Forensic DNA Analysis – Lecture Overview

Vocabulary flashcards summarizing key terms, biological sources, and testing methods discussed in the lecture on forensic DNA analysis.

DNA (Deoxyribonucleic Acid)

Molecule that encodes proteins and controls body functions; basis for forensic identification.

Coding DNA

~3 % of the genome that contains genes used to make proteins.

Non-coding DNA ("junk DNA")

~97 % of the genome that does not code for proteins; source of most forensic markers.

STRs (Short Tandem Repeats)

Short, repeated DNA sequences in non-coding regions used to differentiate individuals.

Nuclear DNA

DNA found in a cell’s nucleus; unique to each person (except identical twins) and standard for forensics.

Mitochondrial DNA

DNA located in mitochondria, inherited maternally; useful when nuclear DNA is degraded or missing.

Autosomal DNA

DNA on non-sex chromosomes inherited from all ancestors; basis for genetic genealogy.

Y-Chromosome DNA (Y-STR)

Markers passed down the paternal line; helpful in male identification and mixed samples.

Nucleotide Base Pairs

Adenine–Thymine and Cytosine–Guanine pairs that form the rungs of the DNA ladder.

FBI Core Loci

Twenty designated STR locations the FBI uses to compare DNA profiles (up from the original 13).

Identical Twin DNA

Twins who develop from one fertilized egg share the same nuclear DNA profile.

Blood

Fluid consisting of RBCs (no DNA), WBCs (contain DNA), and plasma; common DNA source via WBCs.

Red Blood Cells (RBCs)

Oxygen-carrying cells lacking nuclei and DNA.

White Blood Cells (WBCs)

Nucleated blood cells that provide the DNA in blood samples.

Plasma

Liquid component of blood (≈90 % water) that carries cells and solutes.

Presumptive Blood Test

Initial chemical test to indicate the possible presence of blood at a scene.

Semen

Fluid containing spermatozoa; appears whitish, fluoresces under ALS, rich DNA source.

Acid Phosphatase (AP) Test

Colorimetric test detecting the enzyme abundant in semen to locate seminal stains.

Alternate Light Source (ALS)

Broad-spectrum light tool that causes semen and other substances to fluoresce for visual detection.

Choline & Spermine Crystal Tests

Microscopic methods confirming semen by forming characteristic crystals.

Azoospermia

Condition where semen lacks sperm cells; AP test can still identify the fluid.

Touch DNA

DNA obtained from only ~18 shed epithelial (skin) cells left on objects or surfaces.

Glycogenated Epithelial Cells

Vaginal wall cells containing glycogen; marker used to confirm vaginal secretions.

Saliva

Fluid of mostly epithelial cells plus enzymes (e.g., amylase); common on evidence like cups or bite marks.

Amylase Test (Phadebas)

Color test for salivary alpha-amylase to indicate saliva presence.

RSID-Saliva Test

Immunoassay that detects human-specific alpha-amylase in saliva samples.

Urine

Generally poor DNA source but may contain epithelial cells and WBCs; identified by urea and creatinine.

Hair & Bone DNA

Hard tissues that can yield DNA when soft-tissue sources are absent; require specialized extraction.

Accelerant Swabbing

Collecting from containers or surfaces that held flammable liquids in arson cases.

Forensic Genetic Genealogy

Using autosomal DNA and family trees to identify suspects or victims (e.g., Golden State Killer).

Case Context

Interpretation of DNA’s body-fluid origin and location to build a legally meaningful narrative.

Buccal Swab

Cheek-cell collection method for reference DNA samples from victims, suspects, or relatives.

Alpha-Amylase

Enzyme abundant in saliva; target molecule for saliva detection tests.