The humans follow the AB system and the Rh system of the blood group.

According to this, there are FOUR types of blood groups:-

A

B

AB

O

Each of these can occur in two different forms – positive or negative, depending on the presence or absence of the Rhesus antigens. B

Blood group A-

The surface of the RBCs having blood group A consists of A antigen

The plasma of such cells consists of anti – B antibodies

The presence of antigen Rhesus D will make it A+

Blood group B-

It contains anti A antibodies

Whereas it has B antigens on its surface

Blood group AB

It consists of both, A and B antigens

Whereas no antibodies are present in its plasma

These are universal recipients during blood transfusion

Blood group O-

These do not have any antigen on their surfaces

These have antibodies against all other blood groups, that is, anti A antibodies and anti B antibodies

These the universal donors during blood transfusion

The presence and absence of Rh factor marks an important role during blood transfusions. Blood of an Rh positive donor cannot be transfused to an Rh negative recipient. The reason behind this lies in the absence of Rh antigen in an Rh negative person. Due to the absence of antigens, it will form antibodies against the Rh positive blood. The blood will start to clot, which at times can be fatal.

AB+ blood group is considered to be a universal recipient-

This means that a person having AB+ blood group can receive blood from any other blood groups. Be it positive or negative, A or B or O. It can receive blood from any of them. The reason behind that is- it lacks antibodies against of the groups and has antigens of A, B and Rh+. Thus it is a universal recipient.

O negative is the universal donor-

A person having O negative blood type can donate blood to anyone. Since it lack antigens for any blood group, it will not allow the other groups to form antibodies against it – As it is free of any antigens. Thus, O negative is the universal donor.

The blood group we have depends on the genes we receive. Blood group of a child having AB and AA type of parents can never be O. Thus, blood group and its types depends on the genes we receive from our parents.