Q: If the mother’s blood group is A+ and the father’s blood group is B+; can the child’s blood group be A1+?

A:A and B (& H) are antigens (proteins) found on the surface of red blood cells (and some other tissues). The ability to form these antigens is governed by genes inherited from parents. The pattern of genes we have is called genotype and the form in, which they are expressed is called phenotype. It is the genotype (genetic make-up), which decides what the blood group (phenotype) will be. There are four possible blood groups in the ABO system: AB, A, B and O. Blood group A individuals possess A antigen on their red cells and have naturally occurring antibodies (anti-B) in their serum that react with group B and AB people. Blood group B individuals possess B antigen on their red cells and have naturally occurring antibodies (anti-A) in the serum that react with group A and AB people. Individuals with group AB possess both A and B antigens on their red cells and produce no naturally occurring antibodies. Finally, individuals with group O have neither A or B antigens on their red cells and have naturally occurring antibodies (anti- A and anti - B) in their serum that react with red cells from group A, B and AB people. In the ABO system there are three alleles (one member of a pair or series of genes that occupy a specific position on a specific chromosome): Ia - producing the antigen A, Ib - producing the antigen B and Io - producing neither antigen. IA and IB are co-dominant i.e. if both alleles are present, both antigens (A and B) will be formed on the surfaces of red blood cells and the individual will have blood group AB. Io is recessive and produces neither antigen and thus an individual will have blood group O if two of these alleles are present. The genotypic make-up can have 6 possibilities resulting in the following phenotypes: Ia Ib - AB, Ia Ia - A, Ia Io - A, Ib Ib - B, Ib Io - B, Io Io – O If either parent has group AB it will not be possible for any of the children to inherit Group O. If both parents have group O, all their children must have Group O and if both parents belong to blood group A (or B), it is still possible for some of their children to have Group O.