensics?
To both convict and exonerate, can place a suspect at the crime scene
What does CODIS stand for?
Combined DNA Index System
What is CODIS?
An electronic database of DNA profiles administered throughout the FBI
What categories of persons are entered into CODIS?
Convicted offender, arrestee, forensic, missing, unidentified, biological relatives of missing persons
Where is DNA vs mtDNA found?
DNA is found in the nucleus, mtDNA is found in mitochondria
When does DNA evidence need to be collected?
Any time it may be present and ASAP
How much blood should you obtain when swabbing a sample?
As much as you can get on the swab
Can swabs from the same sample be packaged together?
Yes
What needs to be done to collect a dry blood sample?
Wet the swab with 1-2 drops of distilled water, let it dry before packaging
How is wet blood collected?
With a dry swab, let the blood dry before packaging
How should you dry a wet blood swab?
Air dry
What kind of packaging should be used for biological materials?
Porous
When should observations about blood stains be made?
Before taking samples
How can you tell the difference between wet and dry blood?
Wet blood is shiny and dry blood is dull
How should a blood swab sample be packaged?
In a tube, in a sealed swab box, and then the box is packaged
Why do porous packaging materials need to be used in biological samples?
To prevent bacteria and mold growth that will destroy the sample
What should you do if you do not have distilled water to take a sample?
Use what you have but make a note and provide a control sample of the water you used
Where are presumptive vs confirmatory tests done?
Presumptive at scene, confirmatory in lab
How can you see semen fluoresce?
With an alternate light source due to the acid phosphatase and amylase
How can you see blood fluoresce?
Bluestar
What are the two presumptive tests for semen?
Christmas tree stain for spermatozoa and p30 test for fluid
What are we testing bite marks for?
Cells for DNA, saliva (not really though)
What is the time frame for DNA collection in SA cases?
4 days, ASAP though
Who do we need elimination samples for in a SA case?
Consensual partners
Who collects evidence in a SA case? How?
Hospital staff, with a SA kit
How should a used condom be stored?
In the freezer (because you can’t air dry it)
How can DNA be obtained from a known SA suspect?
With a DNA warrant or doctor DNA swab of the penis (within 2 days without a shower)
What are satellite stains?
Little splatter stains surrounding a large central ones
Area of Convergence
2D, measured through the centre of the bloodstain through the tail of each satellite stain, where these lines meet
Point of Origin
3D, using lines from point of origin direction as well as angle calculation, approximate location of the blood source when it was impacted
How is angle of impact calculated?
width/length, look at sin table
Why does blood fall in a spheroid configuration?
Viscosity - the blood molecules are attracted to one another and want to stick together
What are the 3 primary things to observe when investigating bloodstains?
Size, shape, and distribution of the bloodstains
Directionality
The direction that blood was travelling
What way does the tail of an elongated bloodstain point?
In the direction of travel
Effect of height on bloodstain size
Bloodstains progressively get bigger as height increases (until 7 feet)
Terminal velocity
When the force of air resistance equals the force of gravity. Bloodstains will no longer get bigger with height. Reached at 7 feet.
Passive bloodstains
Clots, drips, flows, blood pools. Aftermath of the violence
Drip Patterns
Result from blood dripping into blood, generally satellite staining
Size of satellite stains
Decrease in size as distance from blood pool increases
What does the presence of clots within a bloodstain pattern indicate?
That some time elapsed between the event that resulted in bloodshed and clot formation
When does pooling occur?
When gravitational forces pull blood to the lowest level possible and an accumulation of blood develops
Where is a transfer pattern heaviest?
In the portion that was deposited first
Swipe
When a bloodied surface rubs across a non-bloodied one
Wipe
When a non-bloodied surface rubs across a bloodied surface
When does pattern transfer happen?
When an object wet with blood comes into contact with a secondary surface
How are projected patterns produced?
By blood released under pressure
Cast off patterns
Created when blood is thrown from a blood-bearing object in motion
How can cast-off patterns be used
To estimate the minimum number of blows
Blood Spatter
A random distribution of bloodstains that vary in size and may be produced by a variety of mechanisms, varies considerably
Arterial Spurt
When blood is projected from a breached artery
What pattern is sometimes seen in arterial spurts?
V shape
Expirated patterns
Created when blood is blown out of the mouth or nose
Impact Patterns
Created by a force that results in the random distribution of smaller drops of blood
What are the 3 types of impact patterns?
Low velocity, medium velocity, high velocity
Skeletonized stain
When the centre part of a dried bloodstain flakes away or the centre part of a partially dry bloodstain is wiped away, leaving the dried outer rim
When does blood break into smaller droplets?
Only when something disrupts the surface tension
Acid phosphatase colour test
To locate and characterize a seminal stain. Acid phosphatase in semen turns purple.
Christmas Tree Stain
Stains head of spermatozoa red and tail green. No colour change if no spermatozoa in the semen
Semen vs spermatazoa
Semen is the transfer medium for spermatazoa
Where is p30 protein found?
In seminal plasma
Flow Patterns
Generally observed when volumes of liquid blood move freely along a downward path due to gravity or movement of the surface
Void Pattern
Area where no blood is found, usually a result of an individual or item between the area of impact and surroundings blocking spatter patterns
Fly and insect spots will not be present at a bloodletting scene T/F
False - there is activity of flies within a crime scene
It may be possible to detect the victim’s DNA on the male’s underwear or on a penile swab of the suspect within what time frame of the assault?
24 hours
