ABO BLOOD GROUP
ABO blood group system was discovered in 1901 by Karl Landsteiner of the University of Vienna. Later he was
awarded a Nobel Prize. ABO
blood groups are found in all humans and in many primates such as apes,
chimpanzees, baboons and gorillas.
Genetic Basis
The
ABO blood groups are controlled by Gene I
located on the chromosome 9. Gene I has
three allelic forms i.e. IA , IB
and i. The IA and IB
alleles each encode a glycosyltransferase that catalyzes the A and B antigen synthesis, respectively. The O or
i allele encodes an inactive
glycosyltransferase that leaves the ABO antigen precursor (the H antigen)
unmodified.
|
Blood type
|
Antigen on RBC
|
Allele for Antigen
|
Possible Genotypes
|
Dominance relation
|
|
Type A
|
Antigen A
|
IA
|
IA IA
, IAi
|
IA Dominant to i
|
|
Type B
|
Antigen B
|
IB
|
IB IB
, IBi
|
IB Dominant to i
|
|
Type AB
|
Antigen A & B
|
IA and IB
|
IA IB
|
IA and IB Co-Dominant
|
|
Type O
|
None
|
I
|
ii
|
i is recessive
|
Antigen A and Antigen B
The A and B antigens are sugars that are bound to membrane lipid molecules (fatty acids) of the red blood cell. The specificity of the A and B antigens is based on the terminal sugar.
Antigen A and B are produced by adding a specific terminal sugar to the H substance. The H substance itself contains three sugar molecules—galactose (Gal), N-acetylglucosamine (AcGluNH), and fucose.
The IA allele is responsible for an enzyme that can add the terminal sugar N-acetylgalactosamine (AcGalNH) to the H substance. The IB allele is responsible for an enzyme that can add a terminal galactose. Heterozygotes (IAIB) add either one or the other sugar to the H substance. Persons of type O (ii) cannot add either terminal sugar; these persons have only the H substance protruding from the surface of their red blood cells.
Blood group types
A
person’s blood group may be one of four types: A, B, AB, or O. These blood
group types are due to the presence of antigen A and antigen B on the surface
of RBC. A person having antigen a on the surface of RBC will have blood group
A, having antigen B on the surface of RBC will have blood group B, and having both
A and B antigens will have blood group AB. When no antigen is expressed (nor A or B), then the blood group is said to be the O blood group.
Ability to produce Antibodies against antigen A and Antigen B
The blood group is determined by antigens present on the surface of RBCs. The immune
system can produce antibodies against the foreign antigens. In
normal conditions, the body does not produce antibodies against the body's cells but can produce against any foreign agent that enters into the body.
Blood group A: An
individual with blood group A has antigen A on the RBC surface, therefore,
it only produces Antibodies against antigen B.
Blood group B: A person having blood group B
produces antibodies against the antigen A.
Blood group O: A person having no antigen A or B on the surface of RBC (Blood group O) produces anti-A and anti-B antibodies.
Blood group AB: Those who have
AB blood group do not produce antibodies.
Universal donor:
Blood type O has no antigen; therefore, a
person with blood group O can
donate the blood to all blood types.
Universal
recipient:
A person with blood type AB does not produce anti-A and anti-B
antibodies and therefore can transfuse blood from all blood types.
Other blood
group systems: Besides the
ABO blood group system there are also some other blood group systems i.e. Rh,
MNS, P, Lutheran, Kell, Lewis, secretor, Duffy, Kidd, Diago, etc.
learn more about
Multiple Alleles
Rh blood group system
Rh Blood Group system
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