Blood Groups
Your blood group is identified by the antigens and antibodies that are present in the blood. Antigens and antibodies are your blood's natural defense against foreign substances.
Antigens are protein molecules that are found on the surface of red blood cells and antibodies are found in the plasma. They recognize anything unusual in your body and alert your immune system so that it can destroy it.
The ABO system
Blood groups are defined by the ABO system. All humans and many other primates can be typed for the ABO blood group. There are four principal types: A, B, AB, and O. There are two antigens and two antibodies that are mostly responsible for the ABO types. The specific combination of these four components determines an individual's type in most cases.
Blood Group A
Blood group A has A antigens on its red blood cells and anti-B antibodies in its plasma.
For example, people with type A blood will have the A antigen on the surface of their red cells (as shown in the table below). As a result, anti-A antibodies will not be produced by them because they would cause the destruction of their own blood. However, if B type blood is injected into their systems, anti-B antibodies in their plasma will recognize it as alien and burst or agglutinate the introduced red cells in order to cleanse the blood of alien protein.
Blood Group B
Blood group B has B antigens and anti-A antibodies in its plasma.
For example, people with type B blood will have the B antigen on the surface of their red cells (as shown in the table below). As a result, anti-B antibodies will not be produced by them because they would cause the destruction of their own blood. However, if A type blood is injected into their systems, anti-A antibodies in their plasma will recognize it as alien and burst or agglutinate the introduced red cells in order to cleanse the blood of alien protein.
Blood Group AB
Blood Group AB has both A and B antigens but no antibodies, otherwise it would destroy itself.
Those who have type AB blood do not make any ABO antibodies. Their blood does not discriminate against any other ABO type. Consequently, they are universal receivers for transfusions, but their blood will be agglutinated when given to people with every other type because they produce both kinds of antigens.
Blood Group O
Blood group O has no antigens but both anti-A and anti-B antibodies. This means that group O red cells can safely be given to anyone. Individuals with type O blood do not produce ABO antigens. Therefore, their blood normally will not be rejected when it is given to others with different ABO types. As a result, type O people are universal donors for transfusions, but they can receive only type O blood themselves.
The RH System
Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it is absent, you are RhD negative. This means that you can be one of eight blood groups:
Your blood group is identified by the antigens and antibodies that are present in the blood. Antigens and antibodies are your blood's natural defense against foreign substances.
Antigens are protein molecules that are found on the surface of red blood cells and antibodies are found in the plasma. They recognize anything unusual in your body and alert your immune system so that it can destroy it.
The ABO system
Blood groups are defined by the ABO system. All humans and many other primates can be typed for the ABO blood group. There are four principal types: A, B, AB, and O. There are two antigens and two antibodies that are mostly responsible for the ABO types. The specific combination of these four components determines an individual's type in most cases.
Blood Group A
Blood group A has A antigens on its red blood cells and anti-B antibodies in its plasma.
For example, people with type A blood will have the A antigen on the surface of their red cells (as shown in the table below). As a result, anti-A antibodies will not be produced by them because they would cause the destruction of their own blood. However, if B type blood is injected into their systems, anti-B antibodies in their plasma will recognize it as alien and burst or agglutinate the introduced red cells in order to cleanse the blood of alien protein.
Blood Group B
Blood group B has B antigens and anti-A antibodies in its plasma.
For example, people with type B blood will have the B antigen on the surface of their red cells (as shown in the table below). As a result, anti-B antibodies will not be produced by them because they would cause the destruction of their own blood. However, if A type blood is injected into their systems, anti-A antibodies in their plasma will recognize it as alien and burst or agglutinate the introduced red cells in order to cleanse the blood of alien protein.
Blood Group AB
Blood Group AB has both A and B antigens but no antibodies, otherwise it would destroy itself.
Those who have type AB blood do not make any ABO antibodies. Their blood does not discriminate against any other ABO type. Consequently, they are universal receivers for transfusions, but their blood will be agglutinated when given to people with every other type because they produce both kinds of antigens.
Blood Group O
Blood group O has no antigens but both anti-A and anti-B antibodies. This means that group O red cells can safely be given to anyone. Individuals with type O blood do not produce ABO antigens. Therefore, their blood normally will not be rejected when it is given to others with different ABO types. As a result, type O people are universal donors for transfusions, but they can receive only type O blood themselves.
The RH System
Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it is absent, you are RhD negative. This means that you can be one of eight blood groups:
- A RhD positive (A+)
- A RhD negative (A-)
- B RhD positive (B+)
- B RhD negative (B-)
- RhD positive (O+)
- RhD negative (O-)
- AB RhD positive (AB+)
- AB RhD negative (AB-)
Genetic Inheritance Patterns
ABO blood types are inherited through genes on chromosome 9, and they do not change as a result of environmental influences during life. An individual's ABO type is determined by the inheritance of 1 of 3 alleles (A, B, or O) from each parent. The possible outcomes are shown below:
Parent alleles A B O
A AA(A) AB(AB) AO(A)
B AB(AB) BB(B) BO(B)
O AO(A) BO(B) OO(O)
Both A and B alleles are dominant over O. As a result, individuals who have an AO genotype will have an A phenotype. People who are type O have OO genotypes. In other words, they inherited a recessive O allele from both parents. The A and B alleles are codominant. Therefore, if an A is inherited from one parent and a B from the other, the phenotype will be AB. Agglutination tests will show that these individuals have the characteristics of both type A and type B blood.
CAUTION: The inheritance of ABO blood types does not always follow such straightforward rules of inheritance.
ABO blood types are inherited through genes on chromosome 9, and they do not change as a result of environmental influences during life. An individual's ABO type is determined by the inheritance of 1 of 3 alleles (A, B, or O) from each parent. The possible outcomes are shown below:
Parent alleles A B O
A AA(A) AB(AB) AO(A)
B AB(AB) BB(B) BO(B)
O AO(A) BO(B) OO(O)
Both A and B alleles are dominant over O. As a result, individuals who have an AO genotype will have an A phenotype. People who are type O have OO genotypes. In other words, they inherited a recessive O allele from both parents. The A and B alleles are codominant. Therefore, if an A is inherited from one parent and a B from the other, the phenotype will be AB. Agglutination tests will show that these individuals have the characteristics of both type A and type B blood.
CAUTION: The inheritance of ABO blood types does not always follow such straightforward rules of inheritance.