Both husband and wife have type A blood children may have blood type A or O. Inheritance of the human blood group system is linked to the three ABO alleles on the chromosomes. Only two of the ABOs are possible on a pair of chromosomes, from the father and the mother. The three genes can form six genotypes i.e. AA, AO, BB, BO, AB, OO. A and B are dominant genes and O is recessive, so there are only four blood group expression types A, B, AB and O. The blood group expression types are A, B, AB, and O. The genotypes of people with the same blood type are not necessarily the same, and the genotype of blood type A can be AA or AO, so couples with blood type A children may have blood type A or O.