Blood types

At first glance all blood looks equally red. Still, not every blood suits every person. For a blood transfusion, when someone receives foreign blood, it has to match their own blood type. Otherwise the body fights the foreign blood, and that is dangerous.

What tells the groups apart

On the surface of the red blood cells sit tiny markers, called antigens. There is marker A and marker B. From these come four blood groups: group A carries only A, group B only B, group AB both, and group 0 neither. Together these four form the ABO system.

Donor and recipient

Group 0 carries no markers that a foreign body could fight against. That is why group 0 can donate blood to all others and is called the universal donor. Group AB knows both markers and fights neither of them, so it can receive blood from all groups and is called the universal recipient. Besides the ABO system there is the Rhesus factor, written as plus or minus after the group, for example A positive. Strictly speaking, only blood of group 0 negative therefore suits every recipient, and only someone with AB positive tolerates blood from truly every group.

Blood types are inherited

You get your blood type from your parents. Each parent passes on one version, either A, B, or 0. A and B are stronger than 0 and win out. Someone who inherits versions A and 0 therefore has blood group A. Against each other A and B are equally strong: someone who inherits A and B shows both markers and has blood group AB. In the cross grid you can play through which groups are possible in the children.