Forensic Science EXAM #1 (Evidence, Education, CSI, Blood, Body Fluids, DNA, Trace Evidence) (copy)

What cells are found in semen?

Sperm cells

Why would sperm count be lower in some males?

Due to genetics, drugs, alcohol, or a vasectomy

How does semen appear under alternate light?

Appears yellowish-white; glows under UV light

What is the presumptive test for semen?

Seminal Acid Phosphate (SAP) aka Brentamine Fast Blue Test or AP Spot Test

What are the two confirmatory tests for semen?

Christmas Tree Stain (of sperm cells) & Prostate-Specific Antigen (PSA)

What is the method and color change for the AP Spot Test?

1. moisten swab with water
2. rub swab over semen stain
3. reagent is dropped on swab
4. PURPLE color reaction

What are some false positives for the AP Spot Test?

urine, vaginal secretions, sweat; old semen stain may produce weak reaction

What is the method for the Christmas Tree Stain?

1. take swab and tease apart fibers in a drop of water on a microscope slide
2. dry the slide
3. stain with red dye and rinse, then stain with green dye and rinse

What is the method for the PSA tests?

1. swab agitated in water
2. drop of this solution added to test well
3. liquid moves through result well
4. C and T line should show for positive result

What enzyme is detected in saliva tests?

Amylase (breaks down starch)

What is the presumptive test for saliva?

Phadebas Reagent

How to use Phadebas method?

1. place stain in a tube
2. add phadebas tablet; heat tube
3. sample is centrifuged
4. color is released into top liquid
5. look for dye at the top of the tube; blue color

What are the false positives for the Phadebas test?

urine or sweat

Why are saliva stains not usually tested before moving on to DNA testing?

We aren't questioning on whether it's blood or semen, saliva can be inferred

What does DNA stands for?

Deoxyribose Nucleic Acid

What does DNA do for a living thing?

contains genetic information; codes for the proteins our bodies make that are necessary for survival

What is the molecular appearance of DNA?

Double Helix structure

What are the building blocks of DNA?

\-Sugar Phosphate (Sides of double helix)

\-Nitrogenous Base (rungs of double helix)

Where are the bases located in DNA?

Attached to a nucleotide in the ladder of DNA

What are the four bases of DNA?

Adenine, Guanine, Cytosine, Thymine

How do the four bases pair with one another?

Adenine = Guanine (AG)

Cytosine = Thymine (CT)

How many base pairs are in one copy of DNA?

Three Billion

What is the percentage of DNA sequence that is the same among humans?

99.8%

Where is DNA located in a cell?

In the nucleus (brain) and in the mitochondria

Where is the DNA located in the nucleus?

In chromosomes

How is DNA organized in cells?

In the chromosomes: -46 chromosomes, 23 pairs (mom and dad)

Where are cells located in different parts of the body?

White blood cells, sperm cells, cheek cells, saliva, tissue, bone, teeth, hair, maggot crops

What are the 3 ways DNA can be different among individuals?

1. base pairs can be different
2. base pairs can be added or removed
3. regions of DNA can be repeated

Which difference is used by FS to identify an individual?

Repeated DNA; look at a certain area of cells to determine how many times it's repeated

What is an unknown sample?

*any type of evidence found* blood stain, semen stains, saliva residue, hair, bones, teeth

What is an known samples?

blood or buccal swabs from suspect or victim or other known person (cheek swab)

How should DNA evidence be packaged?

\-Packaged individually

\-Paper bags, not plastic

\-Keep at room temperature, out of the sun

What are the forensic markers that are used in the FBI database?

Short Tandem Repeats (STRs) & Mitochondrial DNA

What are Short Tandem Repeats (STRs)?

Located in chromosomes; repeated sets

What is a locus?

the location of the STR on the chromosome

What is an allele?

it refers to the type of DNA; the number of repeats (Ex. 7,9)

What is an example of a locus?

D5S818

What makes up a locus?

DNA, chromosome \#, genome location

Why are there 13 loci used in the FBI database?

The 13 areas show a number of characteristics that are easily shown

What happens during extraction?

DNA is separated from sample

What happens during amplification (or pcr)?

Amplifies small portions of DNA (STR regions); creates up to 10 million copies

How would a FS present a matching profile in court?

The frequency of this DNA profile in a given population is 1 in 300 trillion...

When would a non-matching profile give a definite no?

If one of the 13 loci do not match; DNA does not change over time

How many base pairs are in the mtDNA genome?

16, 569 letters long

How many base pairs are analyzed in mtDNA?

900 base pairs

How is mtDNA analysis more useful than STR analysis?

\-can be used on old or degraded samples

\-can be amplified

\-multiple copies in each mitochondria in each cell

What are the limitations of using mtDNA?

it can only be described by the 900 letters

Which cell is mtDNA found in?

the egg cell; from your mother

What two types of light are used with microscopes?

reflected or transmitted light

What is reflected light?

when light bounces off the surface of an object under the microscope

What is transmitted light?

when light is passing through the object on a microscope

What are the two types of microscopes?

Stereo Binocular Microscopes & Compound Microscopes

What objects can be viewed with a Stereo Binocular Microscope?

\-search for small fibers, hairs, etc

\-looking at 3D objects

\-using reflected light

What objects can be viewed with a Compound Microscope?

\-transparent object; transmitted light

\-look through object

\-fibers, hair, glass, biological samples for sperm cells, microcrystalline tests

What type of light does a Stereo Binocular Microscope use?

Reflected Light

What type of light does a Compound Microscope use?

Transmitted Light

This is a Stereo Binocular Microscope

This is a Compound Microscope

What is an Ocular Lens?

Lens in the eyepiece of a microscope

What is an Objective Lens?

Lens above the sample in a microscope

What is a micrometer?

a ruler int he eyepiece; allows for measurement of sample

What is magnification?

the amount the object is enlarged

What is working distance?

distance between the object and objective lens

What is a PLM Microscope?

Polarized Light Microscope

\-takes advantage of the optical properties of glass, crystal, and fibers

\-sample absorbs light differently ==depending== on its ==orientation== in polarized light

What is a Comparison Microscope?

\-an optical bridge allows viewing of evidence side by side

\-useful for comparing bullets, fibers, hairs

Why should evidence items be collected separately?

it prevents trace from being transferred to other objects

What is the Locard Exchange Principle?

whenever there is contact between two objects, they will leave or pick up debris from the other object

What are the 3 methods for collecting trace evidence?

1. Visual Inspection
2. Tape Lift
3. Vacuum

What is Visual Inspection?

\-using naked eye or hand lens

\-evidence removes and packages for later analysis

\-use bright light and forceps to collect

What is Tape Lift?

repeatedly apply clear tape to small area until most of the stickiness is gone

What is Vacuuming?

\-nozzle is short and transparent

\-debris collected on a filter or membrane

Why is vacuuming often misused by investigators?

It often results in the collection of a lot of irrelevant materials

What are filaments?

long continuous fiber (silk)

What is a staple?

a filament that is cut into smaller pieces; staples are spun into thread (cotton)

What is a natural fiber?

found in nature; comes from and animal, plant, or mineral

What are examples of natural fibers?

wool (sheep), silk (silkworm), cotton (plant)

What are synthetic fibers?

made from a vat of chemicals that solidifies when it hits the air; mimics other fibers

What are examples of synthetic fibers?

nylon, polyester, acrylic

What is a refractive index?

a number that describes the ratio of the speed of light in a vacuum to the speed of light in the fiber

What are the class characteristics of fibers?

chemical composition (nylon, polyester, acrylic); other elements (chlorine)

How are fibers analyzed?

Using Microspectrophotometry (IR) that determines the chemical make up of fibers

What is a radial crack?

cracks that began at the origin of impact and spread out (pizza slice)

What is a concentric crack?

cracks that form between radial cracks to connect them (spider web)

How do we measure the refractive index of glass?

Place glass in different oils that have different refractive indexes to make the halo around the glass disappear

What is a Beke line?

the thick outside line around a sample of glass that shows that the RI of glass and oil are different

What is a conchoidal line?

cylinder like lines that point back to the origin of the impact

How to help identify the order and direction of fractures in glass?

Look at where radial fractures end into other fractures; the ones it ends into was there first

What type of relief do we look for in the RI of glass?

Low Relief \= no Beke line means that the RI and oil are similar

How are the chemical components of paint measured?

Infrared Spectroscopy (layers of paint can be analyzed to find chemical composition)

How is GSR analyzed?

\-hand is swabbed

\-swab is analyzed using (SEM/EDS) & looking for high levels of barium and antimony

What are the two elements detected in GSR?

Barium & Antimony

What is GSR?

a mixture of materials that originate from the firing of a gun and fall onto shooter's hand or clothing

Why should we not testify about guilt or innocence?

FS obtain circumstantial evidence; only helping the jury understand what we did and help them understand it

What is the first career category?

Investigation

What is the second career category?

Laboratory Work

What do Investigation Jobs do?

\-police investigate crimes \n -receive the information \n -make an analysis \n -DO NOT question suspects

What are the degree requirements for an Investigation Job?

A degree is not always required

What do Crime Laboratory Jobs consist of?

Conduct lab analysis

What are the degree requirements for Crime Laboratory Jobs?

Degree is required; usually a natural science degree (BS in chemistry, biology)

What do forensic pathologists do?

\-Conduct autopsies;determine cause of death \n -Have an MD degree