Summary of Blood Evidence- Lesson 1 (Forensics)

Summary of "Blood Evidence - Lesson 1 (Forensics)"

This lesson introduces forensic students to the topic of blood evidence within forensic science, focusing primarily on Forensic Serology and Blood Typing. It outlines the significance of Forensic Serology in crime solving, explains the types of tests used to identify blood at crime scenes, and provides an overview of Blood Typing as a tool in forensic investigations.

Main Ideas and Concepts

• Introduction to Forensic Serology:
  • Forensic Serology is a critical branch of forensic investigation, often more pivotal than fingerprints or hair analysis.
  • It involves laboratory tests that analyze blood serum and other bodily fluids through chemical reactions.
  • When combined with DNA analysis, Forensic Serology can provide conclusive evidence linking suspects to crime scenes.
  • Forensic Serology labs have various divisions, including Blood Typing, unknown blood characterization, blood spatter pattern analysis, paternity testing, semen identification, and DNA Profiling.
• Three Key Questions at a Crime Scene Involving Blood:
  1. Is this actually blood?
     • Investigators use Presumptive Blood Tests on-site to quickly determine if a substance is blood.
     • These tests are qualitative and rely on chemical reactions.
     • Examples:
       • Castellani’s (Castle Mayor) test: Uses phenolphthalein reagent reacting with hemoglobin to produce a bright magenta/pink color indicating blood presence.
       • Luminol Test: Used to detect latent (invisible) blood stains by causing them to glow (bioluminescence) in the presence of iron in hemoglobin, especially useful on cleaned crime scenes.
  2. Is the blood human?
     • Once blood is confirmed, further tests determine if it is human blood.
  3. What is the blood type?
     • Blood Typing is used to classify blood into groups.
     • It is a form of class evidence and cannot identify a single suspect but can help narrow down or exclude suspects.
     • Blood Typing is faster and cheaper than DNA Profiling and useful for preliminary investigations.
• Blood Typing Overview:
  • There are four main blood types: A, B, AB, and O.
  • Including the Rh factor (positive or negative), there are eight possible blood types: A+, A-, B+, B-, AB+, AB-, O+, O-.
  • Blood Typing can assist in victim/suspect elimination or confirmation.
  • The lesson includes a chart showing blood donation compatibility based on blood types.
• Additional Resources:
  • The instructor recommends a SciShow video on YouTube titled "What Are Blood Types?" for students needing further explanation.

Methodology / Instructions Highlighted

• Presumptive Blood Testing Procedure:
  • Use on-scene chemical tests (e.g., Castle Mayor test) to detect blood.
  • Apply reagent to suspected sample.
  • Observe color change (bright pink/magenta) or bioluminescence (with luminol) to confirm presence of blood.
• Blood Typing Application:
  • Use Blood Typing to classify blood samples quickly.
  • Apply Blood Typing results to narrow suspect pool or confirm victim blood.
  • Send samples for DNA analysis for definitive identification.

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Speakers / Sources Featured

• Primary Speaker: Forensic instructor/lecturer (unnamed) delivering the lesson.
• Referenced Source: SciShow (YouTube channel) – recommended for further information on blood types.

This lesson lays the foundation for understanding blood evidence in forensic science, emphasizing the importance of serology, the use of presumptive tests at crime scenes, and the utility of Blood Typing in investigations. Future lessons will cover blood spatter analysis and the physics of blood movement.

Category

Educational

Video