Biological Evidence: Blood, Hair, Semen (Forensic Topics)

A set of vocabulary-style flashcards covering key terms and concepts from the lecture notes on biological evidence, fibers, glass, and tool marks.

Blood

The body's circulating tissue composed of plasma and formed elements; about six quarts in an adult male.

Plasma

Straw-yellow liquid portion of blood; 65% of blood; ~90% water; contains albumin, globulins, and fibrinogen.

Serum

Liquid portion obtained after blood clots and the serum stands; lacks fibrinogen and other clotting factors.

Formed elements

Cellular components of blood: erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets).

Erythrocytes

Red blood cells; carry oxygen and carbon dioxide; contain hemoglobin.

Leucocytes

White blood cells; fight infection.

Thrombocytes

Platelets; essential for blood clotting.

Hemoglobin

Iron-containing protein in red blood cells that binds oxygen and gives blood its red color.

Agglutination

Clumping of cells due to antibodies binding antigens.

Agglutinin

Antibody that causes agglutination.

Agglutinogen

Antigen that elicits the formation of agglutinin.

ABO blood group system

Blood groups defined by A and/or B antigens on RBCs; discovered by Karl Landsteiner in 1900.

A antigen

Antigen A on RBCs; present in type A; prompts anti-B antibodies in plasma.

B antigen

Antigen B on RBCs; present in type B; prompts anti-A antibodies in plasma.

Anti-A

Antibody against A antigen; found in types B and O.

Anti-B

Antibody against B antigen; found in types A and O.

Karl Landsteiner

Scientist who discovered the ABO blood group system in 1900.

Presumptive blood test

Screening tests indicating possible blood, often showing color change due to peroxidase-like activity of hemoglobin.

Benzidine test

Presumptive test detecting blood at about 1:300,000 dilution; positive blue color.

Guaiacum test

Presumptive test detecting blood at about 1:50,000; can’t detect very old stains; positive blue.

Phenolphthalein test (Kastle-Meyer)

Very sensitive presumptive test; pink color indicates blood; high sensitivity (1:80,000,000).

Permanganate test

Presumptive test producing a pink color change with bloodstains.

Leucomalachite Green Test

Presumptive test producing a green color with blood (malachite green).

Hemastix

Urine dipstick test for blood; positive green line indicates presence of blood in urine.

Luminol

Chemiluminescent presumptive test; yields light on spraying on areas with blood; useful for large surfaces.

Teichmann crystal test

Confirmatory test; positive dark brown rhombic crystals of haemin/haematoin chloride.

Takayama crystal test

Confirmatory test; positive large rhombic crystals, salmon-pink; forms in 1–6 minutes.

Spectroscopic examination

Microspectroscopy; detects characteristic oxyhemoglobin bands in stains; confirms blood presence.

Precipitin test

Species determination; antigen–antibody precipitation distinguishes human from animal blood.

Follicular tag

Nuclear DNA-rich tissue at the hair follicle; rich source for individualization.

Anagen

Active growth phase of hair; flame-shaped root; contains follicular tag.

Catagen

Transition phase; elongated root; bulb shrinks.

Telogen

Resting/shedding phase; club-shaped root; naturally shed.

Medulla

Central canal of hair; pattern varies (continuous, fragmented, absent); helps in comparisons.

Cortex

Elongated cortical cells with pigment granules; determines hair color and characteristic patterns.

Cuticle

Outer layer of hair shaft; overlapping scales oriented toward the tip; patterns include coronal, spinous, imbricate.

Medulla index

Ratio of medulla diameter to shaft diameter; human < 1/3; animal > 1/2.

Human vs animal medulla

Human hair usually fragmented or absent; animal hair often continuous medulla.

Growth phases (hair roots)

Anagen, catagen, telogen; anagen contains the follicular tag for DNA analysis.

Postmortem root banding

Dark band around hair root indicating deposition after death; seen in anagen/catagen, not telogen.

Micrometer

Instrument used to measure hair diameter precisely.

Isotope analysis

Hair grows ~1 cm per month and records local water isotopes; used for travel/t residence timeline.

Nuclear DNA in hair

Best obtained from anagen/early catagen roots or follicular tag; can individualize.

mtDNA in hair

Mitochondrial DNA from the shaft; cannot individualize; useful for inclusion/exclusion and maternal lineage.

Hair collection guidelines

Collect 25 full-length scalp hairs and 25 full-length pubic hairs from the same body area; comb area; package separately.

Spermatozoa

Male reproductive cells; sperm.

Seminal plasma

Fluid from seminal vesicles and prostate that nourishes sperm and helps movement.

Acid phosphatase test

Detects acid phosphatase enzyme abundant in semen; yields orange-red pigment.

Florence test

Produces dark-brown crystals (rhombic or needle-shaped) under a microscope for semen stains.

Barberio’s test

Yields slender yellow-tinted rhomboid needles with obtuse angles for semen.

Wet specimen (semen)

A drop of semen on a slide with distilled water; examine for sperm cells under high power.

Dried specimen (semen)

Seminal stain on fabric; gray-white or yellowish; often stiff.

UV fluorescence (semen)

Seminal stains fluoresce under UV light; not specific for semen.

PSA test

Prostate-specific antigen; confirms presence of semen.

Semen interpretation

Presence of sperm cells confirms semen; absence does not prove absence due to aspermia/oligospermia.

Fibers

Class of physical evidence; types include animal, vegetable, mineral, and synthetic.

Animal fibers

Natural fibers such as wool, silk, camel hair, fur.

Vegetable fibers

Natural plant fibers such as cotton, linen, jute, hemp, ramie, sisal.

Mineral fibers

Inorganic fibers such as glass wool and asbestos.

Synthetic fibers

Man-made fibers such as nylon, Orlon, Dacron.

Cotton fiber

Flattened, twisted fibers with thickened edges.

Flax fiber

Apex tapers; cross-section polygonal with a small cavity.

Hemp fiber

Transverse lines; cellulose content.

Jute fiber

Smooth fiber with few longitudinal or transverse markings.

Wool fiber

Outer cuticle with plating cells and margins.

Silk fiber

Manufactured silk appears structureless microscopically.

Linen fiber

Straight fibers tapering to a point.

FTIR

Infrared spectroscopy; chemical fingerprinting to identify material.

Glass (inforensics)

Amorphous solid; high viscosity and rigidity; mainly silica with additives.

Glass composition

SiO2 (silica), B2O3 (boric oxide), P2O5 (phosphorus pentoxide).

Radial fracture

Cracks radiating outward from the point of impact; primary fracture.

Concentric fracture

Circular cracks around the point of impact; secondary fracture.

Point of impact

Location where a projectile struck the glass; debris and dust patterns aid identification.

Direction of impact

Entrances are cleaner; exits may be more irregular; angle affects fracture pattern.

Depression (glass)

Typically appears on the exit side due to rebound.

First shot

In a series, the radial fracture from the first shot helps define sequence of impacts.

Toolmarks

Impressions or striations left by tools on surfaces; used for identification.

Comparison microscopy

Preliminary test comparing toolmarks with suspected tools for similarity.

Profilometry

Confirmatory test measuring surface profile (depth/shape) of toolmarks.

Refractive index

Property used in preliminary glass testing to differentiate types by light bending.

XRF

X-ray fluorescence; elemental analysis to identify trace elements in glass.

ICP-MS

Inductively coupled plasma mass spectrometry; highly sensitive elemental analysis for glass.

Significance of tests

Combination of preliminary and confirmatory tests improves reliability in forensic conclusions.