Forensic Science Final

In what type of cells in the human body is an individual's genetic material (DNA) located?

in every nucleated cell in the body

What can the location, distribution, and appearance of bloodstains and spatters be useful for in a crime scene investigation?

interpreting and reconstructing the events that produced the bleeding

What three key pieces of information may bloodstain pattern interpretation uncover?

The direction of origin, the angle of impact, and the location/position of the victim when wounded

What type of bloodstain spatter occurs when an object impacts a source of blood?

Impact spatter

Spatter that is projected outward and away from a blood source is known as _____ spatter.

forward

What is another name for back spatter?

Blow-back spatter

What is the primary limitation of classifying impact spatter patterns by velocity and droplet size?

It cannot illuminate the specific events that produced the spatter pattern

Low-velocity spatter consists of drops with diameters of 4 mm or more, produced by an applied force of up to _____.

5 ft/sec

Medium-velocity spatter consists of drops with diameters from 1-4 mm, produced by an applied force of _____.

5 to 25 ft/sec

High-velocity spatter consists of drops with diameters of less than 1 mm, produced by an applied force of _____ or faster.

100 ft/sec

In general, stain size categories (low, medium, high velocity) should be used cautiously and for _____ purposes only.

descriptive

What is the area of convergence in bloodstain pattern analysis?

The point on a two-dimensional plane from which the drops in an impact pattern originated

How can the area of convergence be established from individual bloodstains?

By drawing straight lines through the long axis of several bloodstains, following the line of their tails

What is the area of origin in bloodstain pattern analysis?

The area in a three-dimensional space from which the blood was projected

What does the area of origin reveal about a crime scene?

The position of the victim or suspect in space when the stain-producing event took place

What method is commonly used at a crime scene to approximate the area of origin?

The string method

Gunshot spatter can produce fine forward spatter from an exit wound and _____ from an entrance wound.

back spatter

Under what circumstance does a gunshot produce only back spatter?

If the bullet does not exit the body

A pattern created when a blood-covered object flings blood in an arc onto a nearby surface.

cast-off pattern

What are two common ways a cast-off pattern is produced?

By a bloody fist or a weapon between delivering blows

How can one determine the minimum number of blows delivered using cast-off patterns?

By counting and pairing the forward and backward patterns

A blank space created when an object blocks the deposition of blood spatter onto a target surface

void pattern

What might a void pattern reveal to an investigator?

The size and shape of the missing object or person, or the body position of the victim or assailant

A series of drops, separate from other patterns, formed by blood dripping off an object or injury

drop trail pattern

What is the primary method for documenting bloodstain evidence at a scene?

noting, studying, and photographing each pattern and drop

Name three types of non-criminal cases where DNA analysis is used

Paternity cases, probate issues, and immigration cases

What technology has allowed forensic scientists to associate a bloodstain with a single individual?

DNA analysis

What does the acronym CODIS stand for?

Combined DNA Index System

What three types of DNA profiles are maintained in the CODIS databases?

convicted offenders, unsolved crime scene evidence, and missing persons

List four biological sources of DNA evidence

Blood, semen, saliva, skin cells (touch DNA), hair, or bone

List three common crime scene items that can be sources of DNA evidence.

Bottles, cans, glasses, cigarettes, bite marks, or envelopes

What is the approximate percentage of the population with type O blood?

43%

Which blood type has both anti-A and anti-B antibodies?

Type O

Which blood type has neither anti-A nor anti-B antibodies?

Type AB

An individual with type A blood has _____ antigens on their red blood cells.

A

An individual with type O blood has which antigens on their red blood cells?

Neither A nor B antigens

What test is used to determine if a bloodstain is of human or animal origin?

The precipitin test

How is the human antiserum used in the precipitin test typically created?

It is derived from rabbits that have been injected with the blood of a known animal (in this case, human blood)

In the gel diffusion technique for species origin, what indicates a positive result for human blood?

A line of precipitation forms where the antigens (from the bloodstain) and antibodies (from the human antiserum) meet

How should all biological evidence be stored until delivery to the laboratory?

It should be refrigerated or stored in a cool location

How should a stained article of biological evidence be packaged?

It should be packaged separately in a paper bag or a well-ventilated box

What two important physical properties are evaluated to compare glass fragments?

Density and refractive index

Cracks in glass that radiate outward from the point of impact are called _____ fractures.

radial

Cracks in glass that encircle the hole from a projectile are called _____ fractures.

cocentric

What is the principle of the flotation method for comparing glass densities?

A glass particle is immersed in a liquid to compare its density

What can be determined by analyzing the radial and concentric fracture patterns in glass?

The direction of impact

How can the sequence of successive impacts on a piece of glass be determined?

A fracture always terminates at an existing line of fracture

How should a suspect's shoes or clothing be packaged if they are to be examined for glass fragments?

They should be individually wrapped in paper

What aspect of soil do forensic geologists characterize and compare?

The mineral content of the soils

The shaft of a hair, which is subjected to the most intense forensic examination, is composed of what three layers?

The cuticle, cortex, and medulla

What translucent tissue, sometimes found surrounding a hair's shaft near the root, is a rich source of nuclear DNA?

A follicular tag

In which of the three phases of hair growth is the probability of detecting DNA in the hair root most likely?

The anagen (or early growth) phase

Besides the medulla, what other features of the cortex are important for comparing human hair?

The distribution, shape, and color intensity of the pigment granules

What two techniques are invaluable for distinguishing most paint binder formulations?

Pyrolysis gas chromatography and infrared spectrophotometry

What database do crime labs often use to identify the make and model of a car from a paint chip?

The PDQ (Paint Data Query) database

When collecting paint evidence from a hit-and-run, where must uncontaminated reference paint be collected from?

From an undamaged area of the car that is in close proximity to the damaged area

What are the four typical coatings applied to the body of an automobile by manufacturers?

Electrocoat primer, primer surfacer, basecoat, and clearcoat

The glass found in car windshields, which has a layer of plastic between two pieces of glass, is called _____ glass.

laminated

Fibers manufactured from natural raw materials, like rayon and acetate, are classified as _____ fibers.

regenerated

Fibers derived in whole from animal or plant sources are known as _____ fibers.

natural

Fibers produced solely from synthetic chemicals, like nylons and polyesters, are classified as _____ fibers.

synthetic

Synthetic fibers are composed of _____, which are large numbers of atoms arranged in repeating units known as monomers.

polymers (or macromolecules)

What is the initial step in comparing questioned and reference fibers?

Microscopic comparisons for color and diameter characteristics using a comparison microscope

What reliable method identifies the generic class of fibers by observing how their molecules selectively absorb infrared light?

Infrared spectrophotometry

What is the most widely used and successful DNA profiling procedure today?

Short tandem repeat (STR) analysis

STR testing uses a _____ process to test multiple genetic markers and determine gender simultaneously.

multiplex PCR

STR analysis focuses on short repeating sequences within DNA rather than the entire genome, as was done in the earlier _____ method.

RFLP (Restriction Fragment Length Polymorphism)

The speed of decomposition in low explosives, called _____, causes the walls of a container to fragment and fly outward.

deflagration

What type of explosives are ultra-sensitive to heat, shock, or friction and are used in blasting caps or primers?

Primary explosives

Black powder is a mixture of potassium or sodium nitrate, _____, and sulfur.

charcoal

What are the two most widely used low explosives?

Black powder and smokeless powder

Smokeless powder consists of nitrated cotton (nitrocellulose) or a combination of nitroglycerin and _____.

nitrocellulose

At a fire scene, where must the search focus to be most productive in finding an accelerant or ignition device?

The fire's origin

In a fire investigation, what is the probable origin of the fire likely to be?

The lowest point showing the most intense characteristics of burning

What is a substrate control in a fire scene investigation?

A thorough sampling of similar but uncontaminated control specimens from another area of the fire scene

What is the easiest way to recover accelerant residues from fire-scene debris in the laboratory?

Heat the airtight container in which the sample is sent to the lab.

What are two methods for locating traces of flammable liquid residues at a fire scene?

Using a vapor detector (sniffer) or a trained canine