Question

A men with blood group A marries a women with blood group O & their daughter has blood group O .Is this informatiion enough to tell you which of the trait blood group A or O is dominant ? Why or why not?

Answer 1

A man with A blood group can have either I ^A I ^A alleles (genotype) or I ^A i alleles, woman with blood group O will have ii allele. So,women can contribute only i allele to daughter whereas the man can contribute either I ^A or i allele. The daughter have blood group A means man has contributed I ^A allele and woman i. But I A is expressing itself in the presence of i showing I ^A is dominant over i. Hence the information given in the question is enough for telling which blood group is dominant.