What determines a child’s blood group?

Monday July 29 2019

Why do we have different blood types

In olden times, blood groups were used to rule out rather than determine parenthood. 

By Vincent Karuhanga

If my wife and I are both blood group O positive, can we give birth to a child of blood group O negative?


Dear Haruna,
Yes, blood group O positive couples can get blood group O negative offspring.
We have 4 blood types A, B, AB, and O determined by a small protein on the surface of the red blood cells called an antigen. Blood group O does not have an antigen. Another kind of antigen is the Rhesus factor with its presence or absence determining whether one’s group is positive or negative. Positive people have inheritance determinants called genes + + or + - meaning that if a man and woman have the genes as + - and + - then they are likely to have a 50% chance of getting a rhesus negative offspring despite them being Rhesus positive.
Many people use blood groups for determination of parents but these not being completely reliable require to conclusively use DNA maternity or paternity tests.