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 baby's blood group was determined as O, Rh negative. Select the blood group the baby's mother or father will not have:
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An AB parent has no hidden O gene to give an O group child.
Updated On: Jul 8, 2026
- A, Rh Positive
- B, Rh Positive
- AB, Rh Negative
- O, Rh positive
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Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Question:
The baby's blood group is O and Rh negative. We need to find which listed blood group is impossible for either parent to have, based on how ABO and Rh genes are passed down.
Step 2: Key Formula or Approach:
The ABO gene has three forms: A, B, and O, where A and B are dominant and O is recessive. A person's blood group only shows as O if both copies of the gene are O, written OO, since there is no O version to hide behind. For a child to be group O, both parents must be able to pass an O gene, so each parent's genotype must contain at least one O, meaning AO, BO, or OO, never AB. The Rh gene works the same way: Rh positive is dominant, written D, and Rh negative is recessive, written d. A child who is Rh negative must get a d from each parent, so each parent must carry at least one d, meaning DD is not possible in a parent of an Rh negative child, but Dd or dd both work.
Step 3: Detailed Explanation:
Option A, Rh Positive: this parent could be genotype AO for ABO, passing the O to the baby, and Dd for Rh, passing the d to the baby. This is possible.
Option B, Rh Positive: by the same reasoning, genotype BO and Dd works and passes both O and d. This is possible.
Option O, Rh positive: genotype OO for ABO definitely carries O, and Dd for Rh carries d. This is possible.
Option AB, Rh Negative: the AB blood group genotype is always AB, since a person needs one A gene and one B gene to show both on the surface, and there is no room for an O gene in this genotype. An AB parent can never pass an O gene to a child, no matter what the Rh status is. Since the baby is blood group O, at least one O gene must come from each parent, so an AB parent is impossible on ABO grounds alone.
Step 4: Final Answer:
The parent cannot be blood group AB, Rh negative, because an AB genotype has no O gene to pass to an O group baby.
The baby's blood group is O and Rh negative. We need to find which listed blood group is impossible for either parent to have, based on how ABO and Rh genes are passed down.
Step 2: Key Formula or Approach:
The ABO gene has three forms: A, B, and O, where A and B are dominant and O is recessive. A person's blood group only shows as O if both copies of the gene are O, written OO, since there is no O version to hide behind. For a child to be group O, both parents must be able to pass an O gene, so each parent's genotype must contain at least one O, meaning AO, BO, or OO, never AB. The Rh gene works the same way: Rh positive is dominant, written D, and Rh negative is recessive, written d. A child who is Rh negative must get a d from each parent, so each parent must carry at least one d, meaning DD is not possible in a parent of an Rh negative child, but Dd or dd both work.
Step 3: Detailed Explanation:
Option A, Rh Positive: this parent could be genotype AO for ABO, passing the O to the baby, and Dd for Rh, passing the d to the baby. This is possible.
Option B, Rh Positive: by the same reasoning, genotype BO and Dd works and passes both O and d. This is possible.
Option O, Rh positive: genotype OO for ABO definitely carries O, and Dd for Rh carries d. This is possible.
Option AB, Rh Negative: the AB blood group genotype is always AB, since a person needs one A gene and one B gene to show both on the surface, and there is no room for an O gene in this genotype. An AB parent can never pass an O gene to a child, no matter what the Rh status is. Since the baby is blood group O, at least one O gene must come from each parent, so an AB parent is impossible on ABO grounds alone.
Step 4: Final Answer:
The parent cannot be blood group AB, Rh negative, because an AB genotype has no O gene to pass to an O group baby.
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