Midterm Exam Study Guide

Stages of modern forensic biology

Antigen Polymorphism, Protein Polymorphism, DNA Polymorphism

Highest priority evidence

Corpus delicti -Items that establish connections between 2 or more items should also be given higher priority such as an item that links the suspect to the crime or to the victim

Impact spatter

Created by force applied to liquid blood source. Will form larger drops and be more concentrated in the areas directly adjacent to the action

Subdisciplines of forensic science

Crime Scene Investigation, Pattern evidence analysis, Forensic Biology, Toxicology, Trace Evidence Analysis, Controlled Substance Analysis, Fire/explosion Debris Analysis, Questioned Document Analysis, Computer Forensics, Forensic Pathology

Phases of BPA

Pattern analysis - looks at the physical characteristics of the stain patterns including size, shape, distribution, overall appearance, location and surface texture where the stains are found. Analysts interpret what pattern types are present and what mechanisms may have caused them, Reconstruction - Uses the analysis of data collected to put contextual explanations to the stain patterns: what type of crime has occurred? Where is the person bleeding from? Did the stain patterns come from the victim or someone else? Are there other scene factors that affected the stain patterns?

Know what things can impact the shape of a blood stain

If the object impacts liquid blood, the larger surface area will collect more blood, producing drops of varying sizes

Determining child's blood type from parents

If you inherit an A from one parent and an O or A gene from another parent, you will have type A blood. Type B from one parent and type O or another type B gene from the other parent will give you type B blood. But inherit an A gene from one parent and a B from the other and you have AB type blood. Those with type O blood have inherited the O gene from each parent.

Amylase

Indicates the presence of saliva

mtDNA inheritance

Inherited from mother

Platelets

Play a role in blood clotting, gather at sites of injuries, (no nuclei/no DNA)

Monoclonal antibodies

Specific, homogenous, and unlimited quantities

Parts of a blood drop

Spines, Satellites, Tails

Search types

Spiral, Grid, Strip, Quadrant, Zone

Zone of Equivalence

Maximum level of precipitation occurs in this zone. As the concentration of antigen increases, the amount of precipitate increases since the ratio of antigen to antibody is optimal, cross-linking occurs.

Gunshot injury

Mist-like spatter caused by bullets entering and exiting the body

Reading results of tests like RSID kit

negative-line on C Positive-line on C T Invalid-line on T

Primary reactions

nitial binding of 1 epitope of an antigen (Ag) to 1 binding site of an antibody (ab) to form an antigen-antibody complex

Alec Jefferys

developed a revolutionary technique using VNTR(variable number tandem repeats). The greater individual variability in DNA polymorphisms allows for a very low probability that 2 unrelated individuals will have the same DNA profile

Affinity

energy of the interaction of a single epitope on an antigen and a single binding site on a corresponding antibody. The bond strength depends on the specificity of the antibody for the antigen.

Avidity

overall strength of the binding of the antibody to the antigen. It is basically the sum of the binding affinities of all the antigen-antibody binding sites. It also reflects the overall stability of an antigen-antibody complex.

Kastle-Meyer positive test (Phenolphthalin Assay)

phenolphthalin(1901), a colorless substance, is catalyzed by heme with hydrogen peroxide as an oxidant. It will turn PINK in the presence of blood

Epitope

portion of the immunogen that is recognized by the antibody. Each epitope can cause the production of its own antibody

Polyclonal antibodies

produced when an immunogen is introduced into a host animals such as a bird(B), Rabbit(R), or horse(H)

Expert witness vs. non-expert witness

qualified based on their knowledge, skill, experience, training or education as such they can give an opinion to the court which is relevant to the tests performed

Range of BPA

range from investigation and analysis of bloodstain patterns at the crime scene to bench work in the laboratory analyzing and DNA profiling the blood. Limited analysis can also be done using only photographs of the scene

Most abundant secretion in seminal fluid

seminal fluid which accounts for about 60% of the total ejaculate amount

Class characteristics

set of characteristics that allow a sample to be placed in a category with similar materials

Immunogen

foreign substance that can cause antibody formation when introduced to a host.

Know the main/most important reasons to use BPA

function of bloodstain pattern analysis is to support or corroborate witness statements and laboratory and post-mortem findings

Sharp force injury

injuries are caused by an object with a relatively small surface area, such as an ice pick or a knife. less blood is deposited on the instrument, resulting in a smaller, more linear pattern of stains

Order of testing multiple evidence

item of evidence is going to have to undergo more than 1 type of testing the non-destructive test should be performed first

Karl Landsteiner

ABO blood groups were discovered in 1900. he found there were four groups of human blood cells (A, B, AB and O). All these studies lead to another sub discipline called Forensic Serology.

Most commonly used blood group system

ABO system

Special considerations for packaging types of evidence

Air dry before packaging, Do not group items together, Dry before folding, use clean paper between parts

Fluorescence of saliva stains

Saliva stains usually have a less intense fluorescence than that of semen stains

Bodily fluids found at crime scenes

Saliva, Blood, Urine, Semen, vomit, vaginal secretion and fecal samples.

Role of 1st responding officer

Securing and protecting the scene, evacuating people, detaining suspects, questioning witnesses, call EMS if anyone is injured.

Composition of semen

Seminal fluid and sperm cells

Cross-reaction

antibodies bind with lower strength to antigens that are similar in structure to an antigen immunogen

Postzone

at this point the amount of antigen is in excess so each antibody is saturated with antigen and cross-linking can not occur so no precipitate is formed

Prozone

at this point the antibody is in excess so each antigen molecule is saturated with antibody, preventing cross-linking and no precipitate is formed

Saliva production per day

1.0 to 1.5 liters

Cast-off pattern

Bloodstain pattern from blood drops released from an object due to its motion

Back spatter

Bloodstain pattern from blood drops traveling in the opposite direction of external force applied. (large and fewer drops)

Forward spatter

Bloodstain pattern from blood drops traveling in the same direction as impact force. (mist mist)

Blunt force injury

Caused by an object with a larger surface area. object impacts liquid blood, the larger surface area will collect more blood, producing drops of varying sizes.

Projection spatter

Caused by arterial spurting, expirated spray, or spatter cast off an object

Most common staining technique for sperm

Christmas tree stain, Nuclear Fast Red (NFR) is a dye used for staining the nuclei red in the presence of aluminum ions, Picroindigocarmine (PIC) is the component that stains the neck and tail portions green. The middle section will stain blue and the acrosomal cap will stain pink.

CODIS

Combined DNA Index System, uses 13 STR loci database.

Kary Mullis

Developed a technique (Polymerase Chain Reaction (PCR)) that amplifies a small quantity of DNA. This revolutionized forensic DNA analysis by making it possible to obtain accurate DNA profiles when only minute amounts of DNA can be recovered from a crime scene.

Types of PPE

Disposable coverall body suits, Face mask, Safety eye glasses or goggles, Disposable gloves, Disposable shoe covers, Disposable hair net

Methods for documenting crime scenes

Drawing sketches, Taking photographs, Taking videos

Fluorescence of semen

Flavin is the substance that causes semen to fluoresce under UV light

Plasma

Fluid portion of blood

Antigen

Foreign substance that reacts with an antibody

Chain of custody

Form filled out whenever evidence is handled or transferred, prevents tampering and contamination

White blood cells

Granulocytes, Lymphocytes, Monocytes, defend against infection. ( have a nuclei/main source of DNA from the blood)

Parts of a sperm cell

Head, middle, tail

Amylopectin

Highly branched and consists of linear chains of glucose residues

Red blood cells

Lifespan of about 3 months, no nuclear DNA(no nuclei), consist of hemoglobins, The proteins responsible for transporting oxygen. Adult hemoglobin is designated as α2β2

Amylose

Long, unbranched chains of glucose residues (starch reacts strongly with iodine to form a dark blue color and amylopectin turns reddish-purple)

Void patterns

Occurs when a person or object blocks the path of the blood

Y chromosome inheritance

Passed from father to son

Types of bloodstains

Passive stains - include drops, flows and pools, and typically result from gravity acting on an injured body, Transfer stains - Result from objects coming into contact with existing bloodstains and leaving wipes, swipes or pattern transfers behind, Projected or impact stains - Result from blood projecting through the air and are usually seen as spatter, but may also include gushes, splashes and arterial spurts, Blood spatter is categorized as impact spatter(created when a force is applied to a liquid blood source) or projection spatter (caused by arterial spurting, expirated spray or spatter cast off an object)

Positive result for Fast Blue

Purple color within 1 minute, positive for semen.

Evidence markers

Taking photographs - should include scales such as a ruler or other marker for accuracy of the size reference later, Numbers the evidence found on a crime scene.

Locard Exchange Principle

cross-transfer of evidence occurs whenever a a perpetrator has any physical contact with an object or person

Leucomalachite Green positive test (LMG)

Triphenylmethane dye (colorless) that turns green under acidic conditions (hydrogen peroxide as the oxidant)

Types of linkages established by evidence

Victim-to-scene, perpetrator-to-scene

Questions answered by BPA

What occurred? Where did the events occur? When and in what sequence? Who was there? What did not occur?

Antibody

a blood protein produced in response to and counteracting a specific antigen. Antibodies combine chemically with substances which the body recognizes as alien, such as bacteria, viruses, and foreign substances in the blood.

ABO blood typing

allows you to narrow the suspect field based on the 4 blood types, useful for excluding suspects than including them because there is a high probability that any 2 randomly selected people could have the same blood type.

Expiration pattern

bloodstain pattern resulting from blood forced by airflow out of the nose, mouth, or a wound

Confirmatory test characteristics

can be done visually via microscope, PSA identification via immunochromatographic assays, ELISA (Enzymes-Linked Immunosorbent Assay) or with RNA-based tests

Presumptive test characteristics

can not tell is AP is from semen or other fluids) such as ALF searches, colorimetric assays and fluorometric assays

Incomplete antibodies

can only perform initial binding and fails to form actual agglutination.

Complete antibodies

can perform both primary and secondary reactions that result in agglutination

Effect of vasectomies on semen

can still produce ejaculate, it will just contain only seminal vesicle and prostatic fluid. It will not contain sperm cells.

Tools used in BPA

strings and a protractor, mathematical calculations or computer models. Tools used to determine area of convergence and area of origin.

Advantages of chemiluminescence and fluorescence assays

testing and fluorescence testing is that the reagents can be sprayed over large areas to search for blood, positive reaction not only identifies blood, but can reveal patterns, such as shoe prints and blood splatter, very sensitive, as such they can locate even small amounts of blood, and useful for crime scenes that have been cleaned and show no visible signs of blood

Oxidants

these are molecules that can gain electrons from other molecules, can cause false positive results by catalyzing the oxidation reaction even without any heme. Bleach and other household cleaners are examples.

Individual characteristics

unique characteristics of both evidence and a reference sample that share a common origin to a high degree of certainty