Children born to parents with blood types AB and B may have blood types AB, A or B. The ABO blood type consists of four types of blood, namely A, B, AB or O. The A and B genes are dominant. The ABO blood group consists of four blood types, namely A, B, AB or O. This type of blood type is mainly controlled by three genes, A, B and O. The A and B genes are dominant and the O gene is recessive. The chromosomes contain two single strands, and the child can get one chromosome from each parent. The two single-stranded chromosomes controlling blood type AB are the A and B genes, while blood type B contains the B and O genes. Then AB and B blood types can get 4 gene combinations by crossing over, i.e. AB, OA, OB or BB, and the child has 3 possible blood types, i.e. AB, A or B blood.