Question

A baby's blood group was determined as O, Rh negative. Select the blood group the baby's mother or father will not have:

• A. A, Rh Positive
• B. B, Rh Positive
• C. AB, Rh Negative
• D. O, Rh positive

Hint:

An AB parent has no hidden O gene to give an O group child.

Answer 1

The Correct Option is C

This question is about how ABO and Rh blood groups pass from parents to a child, and specifically which combination cannot exist in a parent of an O, Rh negative baby.

1. A, Rh Positive: An A group person can be genotype AO, which carries a hidden O gene. Combined with a Dd genotype for Rh, this parent can pass both O and d to the child. Possible.
2. B, Rh Positive: In the same way, a B group person can be genotype BO, carrying a hidden O, and Dd for Rh. This parent can also pass O and d. Possible.
3. AB, Rh Negative: A person with blood group AB always has the genotype AB, one A gene and one B gene, with no O gene present at all. Such a parent can never give an O gene to a child, so this parent cannot have an O group baby, whatever the Rh status is. Not possible.
4. O, Rh positive: An O group person is always genotype OO, so they always carry O, and if Rh positive as Dd, they can pass d too. Possible.

Since the baby is blood group O, both parents must carry a hidden O gene, and AB parents never carry one. So AB, Rh negative is the group the parent cannot have.

Let's summarize:

• Only genotypes AO, BO, or OO can pass an O gene, never AB.
• An O group baby always needs an O gene from each parent, ruling out AB parents entirely.

So the correct answer is AB, Rh negative.