Type B and B have a child who may have B blood or O blood.
If both parents of blood type B have the genotype BB, then the genotype of the child born can only be BB, and the child must be blood type B, not O.
If the parents of a B blood type have the genotype BB and BO, then the child’s genotype must also be B, and it cannot be O.
If both parents of blood type B have the genotype BO, in this case there is a 75% chance that the child will have blood type B and a 25% chance that the child will have blood type O.
If there is a need for a blood transfusion, it is recommended that patients with blood type B should be transfused with homozygous blood, and a crossover test should always be done before transfusion.