Forensic Science
Serology – Blood Type Analysis
Serology - Blood Type Analysis
•Blood is perhaps most valuable evidencein forensics
–its presence links suspect and victim toone another and crime scene
Blood
•Blood = red fluid composed of:
•red cells
•white cells
•platelets
•plasma
•Each person’s blood has certain inheritedcharacteristics that distinguish it from other people’sblood.
•In early 1900s, Dr. Carl Landsteiner found fourmajor blood groups (A, B, AB, and O) based on thereactions of donor red blood cells with recipientserum
Blood
•Inherited genes determine which proteinsare produced in individual’s body
•ABO blood type determined by presenceor absence of specific proteins (antigens)on individual’s red blood cells
•In ABO blood typing, blood proteins(antigens) are called A and B proteins (orA and B antigens)
Blood
•Presence or absence of the A and Bantigens on the RBC determinesindividual’s blood type
•If contain protein A and lack protein B have type A blood
•Have protein B and lack protein A havetype B blood
•Both proteins AB blood
•Neither protein type O blood
Genetics
•Example of multiple alleles – IA , IB, i
•Demonstrates simple dominance andcodominance
•If IA i blood type A
•If IB i blood type B
•If IA IB blood type AB (example ofcodominance)
Phenotype
Genotype
Protein onRBC(antigen)
Antibodies inblood plasma
(serumantibody)
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 andanti-B sera
Blood
•Antibodies, found within plasma, distinguishparticular antigens on RBCs from others
•If foreign antigens are found, RBC eitherexperiences
–Bursting
OR
–Agglutination
•Usually it is necessary for exposure to anantigen to occur before antibodies areproduced; however, in this case the antibodiesare already present before any transfusion isattempted.
Blood
•Agglutination:
–the antibodies bind the antigens from different redcells
•Figure shows what you have to look for in ABOblood test result
•Agglutinated blood or clumps
indicate the presence of
various blood types
The ABO Blood Typing
•Based upon clumping phenomena of bloodsof mixed types
•Can isolate blood sera antibodies and use asblood typing sera
•Antibodies-b (Anti-A sera) would clump RBCcontaining A antigens
The ABO Blood Typing
•If attempt to transfuse type A blood into atype B recipient, the anti-A in the recipient’sblood will cause the A cells to agglutinate.
•The agglutinated cells will become trapped incapillaries
–After several days, they will rupture and releasebreakdown products
–These breakdown products may clog vital organssuch as the kidneys
–In extreme cases, the kidneys will fail and deathwill result
The ABO Blood Groups
•Safe transfusions can only occur when theantigenic properties of donor blood arecompatible with the recipient’s antibodies.
•Conditions are safe when both donor andrecipient belong to the same ABO blood group
•Type AB blood can receive blood from both typeA and type B due to the presence of both aantigens and B antigens (universal recipient)
•Type O can give blood to all three types due toabsence of antigens (universal donor)
–usually only done in emergency situations
Blood Typing
•The commercial availability of anti-A and anti-Bsera (blood sera containing antibodies againstthe A and B antigens respectively) allows thematching of donor and recipient, an importantrequirement of the modern blood bankingsystem.
Blood Typing Results
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
To determine blood type, analyze results fromblood typing test.
Other Blood Typing Systems
•Rh Factor
Rh Blood Group
•Has several antigen factors on surface ofRBC
•If any of antigens are present, will result inclumping
–Individual is identified as Rh positive (Rh+)
•If RBC lack Rh antigens, no clumpng willoccur
–Individual identified as Rh negative (Rh-)
Rh Blood Group
•Rh factors are inherited
•Genetically, simple dominant/recessivesituation
–Rh+ is dominant
•Antibodies for Rh (anti-Rh) don’t appearspontaneously but form due to exposure
Rh Blood Group
•If Rh-negative person receives transfusionof Rh-positive blood, recipient producesanti-Rh antibodies
•Generally, no serious consequences occurafter initial transfusion
•If 2nd Rh-positive transfusion is received,RBC likely to clump due to sensitivity toRh-positive blood (has antibodies to Rh-positive)
Rh Blood and Pregnancy
•If Rh-negative woman is pregnant with Rh-positive fetus for the first time and theirblood mixes during birth or miscarriage,mom can can produce antibodies to Rh-positive