There are four main blood groups in humans: A, B, AB, and O. These blood groups are determined by the presence or absence of certain antigens on the surface of the red blood cells.
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Blood group A: This blood group has A antigens on the surface of the red blood cells and has anti-B antibodies in the plasma.
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Blood group B: This blood group has B antigens on the surface of the red blood cells and has anti-A antibodies in the plasma.
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Blood group AB: The AB blood group is one of the four main blood groups in humans. Individuals with the AB blood group have both A and B antigens on the surface of their red blood cells, and do not have anti-A or anti-B antibodies in their plasma.
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Blood group O: This blood group has neither A nor B antigens on the surface of the red blood cells and has both anti-A and anti-B antibodies in the plasma.
In addition to these main blood groups, there is also the Rh factor which is another antigen present on the surface of red blood cells. A person is said to be Rh positive if they have this antigen and Rh negative if they don't. So, blood groups can be further classified into Rh positive and Rh negative categories.
And the rarest blood group type is AB negative.
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