Q: If a father has B+ blood group, mother has A+. Is it possible to have a child with O negative blood group?

A:Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three alleles: i, IA, and IB. The gene encodes a glycosyltransferase—that is, an enzyme that modifies the carbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome (9q34).

The IA allele gives type A, IB gives type B, and i gives type O. As both IA and IB are dominant over i, only ii people have type O blood. Individuals with IAIA or IAi have type A blood, and individuals with IBIB or IBi have type B. IAIB people have both phenotypes, because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child. A type A and a type B couple can also have a type O child if they are both heterozygous (IBi,IAi).

As far as the Rh positivity is concerned, this again is dependent on the expression of Rh antigens D, C, c, E and e. A person can be heterozygous for these antigens the same way as for the above mentioned ABO blood groups. Therefore, the possibility of a child having ‘O negative blood group is very much possible.