Forensic Science: Blood Types, DNA, Drugs, and Evidence Analysis

ABO blood types

Blood classification based on A and B antigens on red blood cells; used in blood typing and forensic identification.

ADME

Absorption, Distribution, Metabolism, and Excretion — describes how a drug or toxin moves through the body.

Adsorption

Molecules adhering to a surface; used in chromatography and solid-phase extraction.

Agglutinate

Clumping of red blood cells due to antigen-antibody reaction; occurs in incompatible blood mixtures.

Allele

One of two or more forms of a gene found at a specific locus on a chromosome.

Alternative light source (ALS)

Specialized lighting (UV, IR, etc.) used to visualize evidence like bodily fluids, fibers, or bruises.

Alveolar air

Air in the lung's alveoli; used in breathalyzer tests to estimate blood alcohol content.

Amylase

Enzyme found in saliva that breaks down starch; used to identify saliva stains.

Anagen phase

Active hair growth phase; contains cells rich in nuclear DNA for analysis.

Antibody

Immune protein that binds to specific antigens; used in drug and body fluid detection.

Antigen

A molecule that triggers an immune response; basis for blood typing and serology tests.

ASTM

American Society for Testing and Materials — sets forensic testing standards.

Base pairs

Complementary pairs of nucleotides (A-T, C-G) in DNA; define genetic structure.

Basepair

A single unit of two bonded DNA bases (A-T or C-G).

Blood alcohol content (BAC)

Amount of ethanol in the bloodstream; used in DUI and forensic toxicology.

Capillary electrophoresis

DNA separation method using electric fields; separates DNA fragments by size in STR analysis.

Catagen phase

Transitional phase between hair growth (anagen) and resting (telogen).

Chemiluminescence

Light produced by chemical reaction; used in blood detection (e.g., luminol).

Christmas tree stain

Microscopic stain that colors sperm heads red and tails green for identification.

Chromatography

Technique for separating mixtures based on movement through stationary and mobile phases.

Chromogenic substance

Chemical that changes color when reacting; used in presumptive blood or drug tests.

Chromosome

DNA-protein structure carrying genetic information; humans have 23 pairs.

CODIS

Combined DNA Index System — FBI DNA database used to match DNA profiles.

Confirmatory test

Definitive test that confirms the presence of a specific substance (e.g., GC-MS).

Controlled substance

Drug regulated by law due to potential abuse (e.g., cocaine, heroin).

Cortex

Middle layer of a hair containing pigment granules used for comparison.

Cuticle

Outer layer of hair shaft with overlapping scales; helps identify species.

Depressant

Substance that slows the central nervous system (e.g., alcohol, barbiturates).

Designer drugs

Synthetic versions of illegal drugs created to mimic effects and avoid detection.

Distribution

Movement of a drug or toxin through the body's tissues and fluids.

DNA polymerase

Enzyme that synthesizes new DNA strands; used in PCR.

Dose

Amount of substance taken at one time.

Electrophoresis

Technique using electricity to separate DNA, RNA, or proteins by size/charge.

Enzyme

Biological catalyst that speeds up chemical reactions; used in forensic testing.

Excretion

Elimination of substances from the body (e.g., urine drug tests).

False negative

Test result indicating a substance is absent when it is actually present.

False positive

Test result indicating a substance is present when it is not.

Fluorescence

Emission of visible light when exposed to UV light; used to detect bodily fluids.

Follicle

Hair root structure in skin; contains living cells used for DNA testing.

Fuel cell

Sensor in breathalyzers that produces current proportional to alcohol level.

Gene

DNA segment coding for a specific protein or trait.

Hallucinogen

Drug that alters perception, mood, and thought (e.g., LSD).

Hemoglobin

Oxygen-carrying protein in red blood cells; targeted in blood detection tests.

Heterozygote

Individual with two different alleles at a genetic locus.

Homozygote

Individual with identical alleles at a genetic locus.

Immunoassay

Test using antigen-antibody reactions to detect drugs or hormones.

Laminated glass

Safety glass with a plastic interlayer; used in forensic fracture analysis.

LD50

Median lethal dose — kills 50% of a test population.

Locus

Specific position of a gene or DNA marker on a chromosome.

Luminol

Chemiluminescent reagent that glows blue when reacting with blood.

Manufactured fiber

Synthetic fiber (e.g., nylon, polyester) made from polymers.

Mass spectrometry

Technique that identifies substances by measuring ion mass; used in drug and toxin analysis.

Medulla

Central core of a hair shaft; used to distinguish species.

Metabolism

Chemical breakdown of substances in the body; key in toxicology.

Microcrystalline test

Confirmatory chemical test forming unique crystals for specific drugs.

Mitochondria

Cell organelles containing mtDNA; useful when nuclear DNA is degraded.

Mobile phase

The solvent that moves through the stationary phase in chromatography.

Narcotic

Drug that relieves pain and induces sleep (e.g., morphine).

Natural fiber

Fiber from plants or animals (e.g., cotton, wool).

Nuclease

Enzyme that cuts DNA or RNA strands.

Nucleotide

Building block of DNA/RNA — sugar, phosphate, and base.

Physical dependence

Body's adaptation to a drug, causing withdrawal if stopped.

Poison

Substance causing harm or death when ingested, inhaled, or absorbed.

Polymer

Large molecule made of repeating units; found in fibers and plastics.

Polymerase chain reaction (PCR)

Method to amplify DNA from small samples.

Polymorphism

Genetic variation among individuals; used in DNA profiling.

Postmortem redistribution

Movement of drugs in the body after death, affecting toxicology results.

Presumptive test

Preliminary test indicating possible presence of a substance.

Prostate specific antigen (PSA)

Protein found in semen; used to confirm seminal fluid.

Psychological dependence

Emotional or mental need for a substance.

Random match probability

Likelihood that two unrelated individuals share the same DNA profile.

Rhesus (Rh) factor

Blood antigen determining positive or negative blood type.

Screening test

Initial test to detect possible presence of a drug or toxin.

Seized drugs

Illegal substances confiscated for forensic testing.

Selectivity

Ability of a test to detect only the target substance.

Seminal acid phosphatase

Enzyme in semen; presumptive test for seminal fluid.

Sensitivity

Ability of a test to detect even trace amounts of a substance.

Serology

Study and identification of bodily fluids.

Short tandem repeats (STRs)

Repeated DNA sequences used for forensic DNA profiling.

Spectrophotometry

Measures light absorption to identify and quantify substances.

Starch-iodine test

Test where iodine turns blue-black in the presence of starch.

Stationary phase

Fixed material in chromatography that separates components.

Stimulant

Drug that increases CNS activity (e.g., cocaine, methamphetamine).

SWGDRUG

Scientific Working Group for the Analysis of Seized Drugs — sets forensic drug testing guidelines.

Touch DNA

Trace DNA left behind from skin cells on an object.

Toxicity

Degree to which a substance is harmful to living organisms.

Toxicology

Study of poisons and their effects; forensic toxicology identifies drugs and toxins in biological samples.