Question

28.four children with blood groups A,B ,AB ,O were born to a mother with blood group B.the father had blood group A.indicate the genotype of every member of the family?

Answer 1

Blood group of the father : A
Blood group of the mother : B
Blood groups of the children : A, B, AB, O

A and B alleles are dominant over the O. ( A = B > O)

Unless and until the O gene is present in a complete homozygous state, the progeny wouldn't express the blood group O. Hence, the genotype of the blood group O child is OO.

This also indicates that each of the parents has an O allele besides a dominant A/B. (Hence, a child could get the OO genotype i.e., one O from the mother and the other O from the father)
Thence, the genotypes of the mother and the father are BO and AO respectively.

It is clear that the genotype of the child with blood group AB is AB itself.
(A from the father and B from the mother)

The genotype of the child with blood group A would be AO (and not AA) because the A comes from the father with genotype AO and the O comes from the mother with genotype BO.

Similarly, the genotype of the child with blood group B would be BO (and not BB) because the B comes from the mother with genotype BO and the O comes from the father with genotype AO.