The given information is not enough to tell us which of the traits- blood group A or O - is dominant. In blood heredity, blood type A is always dominant and blood type O is always recessive. Here, father’s blood group can be AA (homozygous) or AO (heterozygous) genotypically, where as that of mother can be OA or OO. For daughter to be born with blood group O, she must receive O type gene one each from father and mother. For this father must have heterozygous AO blood group and mother must have homozygous blood group OO.
