Forensic Biochem 1

Who coined the term "Every contact leaves a trace"?

Locard

It is impoossible for physical evidence to be ________

Wholly absent

What is the only thing that can diminish physical evidence?

The human failure to find it, study it, and understand it

What umbrella does DNA/Serology fall under?

Biological sciences

What is forensic pathology?

Use of autopsies to determine cause and manner of death

What are manners of death?

natural, homicide, suicide, undetermined

What is forensic anthropology?

Examination of human skeletal remains to determine age, sex, and injuries

What is forensic entymology?

Estimating time of death through the study of insects

What is forensic odontology?

Study of teeth and bite mark analysis

Serology

study of the composition and properties of the serum component of blood

Why is the term "Serology" not the best in describing the work of a serologist?

Serologists deal with other bodily fluids than the serum of the blood, including urine, saliva, sperm, and vaginal secretions

What is the "Direct to DNA argument?"

If the suspect's DNA is found, that is all that's needed for trial

What is one case presented in the powerpoints were serological evidence is essential to the case?

Sexual assualt of a female victim with an object. Defense could state that the woman had natural contact with the object prior to the alleged incident, but presence of vaginal secretions would disprove this

Why would blood on a victim's clothing adjacent to a wound be example of poor probative evidence?

It is presumed that there will be victim's blood around an open wound, and there would be low chance of getting a suspect's profile

Why is semen on a suspect's underpants considered poor probative evidence?

Since the item belongs to the suspect, it could have stemmed from consensual activity

Why is semen on bedding and other items belonging to the suspect poor probative evidence?

Since they belong to the suspect we would expect their own bodily fluids to be present

What is the order in which evidence is processed at the crime scene?

Record, collect, preserve

What is the preferred method of collection at a crime scene?

Evidence should be packaged dry or dried at the scene if possible, and then stored in breathable containers prior to final storage

What should be done if an item must be folded before packaging?

Paper should be placed between parts of the garment

List the collection mode for stains, and the order in which they should be used (1 being the most desired method)

1. Collect the entire item 2. Cut the stain from a larger item 3. Transfer the stain with DI water and cotoon swab 4. Scrape or chip a non-porous surface

What must be collected alongside stains at a crime scene?

Control samples should be collected in the same manner that the stain was

What are some physical conditions that can result in the degradation of evidence?

heat, light, humidity

What does ALS stand for?

alternative light source

What is ALS and how is it used?

ALS is light at different wavelengths, which causes some biological fluids to flouresce

What are some examples of alternative light sources?

visible, UV, laser, high intensity quartz

True or false: ALS only flouresces for bodily fluids. Explain.

False, will test positive for bleach

What are some examples of a reference sample?

blood, hair, saliva from members of the investigating team, consensual partners, or members of the house

How much of human body weight is comprised of blood?

8%

How many pints of blood is in the average adult human?

8-12 pints

What is plasma?

The fluid portion of blood, comprised mainly of water

What is serum?

Plasma without the clotting factors

What percentage of blood is plasma?

55%

What types of cells can be found in the blood?

red blood cells, white blood cells, platlets

What percentage of blood is cells?

45%

What is another term for white blood cells?

Leucocytes

What is another word for platlets?

thrombocytes

What is another word for red blood cells?

Erythrocytes

What part of the blood can DNA be found?

white blood cells

What is the role of hemoglobin?

transport oxygen

What is heme?

ring with nitrogens that holds ferrous iron. The iron then binds to oxygen

What other compounds can heme bind to?

carbon monoxide and cyanide

What are catalytic presumptive tests?

Based on oxidation-reduction reaction. A colorless substrate is oxidized to produce a color change

How to catalytic presumptive tests select for blood?

Heme has peroxidase-like activity

What is the peroxidase reaction?

H202 is broken down to form a free radical O which can oxidize a substrate

In a peroxidase reaction, what is the visual difference between the reduced and oxidized form?

The reduced form will be colorless while the oxidized form will have color

What are two examples of peroxidase/catalytic presumptive tests?

Hemastix and luminol

Why are catalytic methods for testing blood considered "sensitive but not specific?"

While they're good at testing blood they will also produce many false positives for bleach and metals

What are the Teichmann and Takayama tests?

Rely on chemical reactions with blood to form pink cyrstals that can be observed under the microscope

What are the two methods of doing a species ID?

Ouchterlony plates or immunochromatographic assays

Explain the ouchterlony plate method.

A double diffusion gel, meaning both antibodies and antigens are moving. The antibodies will detect human blood and move towards the surrounding wells if it's present. This will form a precipitate known as the line of identity

Explain what the sample well of hematrace test is comrpised of

mobile monoclonal anti-human hb-dye conjugate

Explain what is in the test zone of hematrace

immobile polyclonal antihuman Hb

Explain what is in the control zone of hematrace

immobile anti-human Ig antibody

Breifly explain how a positive result immunochromatograph assay works

A sample is introduced to a sample well where antibodies are bound to dye. If human blood is present, the antibodies will bind to the blood and then will stop at the immobile test line, which is comprised of more antibodies.

Breifly explain how a negative result on an immunochromatograph assay would work

The sample zone would not bind to the sample and would therefore not bind to the test zone, either. However, the antibodies of the control zone will bind to the mobile phase regardless of whether or not the test is positive. This serves to prove that the mobile phase did move

Briefly explain the high dose hook effect.

The high dose hook effect is a form of false negative. There is too much sample introduced into the test versus the dye-bonded antibodies. This means that the undyed antigens will bind to the control center first since they're lighter, and the positive line will not be visible.