A man with blood group A marries a woman with blood group O and their daughter has blood group O.Is this information enough to tell you which of the traits --blood group A or O is dominant ?Why or Why not ?

This information is not sufficient to determine which of the traits − blood group A or O − is dominant. This is because we do not know about the blood group of all the progeny.

Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.The blood group in human body is classified not only on the basis of the Genes but also according to the presence of Antigen & Antibody present in the blood.

The blod group of daughter would be similar to mother depending upon some other factors also...So, the given information is not enough in this case.