Question

A child who is blood type A has a mother who is blood type B. In a paternity suit a man is accused of being the father. He has blood type AB. Is he the father?

1) Yes
2) No
3) He cannot be excluded as the father.

Answer 1

The man with blood type AB cannot be ruled out as the father of a child with blood type A, who has a mother of blood type B.

Step-by-step explanation:

The man with blood type AB cannot be excluded as the father of a child with blood type A, whose mother has blood type B. Blood type A can be either homozygous (IAIA) or heterozygous (IAi), and a B blood type can also be either homozygous (IBIB) or heterozygous (IBi). Since both A and B are dominant alleles, a child with an A blood type can have one A allele from either a heterozygous AB father or a heterozygous BO mother.

In this case, if the man with AB blood type (genotype IAIB) is the father, and the mother has genotype IBi, their offspring could potentially have the following genotypes: IAIB (AB blood type), IAi (A blood type), IBi (B blood type). Therefore, the child having A blood type is consistent with genetics if the AB man is the father.