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 given that the mother has blood group A and the son has blood group B, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Genotypes of the Blood Groups**:
- The mother's blood group A can have the following genotypes:
- IA IA (homozygous)
- IA IO (heterozygous)
- The son's blood group B can have the following genotypes:
- IB IB (homozygous)
- IB IO (heterozygous)

2. **Determine Possible Combinations**:
- Since the son has blood group B, he must have inherited the IB allele. Therefore, the father must contribute the IB allele to the son.
- The possible combinations for the mother (A) and father (unknown) to produce a son with blood group B must be analyzed.

3. **Cross the Possible Genotypes**:
- If the mother is IA IO (heterozygous A):
- Possible combinations with the father:
- If the father is IB IB (homozygous B), the offspring could be:
- IA IB (blood group AB)
- IA IO (blood group A)
- IB IO (blood group B) - **This is a valid combination**.
- If the father is IB IO (heterozygous B), the offspring could be:
- IA IB (blood group AB)
- IA IO (blood group A)
- IB IO (blood group B) - **This is also a valid combination**.
- If the mother is IA IA (homozygous A):
- Possible combinations with the father:
- If the father is IB IB (homozygous B), the offspring could only be:
- IA IB (blood group AB) - **Not valid**.
- If the father is IB IO (heterozygous B), the offspring could only be:
- IA IB (blood group AB) - **Not valid**.
- Therefore, the mother cannot be IA IA.

4. **Conclusion**:
- Since the mother must be IA IO (heterozygous A) and the father must contribute the IB allele, the possible blood group of the father is **B** (either IB IB or IB IO).

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

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