Answer to Question #180306 in Genetics for Kenichi

Question

A local hospital has informed a family that some of the children may have been mixed up with children from other families when they were born. The hospital obtained the blood types of everyone in the family, including the surviving maternal grandfather and paternal grandmother, to rule out any possible mix-ups. The following were the outcomes:

Father: Type O Mother: Type A

1st child: Type O 2nd child: Type A

3rd child: Type B Mom's father: Type AB

Dad's mother: Type B

Answer 1

The blood group is inherited by three alleles: iA, iB and iO

The father's blood group is O and genotype is iOiO. The paternal grandmother passes iO allele to the father.

The mother blood group is A and her genotype is iAiO. Because the child have O blood group. This is possible only when the genotype of mother is iAiO. Maternal grandmother passes iA allele to the mother.

Parents: iAiO (mother) × iOiO ( father)

Punnet square:

As you seen that there is found child 1 ( O blood group) and child 2 have A blood group.

The results are also seen in the punnet square.

That's why the third child can't be the child of parents.

Hence child 3 is not the biological offspring of parents.