Susan, a mother with Type B blood, has a child with Type O blood. She claims that Craig, who has Type A blood, is the father. He
claims that he cannot possibly be the father. Further blood tests ordered by the judge reveal that Craig is AA. The judge rules thata. Susan is right and Craig must pay child support.b. Craig is right and doesn't have to pay child support.c. Susan cannot be the real mother of the child; there must have been an error made at the hospital.d. It is impossible to reach a decision based on the limited data available.
b. Craig is right and doesn't have to pay child support.
Explanation:
ABO blood group is controlled by three alleles. IA and IB are codominant to each other and both are dominant over i allele. IAIA and IAi produce A blood group. IBIB and IBi produce B blood group. ii produces O blood group.
Susan's son has O blood group so his genotype must be ii. He got one "i" allele from Susan and one "i" allele from his father. Craig's genotype is IAIA so there is no chance that he could have passed on "i" allele to Susan's son. Hence Craig is not his father and does not need to pay child support.
