Forensic Serology and Biology Exam 1 Review

What does a presumptive test indicate?

A presumptive test indicates that a substance is likely or possibly present.

What does a confirmatory test prove?

A confirmatory test definitively proves exactly what the substance is.

Evidence Analysis Hierarchy

Detection , Identification , Classification, and Individualization.

What is LOD?

The lowest concentration that can be detected.

What is LOQ?

The lowest concentration that can be accurately quantified.

Chemiluminescence

Emission of light from a chemical reaction without requiring external light

Detection vs. Enhancement

Detection locates hidden or dilute bloodstains Enhancement visualizes detail

Ethics: 'We' vs. 'I' & Bad Actors

'I' ethics governs individual moral choices, while 'We' ethics reflects organizational culture. A single bad actor destroys public trust, overturns convictions, and ruins lab credibility.

Joyce Gilchrist Case

forensic chemist whose misconduct (overstating, falsifying, withholding evidence) impacted death penalty cases and led to overturned convictions after a 2001 FBI audit.

Annie Dookhan Misconduct

Massachusetts drug chemist convicted of dry-labbing, faking standards, and perjury, driven by productivity pressure; highlighted systemic lab oversight failures.

2009 NAS Report Ethical Themes

1. Competence and honesty in casework

2. Scientific integrity and objectivity

3. Transparency and full disclosure

4. Institutional accountability and independent oversight.

National Code of Ethics

Unified code created to establish standardized ethical rules across forensic disciplines, ensuring scientific objectivity, accuracy, and clear reporting.

Definition of Forensic Serology

The scientific detection, identification, and characterization of bodily fluids (blood, semen, saliva, vaginal secretions) associated with legal matters.

What do enzyme tests rely on?

Catalytic chemical reactions.

What do antibody tests rely on?

Specific immunological antibody-antigen binding.

Location of Antigens in Blood Typing

Antigens are on the surface membrane of red blood cells, with carbohydrate and protein structures determining ABO and Rh blood groups.

Immunochromatographic Cassettes

Lateral flow tests where sample travels via capillary action, binding mobile dye-labeled Ab. The Ag-Ab complex is captured at the Test line by fixed Ab, while unbound Ab forms the Control line.

High Dose Hook Effect

Excess target antigen saturates both mobile dye-bound Ab and fixed capture Ab, preventing sandwich formation and causing a false negative. Resolved by diluting the sample.

Anti-Human Serum Production

Serum containing anti-human antibodies created by injecting human antigens into an animal to generate specific antibodies.

ELISA

Enzyme-Linked Immunosorbent Assay uses antibody-antigen binding tied to an enzymatic color reaction, where absorbance or color intensity correlates with target antigen concentration.

What percentage of whole blood is made up of red blood cells?

Approximately 45% of whole blood is made up of red blood cells.

What is serum?

Serum is plasma without clotting factors.

White Blood Cells (WBCs)

Nucleated immune cells (granulocytes, lymphocytes, monocytes). Though a minority of cellular content, WBCs are the primary source of nuclear DNA in bloodstains.

ABO Blood Typing Mechanics

RBCs mixed with Anti-A or Anti-B antiserum. Agglutination (clumping) indicates the presence of that surface antigen (e.g., clumping in Anti-A indicates Type A blood).

ABO secretor percentage

Landsteiner; Approximately 80% of individuals are secretors who secrete soluble ABO antigens in bodily fluids

Rh Factor

determines positive or negative blood status.

Hemastix / TMB Test

Presumptive test using tetramethylbenzidine on a plastic strip that is oxidized by heme, turning from yellow to green or blue.

Leuco Crystal Violet (LCV)

Presumptive test involving heme-catalyzed oxidation of LCV to a dark violet/purple color, used specifically for enhancing latent bloody prints.

Amido Black

Enhancement test that stains general protein contentdark blue/black.

Takayama Test

Confirmatory microcrystal test where blood is heated with pyridine and glucose to form pink pyridine hemochromogen crystals, offering high specificity and virtually no false positives.

Hexagon OBTI

Confirmatory immunochromatographic cassette detecting human hemoglobin via a pink test line. Subject to a rare high-dose hook effect causing false negatives.

Luminol

Presumptive chemiluminescence test, produces blue-white light. Requires total darkness and has a short-lived glow.

Fluorescein

Presumptive test where heme oxidizes fluorescin to fluorescein, yellow-green fluorescence under ALS (455 nm). Does not require total darkness and does not destroy DNA.

Bluestar Forensic

Presumptive test using an optimized luminol formulation that produces intense blue chemiluminescence without requiring total darkness and does not destroy DNA.

Peripheral vs. Menstrual Blood

Peripheral blood circulates in vessels and clots normally. Menstrual blood contains endometrial tissue, vaginal flora, glycogenated squames, LDH, and degraded fibrin products (D-dimers).

Forensic Significance of Menstrual Blood

Differentiating blood types and origins is crucial in sexual assault or violent crime investigations to corroborate(trauma vs. normal menstruation).

Semen Components & Organs

Cellular component (~5%) consists of spermatozoa from the testicles. Fluid plasma (~95%) comprises seminal vesicle fluid (~60%), prostatic fluid (~30%), and bulbourethral fluid (~5%).

Spermatogenesis Progression

Spermatogenesis is the full maturation process of sperm cells in the seminiferous tubules over approximately 64-74 days. Spermatocytogenesis is the initial phase of cellular division.

Sperm Anatomy & Key Enzymes

Head contains nuclear DNA, acrosome is the enzyme cap, midpiece has mitochondria, and tail provides motility. Key enzymes include semenogelin (coagulation) and PSA/p30 (liquefaction marker).

Sperm Metrics & Azoospermia

Normal sperm count is 15-200+ million/mL with potential head/tail dysmorphology. Azoospermia is the complete absence of sperm cells in semen due to vasectomy, blockage, or failure.

Azoospermia

No sperm in semen

Aspermia

no seminal fluid produced

Oligospermia

low sperm concentration, <15 million sperm per milliliter.

Teratozoospermia

high percentage of sperm are deformed

Monoclonal Antibodies

Laboratory antibodies from a single B-cell clone; recognize one specific epitope.

Polyclonal Antibodies

Heterogeneous antibody mixture from multiple B-cell clones; recognize multiple epitopes.

polyspermia

high sperm count

LMG

leucomalachite green. presumptive test for blood, oxidized with hydrogen peroxide

Phenopthalein

presumptive test for blood, oxidized with hydrogen peroxide