Can a father of blood group A and wife of Blood group B give birth to a son who is blood group O? Jacob
In olden times, blood groups were used to rule out rather than determine parenthood. Even in this they were not always helpful, the reason DNA testing, which is more definite has come in handy.
Blood groups are mainly classified by the ABO blood system and the Rhesus type system. The four blood groups are A, B, AB and O. Each blood group is either Rh-positive or Rh-negative. The Rhesus factor is most important when a woman becomes pregnant and the ABO for blood transfusion.
A person’s blood group is determined by a pair of genes, one each inherited from their mother and father. The blood group is determined by chemical substances called antigens located on the surfaces of red blood cells.
For a person of blood group A the pair of genes are AA or AO. For your wife who is blood group B her genes will then be BB and BO. The resultant offspring then could be OO, AO, AB or BO with OO children then being blood group O.
Also Rhesus (RhD) positive parents can get a RhD negative offspring since RhD positive parents are either + - or + +.