Blood Group Markers in Forensics

Study Notes

Blood Group Markers

There are 33 known blood group markers.
"Blood group" encompasses a system of red blood cell (RBC) antigens controlled by genes that may be allelic or closely linked on the same chromosome.
"Blood type" indicates a specific reaction pattern to antisera within a blood group system.

Importance of Blood Groups in Forensics

Blood typing can identify matches or exclusions between samples, providing critical information in criminal investigations.
Exclusion results indicate that two samples do not share a common origin.
Forensic blood typing acts as a confirmatory test and offers insights about a suspect's blood type, narrowing down potential criminals without identifying a specific individual.

ABO Blood Group System

Discovered by Karl Landsteiner in 1900, for which he won a Nobel prize.
Classified into four blood types based on:
- Presence or absence of surface antigens on RBCs.
- Plasma antibodies.
Group A: A antigen present, B antibody in plasma.
Group B: B antigen present, A antibody in plasma.
Group AB: Both A and B antigens present, no antibodies in plasma.
Group O: No A or B antigens, both A and B antibodies in plasma.

Rh Factors

Rh factor derived from studies on Rhesus monkeys, relating to a specific blood protein.
Rh positive (Rh+) indicates presence of the protein; Rh negative (Rh-) indicates absence.

Blood Typing Methodology

Blood typing involves looking for agglutination or clumping indicative of specific antigen-antibody reactions.

Bloodstain Pattern Analysis (BPA)

BPA interprets bloodstains at crime scenes to reconstruct events surrounding the bloodshed.
Analysts evaluate size, shape, distribution, and location of stains to assess actions and reconstruct the crime.
BPA incorporates biology, physics, and mathematics to answer key questions:
- Type and velocity of weapon used.
- Number of blows sustained.
- Handedness of the attacker.
- Positions and movements of victim and assailant.
- Sequence of inflicted wounds.
- Nature of injuries sustained.
- Time since crime was committed.
- Timing of death relative to the attack.

Contributions to BPA History

Eduard Piotrowski: Pioneer researcher on blood spatter (1895).
Balthazard: First to analyze blood spatter patterns meaningfully (1939).
Paul Kirk: Demonstrated positions of victim and assailant and striking methods used.
Dr. Herbert MacDonell: Published on blood flight characteristics in 1971 and founded the International Association of Bloodstain Pattern Analysts (IABPA) in 1983.

Key Terms in Bloodstain Analysis

Spatter: Bloodstains resulting from the application of force.
Origin/Source: The location where blood spatter originated.
Angle of Impact: The angle at which a blood droplet strikes a surface.
Parent Drop: The original droplet from which satellite spatters derive.
Satellite Spatters: Smaller drops that separate from the parent spatter upon impact.
Spines: Pointed edges of a stain that indicate the direction of blood travel.
Cast-off: Blood thrown from an object during movement.

Description

Explore the 33 blood group markers and their significance in forensic science. This quiz focuses on how blood groups can help establish possible matches between samples, leveraging the unique antigens present in red blood cells. Gain insights into the critical role of blood type testing in forensic investigations.