Transcript Forensic Science - Spring Branch ISD

Forensic Science
Serology – Blood Type Analysis
Serology - Blood Type Analysis
• Blood is perhaps most valuable evidence
in forensics
– its presence links suspect and victim to
one another and crime scene
Blood
• Blood = red fluid composed of:
• red cells
• white cells
• platelets
• plasma
• Each person’s blood has certain inherited
characteristics that distinguish it from other people’s
blood.
• In early 1900s, Dr. Carl Landsteiner found four major
blood groups (A, B, AB, and O) based on the
reactions of donor red blood cells with recipient
serum
Blood
• Inherited genes determine which proteins
are produced in individual’s body
• ABO blood type determined by presence
or absence of specific proteins (antigens)
on individual’s red blood cells
• In ABO blood typing, blood proteins
(antigens) are called A and B proteins (or A
and B antigens)
Blood
• Presence or absence of the A and B
antigens on the RBC determines
individual’s blood type
• If contain protein A and lack protein B 
have type A blood
• Have protein B and lack protein A  have
type B blood
• Both proteins  AB blood
• Neither protein  type O blood
Genetics
• Example of multiple alleles – IA , IB, i
• Demonstrates simple dominance and
codominance
• If IA i  blood type A
• If IB i  blood type B
• If IA IB  blood type AB (example of
codominance)
Phenotype
Genotype
Protein on
RBC
(antigen)
Antibodies in
blood plasma
(serum
antibody)
Type A
IAIA or IAi
A
b
anti-B sera
Type B
IBIB or IBi
B
a
anti-A sera
Type AB
IAIB
A and B
---
Type O
ii
---
a and b
anti-A and
anti-B sera
Blood
• Antibodies, found within plasma, distinguish
particular antigens on RBCs from others
• If foreign antigens are found, RBC either
experiences
– Bursting
OR
– Agglutination
• Usually it is necessary for exposure to an
antigen to occur before antibodies are
produced; however, in this case the antibodies
are already present before any transfusion is
attempted.
Blood
• Agglutination:
– the antibodies bind the antigens from different red
cells
• Figure shows what you have to look for in ABO
blood test result
• Agglutinated blood or clumps
indicate the presence of
various blood types
The ABO Blood Typing
• Based upon clumping phenomena of bloods
of mixed types
• Can isolate blood sera antibodies and use as
blood typing sera
• Antibodies-b (Anti-A sera) would clump RBC
containing A antigens
The ABO Blood Typing
• If attempt to transfuse type A blood into a
type B recipient, the anti-A in the recipient’s
blood will cause the A cells to agglutinate.
• The agglutinated cells will become trapped in
capillaries
– After several days, they will rupture and release
breakdown products
– These breakdown products may clog vital organs
such as the kidneys
– In extreme cases, the kidneys will fail and death
will result
The ABO Blood Groups
• Safe transfusions can only occur when the
antigenic properties of donor blood are
compatible with the recipient’s antibodies.
• Conditions are safe when both donor and
recipient belong to the same ABO blood group
• Type AB blood can receive blood from both type
A and type B due to the presence of both a
antigens and B antigens (universal recipient)
• Type O can give blood to all three types due to
absence of antigens (universal donor)
– usually only done in emergency situations
Blood Typing
• The commercial availability of anti-A and anti-B
sera (blood sera containing antibodies against
the A and B antigens respectively) allows the
matching of donor and recipient, an important
requirement of the modern blood banking
system.
Blood Typing Results
To determine blood type, analyze results from
blood typing test.
anti-A sera + blood
anti-B sera + blood
Type A
Clumps
no clumps
Type B
no clumps
Clumps
Type AB
Clumps
Clumps
Type O
no clumps
no clumps
Other Blood Typing Systems
• Rh Factor
Rh Blood Group
• Has several antigen factors on surface of
RBC
• If any of antigens are present, will result in
clumping
– Individual is identified as Rh positive (Rh+)
• If RBC lack Rh antigens, no clumpng will
occur
– Individual identified as Rh negative (Rh-)
Rh Blood Group
• Rh factors are inherited
• Genetically, simple dominant/recessive
situation
– Rh+ is dominant
• Antibodies for Rh (anti-Rh) don’t appear
spontaneously but form due to exposure
Rh Blood Group
• If Rh-negative person receives transfusion
of Rh-positive blood, recipient produces
anti-Rh antibodies
• Generally, no serious consequences occur
after initial transfusion
• If 2nd Rh-positive transfusion is received,
RBC likely to clump due to sensitivity to
Rh-positive blood (has antibodies to Rhpositive)
Rh Blood and Pregnancy
• If Rh-negative woman is pregnant with Rhpositive fetus for the first time and their
blood mixes during birth or miscarriage,
mom can can produce antibodies to Rhpositive