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ABO BLOOD GROUPS
CHAPTER 4 P. 83-86
ABO Blood groups are a case of Multiple Alleles
 ABO blood groups are a case of multiple alleles where
there are three alternative alleles for one gene
 Discovered by Karl Landersteiner in the early 1900’s
 Controlled by a gene located on c-some 9.
 One combination of alleles in the ABO system exhibits
codominance.
How is the ABO blood complex determined?
 ABO phenotype is ascertained by mixing a blood
sample with antiserum containing type A or B
antibodies
 Antigen – molecule ( often a surface protein), that is
capable of elliciting the formation of antibodies
 Antibody – Protein (Immunoglobulin) produced in
response to an antigenic stimulus binds to antigen
 If the antigen is present on the surface of the person’s
red blood cells, it will react with the antibody causing
clumping or agglutination of the red blood cells
Phenotypes
 The 4 possible Phenotypes are
 A antigen ( A Phenotype)
 B antigen ( B Phenotype)
 AB (A and B antigens presentAB Phenotype)
 O (no antigensO Phenotype)
Isoagglutinogen
 The ‘I’ designation is utilized for isoagglutinogen,
another term for antigen
 IA – A blood B antibody
 I B – B Blood A Antibody
 IAB - AB Blood  No Antibodies
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Universal Recipient
 (i)IO – O Blood  A and B Antibodies present
 Universal Donor
 IA and IB behave dominantly to IO but behave
codominantly to each other
Rh Antigens
 Rh antigens were also thought to illustrate multiple
allelism
 Important because of their involvement in the
disorder Erythroblastosis fetalis
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Form of Anemia
Occurs when mother is Rh- and father is Rh+ and those factors
contribute to the allele of the fetus
This combination results in an immunological incompatibility
of the mother and the fetus
 If the fetal blood passes through a ruptured placenta
at birth and enters the maternal circulation, the
mother’s immune system will recognize the Rh
antigen from the fetal blood and build immunities
against it.
 During a second pregnancy, the antibody
concentration becomes high enough that when they
pass across the placenta into fetal circulation they
will begin to destroy the fetal blood cells – fatal to
fetus
Preventative Measures
 Rh – mothers are given anti-sera
 Destroys Rh-positive cells that may have entered the
mother’s circulatory system
 Rh Factors and blood typing reference