forensic science serology

What is an antigen and how is it useful in individualizing blood?

An antigen is a substance, usually a protein, that stimulates the body to produce antibodies against it. It is useful to individualizing blood because it imparts specific characteristic to the blood it was taken from, meaning it is far easier to match to an individual because the evidence the blood given from the individual will either match very closely or not at all

What is an antibody, and what happens when an antibody reacts with its specific

antigen?

An antibody is a protein that destroys or inactivates a specific antigen; antibodies are found in

the blood serum. When it reacts with its specific antigen they combine and attach to a cell.

Antibodies are typically when two antigens can connect and a vast network of cross-linked

cells is seen known as agglutination.

What factor is most whole blood typed for? What is the most common blood type

in the United States? Which is least common?

The A-B-O. O is the most common and AB is the least common.

For what other application do forensic scientists often use specific antigen–

antibody reactions? What is the EMIT technique frequently used for, and what is

its greatest limitation?

To link evidence to an individual. The EMIT test is typically used to detect marjuana in urine,

but limitations include the fact that it will detect THC Metabolite making to difficult to discover if

the individual was actually smoking marijuana.

What is the difference between monoclonal and polyclonal antibodies? Which

type are more useful for the forensic scientist and wh

Monoclonal antibodies are a collection of identical antibodies that interact with a single

antigen site. Polyclonal antibodies are produced by injecting animals with a specific antigen; a

series of antibodies produced responding to a variety of different sites on the antigen.

Monoclonal antibodies are far more useful to forensic scientists because the antibodies can

react only with the specific antigen, making it more individualized

List two commonly used color tests for blood. How does a luminol test differ

from these tests?

Benzidine and Kastle-Meyer. Luminol produces light with a positive reaction, not color.

What is the purpose of a precipitin test? Name three strengths of precipitin tests.

The purpose of the precipitin test is to determine the species of blood evidence. Three

strengths include that the test is sensitive, requires a small amount of blood for testing,

and blood stains dried for years can still be tested.

What is a genotype and how do parents’ genotypes affect the blood type of their

offspring? In what area of the law does this information have important

implications?

A genotype is the particular combination of genes present in the cells of an individual, and a

person's genotype or blood type is decided by their parents. Area of the law is determining

maternity, child custody, etc.

What is acid phosphatase and how is it used by forensic scientists?

Acid Phosphatase are enzymes found in high concentration in semen. It is useful to forensic

scientists because it can identify the presence of semen.

List three reasons why spermatozoa are often not found in seminal fluid collected

at a crime scene.

An become tightly bound to cloth, becomes brittle when dry and easily disintegrates,

someone's sperm can have an abnormally low sperm count (oligospermia) or no sperm at all -

be sterile (aspermia).

Why is it important for investigators to seek information about when and if

voluntary sexual activity last occurred before a sexual assault?

To not alter or ruin the results of the rape kit test.

Discuss the information that can be gained from bloodstain pattern analysis about the

events involved in a violent crime

The direction from which blood originated

The angle at which a blood droplet struck a surface

The location or position of a victim at the time a bloody wound was infected

The movement of a bleeding individual at the crime scene

The approximate number of blows that struck a bleeding victim

The approximate location of an individual delivering blows that produced a bloodstain

patter

Can provide valuable insights into events that occurred during the commission of a

violent crime.

What are the physical properties of blood?

Surface tension “Blood has surface tension, causing it to form drops.

The size of these drops varies based on factors like

the height of the fall and the angle of impact on a

surface. This tension is what allows blood to maintain

a drop shape during its flight and makes the resulting

stain a key indicator of the force and angle involved.

Viscosity “Blood viscosity is an important determinant of local

flow characteristics, which exhibits shear thinning

behavior: it decreases exponentially with increasing

shear rates.

Specific gravity “The specific gravity (relative density) of human whole

blood and plasma from 25 healthy volunteers was

determined gravimetrically.

Projectile in motion -“Ballistics is the study of projectile motion and a critical

area of investigation in forensic study. When a

projectile is fired from a rifle or handgun, it travels at a

specific velocity. A projectile in motion can be

described by both horizontal and vertical motions.

Explain how (a) surface texture (b) directionality, and (c) angle of impact affect the shape

The surface texture can affect the shape, size, and splatter results.

The direction of travel of blood striking an object may be discerned because the

pointed end of a bloodstain always faces its direction of travel.

The angle of impact can be determined by measuring the degree of circular distortion.

At right angles the blood drop is circular; as the angle decreases, the stain becomes

elongated.

differentiate these types of bloodstains: passive

can be determined by measuring the

degree of circular distortion. At right

angles the blood drop is circular; as the

angle decreases, the stain becomes

elongated.

differentiate these types of bloodstains: transfer

Simple transfer patterns are produced

when the object makes contact with the

surface and is removed without any

movement of the object.

“the first transfer pattern will typically

contain the most complete and defined

imprint of the blood-bearing object, as it is

the initial contact with a clean surface,

while subsequent transfers will

progressively become less distinct due to

the gradual distribution and dilution of

blood on the object with each contact,

resulting in a fainter or more smeared

pattern

differentiate these types of bloodstains: projected

caused when a force greater than gravity

acts to create the blood- stain”

differentiate these types of bloodstains: void

The blank space on the surface or

object may give a clue as to the size

and shape of the missing object or

person.

differentiate these types of bloodstains: flows

Interruption of a flow pattern may

indicate the sequence and passage of

time between the flow and its

interruption.

differentiate these types of bloodstains: pools

Considering the drying time of a blood

pool can yield information about the

timing of events that accompanied the

incident.

differentiate these types of bloodstains: drip trail

The pattern may show direction and

speed of movement, lead to a

discarded weapon, or provide

identification of the suspect by his or

her own blood.

differentiate these types of bloodstains: expirated blood

The presence of bubbles of oxygen in

the drying drops or a lighter color as a

result of dilution by saliva can

differentiate a pattern created by

expirated blood. And The presence of

expirated blood gives an important clue

as to the injuries suffered and the events

that took place at a crime scene

What is the difference between the shape of a bloodstain that impacts a surface at a low

angle and one that impacts at a higher angle?

The impact angle of blood on a flat surface can be determined by measuring the

degree of circular distortion. At right angles the blood drop is circular; as the angle

decreases, the stain becomes elongated

What is the difference between forward spatter and back spatter? Which is more

likely to be deposited on the object or person creating the impact?

Forward spatter is projected outward and away from the source.

Back spatter, also known as blow-back spatter, is projected backward from the source

n general, as both the force and velocity of impact increase, what happens to the

diameter of the resulting blood droplets?

Drops with diameters of less than 1 mm from an applied force of 100 ft/sec or faster

Define the terms area of convergence and area of origin and explain what kind of

information each reveals to an investigator.

The area of convergence is the point on a two-dimensional plane from which the drops

in an impact pattern originated.

The area of origin of an impact bloodstain pattern is the area in a three-dimensional

space from which the blood was projected.

Name three factors that affect the amount of backward spatter produced by a

gunshot wound

The barrel of the gun, the location of the wound on the body, and the distance between

the victim and the gun muzzle

What is the drawback effect? How is it helpful to an investigator?

When the victim is close range of a shooter the blood will splatter back into the barrel

of the gun. It is significant in investigations because it has the DNA of the victim in the

shooter's gun.

What determines the size of blood drops in a cast-off pattern? Explain

The size and shape of the surface from which the blood is being flung.