Blood group of mother is A. That of son is B. What is blood group of father

Options

A. B
B. A
C. O
D. None of the above

Answer

To determine the blood group of the father when the mother's blood group is A and the son's blood group is B, we can analyze the genetic inheritance of blood groups.

### Step-by-Step Solution:

1. **Identify the Blood Group of the Mother**:
- The mother has blood group A. Blood group A can be either homozygous (AA) or heterozygous (AO).

2. **Identify the Blood Group of the Son**:
- The son has blood group B. Blood group B can be either homozygous (BB) or heterozygous (BO).

3. **Consider the Possible Blood Groups of the Father**:
- To have a son with blood group B, the father must contribute a B allele. Therefore, the father can either have blood group B (BB or BO) or blood group AB (AB).

4. **Case 1: Mother is Homozygous (AA)**:
- If the mother is AA, she can only pass on an A allele.
- The son cannot be B if the mother is AA, as he would inherit an A from her.
- Therefore, this case is not possible.

5. **Case 2: Mother is Heterozygous (AO)**:
- If the mother is AO, she can pass on either an A or an O allele.
- For the son to be B, he must inherit a B allele from the father.
- If the father is blood group B (either BB or BO), he can provide the B allele.

6. **Crossing the Alleles**:
- If the father is BO (heterozygous B), the possible combinations from the mother (AO) and father (BO) are:
- A (from mother) + B (from father) = AB (not the son)
- A (from mother) + O (from father) = AO (A blood group)
- O (from mother) + B (from father) = BO (B blood group)
- O (from mother) + O (from father) = OO (O blood group)
- The son can be B (BO) in this case.

7. **Conclusion**:
- Therefore, the only possible blood group for the father, given that the mother is AO and the son is B, is blood group B (either BB or BO).

### Final Answer:
The blood group of the father is B.

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