What are the possible genotypes of the parents if a child has type O blood and the father has type A blood while the mother has type B blood?

• A. AA and BB
• B. AO and BO
• C. AB and OO
• D. OO and OO

Answer: (B)

The child's type O blood indicates a specific genotype, which must be homozygous recessive (OO). For this to occur, both parents must contribute an O allele.

In this scenario, the father with type A blood can have either genotype AA (homozygous) or AO (heterozygous). If he has AO, he can contribute an O allele to the child. The mother with type B blood can similarly be either BB (homozygous) or BO (heterozygous). If she is BO, she can also contribute an O allele.

The only combination that allows for the child to inherit an O from both parents is if both parents have those heterozygous conditions. Thus, the parents must be AO and BO, giving rise to the possibility of producing a child with type O blood through the inheritance of an O allele from each.

This reasoning supports the conclusion that the correct answer is the combination of AO and BO genetic profiles for the parents, allowing for the presence of type O blood in their child.