There was a mixup at the maternity ward of a hospital in the

There was a mix-up at the maternity ward of a hospital in the 1940s and 4 young couples may have taken the wrong baby home. The babies are of blood type O, A, B, and AB. The parents’ phenotypes are AB x O; A x O; A x AB; and O x O. List all possible the phenotypes that the children of each couple could have, and determine which baby belongs to which couple.

Solution

The following are the possible phenotypes that the couples have, and the possible children:

Parent phenotype

Parent genotype

Offspring phenotype possible

Children belonging to the parent

AB x O

I^AI^B x I^O I^O

A or B type

Blood type B baby

A x O

I^A I^A/ I^A I^O x I^O I^O

A or O type

Blood type A baby

A x AB

I^A I^A/ I^A I^O x I^AI^B

A, B, or AB

Blood type AB baby

O x O

I^O I^O x I^O I^O

O only

Blood type O baby

Since the parents with O blood type can beget a child with O blood type only, the O baby cannot be the child of A x O parents.

The same way, the AB blood type baby can be produced by only parents of A x AB type.