Forensic Serology and DNA Analysis Notes

Forensic Serology and DNA Analysis

Serology

  • Definition: A broad scope of laboratory tests that utilize specific antigen and serum antibody reactions to detect substances like blood.

Basic Concepts of Blood

  • Blood Composition: A complex mixture of cells, enzymes, proteins, and inorganic substances.

  • Main Components:

    • Erythrocytes (Red Blood Cells): Transport oxygen from lungs to tissues.

    • Leukocytes (White Blood Cells): Part of the immune system; fight infections.

    • Plasma: The liquid part, which contains water, salts, and enzymes.

    • Platelets: Cell fragments that play a crucial role in blood clotting.

Plasma vs. Serum

  • Plasma: The liquid part of blood with coagulation factors.

  • Serum: Similar to plasma but without coagulation factors; used interchangeably sometimes.

Antigens and Antibodies

  • Antigens: Proteins on the surface of red blood cells that trigger the production of antibodies.

  • Antibodies: Proteins found in serum that can destroy or inactivate specific antigens.

Immunoassay Techniques

  • Common Techniques: Enzyme Multiplied Immunoassay Technique (EMIT) for detecting drugs.

  • Other Types: Radioimmunoassay (RIA).

Agglutination

  • The clumping reaction that occurs when antigens and antibodies interact.

Blood Types and Genetics

  • Blood Types:

    • Type A: A antigens, anti-B antibodies.

    • Type B: B antigens, anti-A antibodies.

    • Type AB: A and B antigens, no antibodies (Universal recipient).

    • Type O: No antigens, both anti-A and anti-B antibodies (Universal donor).

  • Rh Factor: A protein (D antigen) found on red blood cells; can be positive (Rh+) or negative (Rh-).

Genetic Inheritance

  • Alleles for Blood Types: A, B, O inherited from parents.

  • Punnett Square: A tool used to predict offspring blood types based on parent genotypes.

  • Rh Alleles: Positive (Rh+) can accept Rh- and Rh+; Negative (Rh-) can only accept Rh-.

Forensic Investigations on Blood Evidence

  • Key Questions:

    • Is it blood?

    • What species did it originate from?

    • Is it of human origin, and can it be linked to an individual?

  • Presumptive Tests: Indicate presence of blood, such as:

    • Hemastix strips

    • Benzidine

    • Kastle-Meyer test

    • Luminol test for luminescence.

  • Precipitin Test: An antibody that interacts with its corresponding antigen to form a visible precipitate.

DNA Analysis

  • Definition: Deoxyribonucleic acid, the molecule that carries genetic information.

  • Fundamental Unit: The gene, which is a segment of DNA.

  • Nucleotides: Repeating primary unit composed of:

    • Deoxyribose sugar

    • Phosphate group

    • Nitrogenous base (Adenine, Guanine, Cytosine, Thymine).

  • Complementary Base Pairing: Specific pairing of bases in a double-stranded DNA molecule.

DNA Typing and Technology

  • Electrophoresis: A technique used to separate DNA fragments.

  • RFLP (Restriction Fragment Length Polymorphism): A method for analyzing the length of DNA fragments originating from specific sequences.

  • Polymerase Chain Reaction (PCR): Amplifies specific DNA sequences, creating millions of copies from minimal DNA.

  • STR (Short Tandem Repeats): One of the latest methods in DNA analysis, advantageous for being less susceptible to degradation.

  • Multiplexing: Allows for analysis of multiple STRs simultaneously, improving forensic examination accuracy.

DNA Evidence in Forensics

  • Sources of DNA: Saliva, semen, urine, hair, and tissue.

  • Factors Affecting DNA Quality: Environmental factors such as moisture, heat, and time can degrade DNA.

  • CODIS: A computerized database that stores DNA profiles for comparison in criminal investigations.

  • Mitochondrial DNA: Can be used for maternal lineage tracing, time consuming but valuable for certain cases.

Evidence Collection Best Practices

  • Prior to collection:

    • Photograph and record evidence.

    • Use gloves and change frequently to avoid contamination.

  • Packaging:

    • Do not store biological evidence in plastic bags due to moisture retention.

    • Avoid sunlight exposure and unnecessary handling during collection.