Question

If blood group of mother is B (homozygous) and that of father is A (homozygous), these blood groups are absent in their children.

• A. A, AB, B
• B. A, AB, O
• C. B, O, A
• D. AB, O, B

Hint:

When both parents are homozygous for different dominant alleles ($I^A I^A$ and $I^B I^B$), $100\%$ of the offspring will have the heterozygous codominant phenotype (AB).
This eliminates any possibility of groups A, B, or O appearing in the children.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks us to determine which blood groups will be completely absent in the offspring of a homozygous B mother and a homozygous A father.

Step 2: Key Concept and Approach:
Blood groups in humans are determined by the ABO gene, which exhibits multiple alleles: $I^A$, $I^B$, and $i$.
The alleles $I^A$ and $I^B$ are codominant, whereas $i$ is recessive.
We will find the genotypes of both parents and use a Punnett square to determine the possible genotypes and phenotypes of their children.

Step 3: Detailed Explanation:

• Parental Genotypes: Since the mother has blood group B and is homozygous, her genotype is $I^B I^B$.
Since the father has blood group A and is homozygous, his genotype is $I^A I^A$.

• Gametes Produced: The mother produces gametes containing only the $I^B$ allele, while the father produces gametes containing only the $I^A$ allele.

• Offspring Genotype: Fertilization of these gametes results in offspring with the genotype $I^A I^B$.

• Offspring Phenotype: Due to codominance between $I^A$ and $I^B$, all children will express the AB blood group.

• Absent Blood Groups: Consequently, the blood groups A, B, and O will be completely absent in their children.


Step 4: Final Answer:
The blood groups absent in their children are B, O, and A, which corresponds to Option (C).