3. 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?
Next: 4. How is the sex of the child determined in human beings?
Blood groups show multiple-allelism; there are three alleles A, B and O. Alleles A and B mutually expresses themselves when presenting together. We call this as co-dominance. Allele A and B show dominance only over allele O.