Forensic BIO

• ABO blood groups, Karl Landsteiner (1900): studying blood transfusion reactions
• Four blood groups: A, B, AB, O
• Blood type is inherited, and frequencies in the population differ
• First polymorphic antigen marker
• High probability of coincidental match

• Approximately 100 protein polymorphisms had been discovered by the 1980’s
• Commonly used systems: erythrocyte enzymes, serum proteins, hemoglobin
• Combining blood group typing and protein polymorphisms, the chance of coincidental match was reduced

• DNA fingerprinting (VNTRs – variable number tandem repeats)
• mid-1980’s: Kary Mullis – PCR (polymerase chain reaction)
• Single nucleotide polymorphisms (SNPs): HLA-DQA1, Polymarker (PM)
• Amplified fragment length polymorphism (AMP-FLP): D1S80
• Short tandem repeats (STRs): CODIS loci· Samples only Valid when reference sample is present Y-STRs
• Mitochondrial DNA
• SNPs

• Probative: Having the effect of proof, tending to prove, or actually proving
• Probative evidence establishes or contributes to proof

• Priority – based on probative value
• Corpus delecti (“body of crime”) – demonstrates a crime has occurred
• Evidence that can establish connections between victim-perpetrator
• connections between victim-scene, perpetrator-scene
• Case-to-case linkage

• Begins only after entire scene is documented
• Can be accomplished in a number of ways:
• Removal of small items to the lab
• Swabbing: of an item’s surface (preferred method for hard items, such as countertops or desktops)
• Cutting: useful with soft items, such as fabric, from which areas of interest may be removed
• Tape-lifts: areas of interest are sampled with a piece of tape to remove any cells that may be present
• Scraping: the surface of items are scraped with a blade to remove deposited cells. A small “pile” of fiber, debris and cells is produced

• multiple analysis of evidence (bloodstain patterns, fingerprints, etc)
• trace evidence
• control samples
• Run (+) and (-) controls
• (+) = proper technique
• (-) = Contamination
• size of sample
• wet evidence

• Hematapoetic lineage cells: red blood cells, white blood cells, and platelets
• in a protein-aqueous fluid called plasma
• Serum: the fluid excluded from blood once it has clotted (serum is simply plasma minus the proteins responsible for the clotting process, primarily fibrinogen and fibrin)

• Red blood cells (erythrocytes)
• Mature RBC do not have nuclei à no nuclear DNA

Heme: binds oxygen

White blood cells (leukocytes): immune cells, have nuclei, are the main source of nuclear DNA in blood

• Platelets (thrombocytes): play a role in blood clotting
• Do not have nuclei, therefore do not have nuclear DNA

• Assay for the activity of the heme component of blood
• Heme catalyzes a redox reaction (i.e. has peroxidase activity)

• Hydrogen peroxide (H2O2) is typically used as the oxidizing agent (H2O2 is reduced)
• Heme is the catalyst (catalyst: increases the rate of reaction by reducing activation energy, but is not itself consumed)
• A colorless substrate is oxidized (loses electrons to H2O2) to a product with color, chemiluminescence or fluorescence

• Kastle-Meyer
• Leuchomalachite Green
• Tetramethylbenzidine (TMB)