There are 4 main blood types A, B, AB and O. The blood you have depends on which antigen is found on the red blood cells and which antibody in plasma; we'll talk about it later. Blood type is hereditary and which one you have depends on your parents. If both parents have blood type A, the child will most likely also have blood type A. Likewise, type B and B parents will produce offspring with type B blood. However, if one parent is type A and the other type B, the child will be type AB. Ok, this is all pretty simple, but things get more complicated when we introduce blood type O. Blood types A and B are dominant genes, or “alleles” to be more precise. While the allele responsible for blood group O is recessive. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get Original Essay This means that if one parent has blood type O and the other parent has blood type A or B, the child is most likely to have blood type A or B. For someone to have blood type O, his parents must also have an O blood type. Making O blood types extremely rare because O blood type is recessive unlike its A and B counterparts. Now let's go back to what I was talking about before, for example: a blood type will have A antigens on blood cells and will have B antibodies in the plasma, the same goes for blood group B. However; AB blood types will have neither A nor B antigens on their red blood cells, and both A and B antibodies are in the plasma. Finally, blood type O has neither A nor B antigens on red blood cells, however both A and B antibodies are in the plasma. So so far we have four blood groups, A, B, AB and O. However, there are actually eight blood groups, at least within the ABO system. Those are A+, A-, B+, B-, AB+, AB-, O+, and O-. So where do the positives and negatives come from? It comes from a third type of antigen, called the Rh factor. Your blood cells either have Rh factor antigens or they don't. If the Rh factor antigens are present then you have a positive blood group, if they are not present you have a negative blood group. Rh negative blood can be given to patients with Rh negative or Rh positive blood type, providing primary blood type matches A, B or O, as we mentioned previously. However Rh positive blood will only be accepted from someone who also has Rh positive blood.