A man with blood group It IA IA is married to a woman with blood group IA IO. The blood group of their son is likely to be

Analyze the question

The question asks for the likely blood group of a child. The father's genotype is given as IA IA (the "It" in the question is a typo for IA). The mother's genotype is IA IO. This is a monohybrid-style cross on ABO inheritance.

Concept

The ABO blood group is controlled by three alleles: IA, IB and IO.

• IA and IB are codominant.
• IO is recessive to both.
• Genotypes IA IA and IA IO both give blood group A.
• IO IO gives group O.
• IB IB and IB IO give group B.
• IA IB gives group AB.

Solution

Father: IA IA, so all his gametes are IA. Mother: IA IO, so her gametes are IA or IO.

| | IA (mother) | IO (mother) | |---|---|---| | IA (father) | IA IA | IA IO |

Offspring genotypes:

• 50% IA IA, which is blood group A
• 50% IA IO, which is blood group A

So every child, including the son, will have blood group A. Groups O, B and AB are not possible, because the father can only pass on IA and neither parent carries IB.

Answer: A

Exam tip

When one parent is homozygous (IA IA), that parent only passes on IA. The child can never be O, because O needs an IO from both parents. Also check whether either parent carries IB. If neither does, groups B and AB are impossible.