Forensic Serology and DNA Analysis Notes

Forensic Serology and DNA Analysis

Serology Basics
  • Definition: Serology is a broad scope of laboratory tests that utilize specific antigen and serum antibody reactions.
  • Blood Composition: Blood consists of a complex mix of cells, enzymes, proteins, and inorganic substances.
Components of Blood
  • Erythrocytes (Red Blood Cells): Carry oxygen throughout the body.
  • Leukocytes (White Blood Cells): Part of the immune system, fighting infections.
  • Plasma: The liquid component of blood that remains after clotting factors are removed.
  • Platelets: Cell fragments that help with blood clotting.
Key Differences
  • Plasma vs. Serum: Plasma resembles serum but contains clotting factors; serum is the liquid part that separates from blood after clots.
Antigens and Antibodies
  • Antigens: Proteins on the surface of red blood cells that stimulate antibody production.
  • Antibodies: Proteins in the serum that destroy or inactivate specific antigens.
Blood Type Details
  • Blood Types:
    • A: Has A antigens and produces anti-B antibodies.
    • B: Has B antigens and produces anti-A antibodies.
    • AB: Universal recipient with A and B antigens but no antibodies.
    • O: Universal donor with no antigens and both anti-A and anti-B antibodies.
  • Rh Factor: A protein (also known as D antigen) that some people carry, important in blood transfusions.
Blood Testing in Forensics
  • Questions for Investigators:
    1. Is it blood?
    2. Is it of human origin?
    3. Can it be associated with a particular individual?
  • Presumptive Tests: Tests that indicate the presence of blood, e.g., Hemastix strips, Benzidine, Kastle-Meyer, Luminol test.
  • Precipitin Test: Antibody test that reacts with its corresponding antigen to form a precipitate, indicating human blood.
  • DNA Analysis: Necessary to determine the specific individual from whom the blood originated.
Importance of Biological Fluids
  • Other Fluids: Saliva, semen, and urine can also contain DNA.
  • Saliva Composition: Contains water, mucin, amylase, and buccal cells.
  • Semen Composition: Made up of water, spermatozoa, enzymes, and organic salts.
DNA Overview
  • Definition: Deoxyribonucleic acid is identical in each cell, and each person has approximately 60 trillion cells.
  • Gene: The fundamental unit of heredity within DNA.
  • Nucleotide Structure: Composed of deoxyribose sugar, a phosphate group, and a nitrogenous base (A, T, C, G).
  • Base Pairing: Specific pairing occurs between adenine & thymine and cytosine & guanine, forming double-stranded DNA (double helix structure).
DNA Typing Techniques
  • Electrophoresis: Separates DNA fragments through a gel under an electric field.
  • RFLP Analysis: Uses restriction enzymes to cut DNA into fragments based on length polymorphisms and visualizes them via electrophoresis.
  • PCR (Polymerase Chain Reaction): Technique for amplifying small amounts of DNA into millions of copies.
  • STR (Short Tandem Repeats): Modern method for DNA analysis that identifies repeating sequences and is less susceptible to degradation.
  • Multiplexing: A technique to amplify multiple STRs simultaneously, increasing the accuracy of identification.
Forensic DNA Applications and Considerations
  • CODIS: A computer database that compiles DNA profiles from convicted offenders and crime scene evidence.
  • mtDNA: Mitochondrial DNA, inherited maternally; useful in samples lacking nuclear DNA but more rigorous and costly to analyze.
  • Key Evidence Collection Points:
    • Photograph the scene before collecting.
    • Wear gloves to prevent contamination.
    • Avoid placing evidence in plastic bags and keep away from sunlight.
    • Change gloves frequently and minimize handling.