Blood and DNA profiling
High-velocity spatters
usually caused by gunshot wounds, although they can be caused by other weapons if the assailant exerts an extreme amount of force. They travel more than 100 feet per second and usually look like a fine spray of tiny droplets, less than one millimeter in diameter. Bullet wounds are unique because they can have both back and front spatters, or just back spatters. This depends on whether the bullet stopped after entering the victim's body or traveled through it.
Cohesion
where molecules of the same substance are attracted to one another.
Surface Tension
where molecules on the top layer of a liquid do not want to separate from one another, causing them to form a "false skin" on the surface of the liquid.
four phases of impact when a drop of blood strikes a surface:
CONTACT AND COLLAPSE - Blood droplet flattens on impact. DISPLACEMENT - Blood droplet spreads out. DISPERSION - Some particles fly off main drop at edges. RETRACTION - Particles not completely separated suck back into main drop due to adhesive forces
Increase VELOCITY also creates:
Increased SPIKES, Increased SATELITES.
an individual blood droplet can give an investigator the following useful information:
The droplet's speed at time of impact, The direction of the droplet's travel, The approximate size of a blood drop.
blood spatters can indicate important information such as:
Type and velocity of weapon, Number of blows, Handedness of assailant, Position and movements of the victim and assailant during and after the attack, Which wounds were inflicted first, Type of injuries, How long ago the crime was committed, Whether death was immediate or delayed.
What can B lymphocytes (B cells) do?
- recognize foreign proteins -divide and produce two types of cells: plasma and memory cells
Round Drops
-a blood droplet that struck a surface straight-on (at a 90º angle from the surface) -Straight-on impacts on hard, smooth surfaces produce round droplets with smooth edges. -Higher velocities and rougher surfaces produce drops with more ragged edges.
Elongated Drops
-droplets that fall on surfaces at an angle that is greater than 90º have elongated shapes. -The larger the angle, the more elliptical the droplet.
what do enzymes and proteins contain?
-phosphoglucomutase (PGM) - adenylate Kinase (AK) - Adenosine deaminase (ADA) - esterase D (EsD) - Glucose-6-phosphate dehydrogenase - polymorphic proteins
What percentage of the population are NN
22%
what is the percentage of people on the earth that have type AB blood?
3%
What percentage of the population are MM?
30%
what is the percentage of people on the earth that have type A blood?
42%
what is the percentage of people on the earth that have type O blood?
43%
What percentage of the population are MN
48%
What is the percentage of people on the earth that have Rh proteins on their RBC's?
85%
What are the 4 blood types?
A B AB O
What type of antigens does type A have?
A antigens
DNA profiling
AKA DNA fingerprinting -widely used by such programs as the innocence project to help free inmates who have been falsely convicted of crimes
what happened in 1982?
Alec Jeffreys used Leukocytes as a source of DNA to produce the first DNA profile
what happened in1940?
Alexander Seiner, working with rhesus monkeys, noticed another type of proteins on the RBC's -proteins were named Rh factor
What type of antigens does type B have?
B antigens
Bigger drop =
Bigger SPATTER
What samples are used to identify someone through DNA?
Blood samples
What type of antigens does type AB have?
Both A and B antigens
projected blood.
If they're close to the skin, the victim bleeds faster and blood can spurt from wounds as his or her heart continues to pump. This results in a larger amount of blood and a very distinctive pattern.
two aspects of determining information about blood spatters
Size and the force of impact
blood gets longer and develops a "tail."
This tail points in the direction that the drop traveled, but its length isn't part of the measurements.
Antibody structure
Y-shaped protein molecules that bind to the molecular shape of an antigen
medium-velocity spatter
a force of anywhere from 5 to 100 feet per second, and its diameter is usually no more than four millimeters. This type of spatter can be caused by a blunt object, such as a bat or an intense beating with a fist. It can also result from a stabbing
polymorphic proteins
a group-specific components (Gc) and haptoglobin (Hp)
"The Blooding" by Joseph Wambaugh
a novel that described the first legal case involving DNA evidence
As a drop falls through the air it...
accelerates until it reaches a constant or terminal velocity
Increasing velocity of the drop also causes...
an Increase in the diameter of the spatter in passive drops of blood
What do the tips of the Y-shaped antibodies attach too?
an antigen on a different red blood cell
computing the angle of the blood using this formula:
angle of impact = arcsin (opposite side/hypotenuse) = Width ÷ Length of Spatter Measure the length and width of the splatter. Divide the width of the splatter by its length. Determine the arcsin of that number, typically using a calculator with an arcsin function.
Antigen
antibody response
The technique of "stringing"
attaching strings to each spatter to see where they converge -- is just one way to determine the area of convergence, or source of the blood.
How were earlier transfusions done?
between animals and humans with varying results
What can blood typing be used for?
can be used to link a suspect to a crime scene or to exclude a suspect, but does not prove guilt
stippling
caused by a gunshot occurring at close range which results in burns on his skin from gunpowder
internal muzzle staining.
caused by a gunshot occurring at close range, which are caused when the victim's blood is sucked back into the gun's muzzle by the cooling of the explosive gases that are released when a short is fired.
What is blood typing an example of?
class evidence
what can blood spatters and clotting show?
clotting - it can indicate that multiple blows or gunshots occurred over a period of time. spatters - Blood spatters can also contain bits of tissue and bone.
what happens when antibodies attach to foreign particles?
clumping (angulation) occurs
agglutination
death is caused by incompatible blood clumping the cells
Why was death common in early blood transfusions?
death is caused by incompatible blood clumping the cells (agglutination)
What determines how fast blood dries?
depends on the surface where the blood landed, how much blood is contained in the spatter, and the heat and humidity in the crime scene. -The outer edges dry first
Karl Landsteiner
discovered that people did not have the same blood and later described A and B proteins found on the surface of the RCBs
Passive drops
drops that fall on their own due to the force of gravity on the source of the blood. -Passive drop increases velocity as it falls due to effects of gravity.
voids
empty places in the spatters that indicate that something (or someone) caught the spatter instead of the surrounding surfaces
What is found in the blood that can be used for identification purposes?
enzymes and proteins
A really dry blood spatter can skeletonize, which means...
flaking off and leaving a ring around the original diameter of the spatter
Droplet reaches TERMINAL VELOCITY due to...
friction
Velocity increases when drops fall from...
greater heights, however, patter will not become larger at heights above 7 feet
MM protien
inheriting a gene for the M protein from each parent
how is the type given to a blood sample?
is given by the presence or absence of A and B proteins on the surface of the erythrocytes
Where is the binding site of the Y-shaped protein molecule?
located at the top of the Y-shaped molecule
passive spatters.
low-velocity spatters can also result from pools of blood around the body of a victim and transfers. It can occur with some injuries, such as bleeding sustained from a punch.
plasma cells
make and secrete specific antibodies
What was blood analysis the major method of?
narrowing the suspect pool due to probabilities
People that do not have the Rh protein have a...
negative blood type
What type of antigens does type O have?
none
People that have the Rh protein has a....
positive blood type
What proteins may erythrocytes have?
protiens M and N
memory cells
remember the foreign antigen so that they can respond more rapidly if it is fond again
level line
shows how the spatter is oriented in relation to the floor and ceiling.
Why were early transfusions have a 50% chance of working on patients?
sometimes it helped or killed the person getting the transfusion because doctors were not aware that people have different blood types
Blood travels in spherical drops due to...
surface tension
The shape of a blood drop can indicate...
the distance from which the blood fell and the angle of its impact
What do you do to determine the probability of two events occurring at the same time?
the individual probabilities are multiplied
What do we do by testing more blood type proteins?
the probability for uniqueness increases and the number of other people with the same combination as the suspect decreases
low-velocity spatter
the result of dripping blood. The force of impact is five feet per second or less, and the size of the droplets is somewhere between four and eight millimeters (0.16 to 0.31 inches). This type of blood spatter often occurs after a victim initially sustains an injury, not during the infliction of the injury itself
Blood molecules are very cohesive, which means that...
they are attracted to each other, so they squeeze against each other until they form a shape with the smallest area possible.
