Blood Group Markers and Forensics

Study Notes

Blood Group Markers

There are 33 recognized blood group markers in human blood.
Blood group systems reflect red blood cell (RBC) antigens controlled by genes, which can be allelic or closely linked on the same chromosome.
Blood type indicates how blood interacts with specific antisera in testing.

Importance in Forensics

Blood typing can establish matches or exclusions between two samples.
Exclusion results indicate that samples do not share a common origin, crucial for criminal investigations.
Forensic blood typing provides confirmation and aids in identifying suspects through blood type information.
While blood typing isn't definitive for individual identification, it can narrow down possible suspects.

ABO Blood Group System

Discovered by Karl Landsteiner in 1900, earning him a Nobel Prize.
Classified into four main types based on antigens and antibodies:
- Group A: A antigen present on RBC surface, B antibody in plasma.
- Group B: B antigen present on RBC surface, A antibody in plasma.
- Group AB: Both A and B antigens on RBC surface, no antibodies in plasma.
- Group O: No antigens on RBC surface, both A and B antibodies in plasma.

Rh Factors

Rh factor derived from studies on Rhesus monkeys, indicating blood protein presence.
Rh positive (Rh+) indicates the presence of the protein, while Rh negative (Rh-) indicates its absence.

Blood Typing Techniques

Blood typing focuses on identifying agglutination (clumping) patterns.

Bloodstain Pattern Analysis (BPA)

BPA interprets bloodstains at crime scenes to reconstruct events.
Analysts evaluate stain size, shape, distribution, and location for insights.
Utilizes biology, physics, and mathematics to answer investigative questions about:
- Weapon type and velocity.
- Number of blows and handedness of the assailant.
- Victim and assailant movements and positions.
- Sequence and type of injuries.
- Estimated time since the crime and death immediacy.
Supports or corroborates witness statements and medical findings, ensuring consistency in evidence.

History of Bloodstain Pattern Analysis

Eduard Piotrowski (1895): Earliest known study on blood spatters.
Balthazard (1939): First to analyze blood spatter patterns' significance.
Paul Kirk: Demonstrated victim and assailant positioning relative to blood spatter.
Dr. Herbert MacDonell (1971): Published on blood flight characteristics; established the IABPA in 1983.

Definitions of Terms

Spatter: Bloodstains resulting from force applied to a blood source.
Origin/Source: The location blood spatter originates from.
Angle of Impact: The angle at which a blood droplet strikes a surface.
Parent Drop: The main droplet from which satellite spatters emerge.
Satellite Spatters: Small blood drops that separate from the parent spatter upon impact.
Spines: Pointed edges of bloodstains indicating direction of travel.
Cast-off: Blood flung from an object during swinging motions.

Description

Explore the 33 recognized blood group markers and their implications in forensic science. This quiz delves into how blood typing can help establish matches or exclusions in criminal investigations. Understand the ABO blood group system's significance and its historical discovery.