A couple has a child whose blood group is different from his mother as well as his father. The possible blood group of the parents could be

Options

A. A and AB
B. B and AB
C. AB and O
D. A and O

Answer

To solve the problem of determining the possible blood groups of the parents when a couple has a child whose blood group is different from both parents, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Blood Group Genetics**:
- Blood groups are determined by the ABO blood group system, which involves three alleles: IA (A), IB (B), and IO (O).
- The A and B alleles are dominant, while the O allele is recessive.

2. **Identifying Parent Blood Groups**:
- For a child to have a blood group different from both parents, at least one parent must carry the recessive O allele (IO).
- The possible combinations of blood groups for the parents must allow for the child to inherit a different blood group.

3. **Analyzing Possible Parent Combinations**:
- **Option 1: A and AB**:
- Parent A (IA, IO) and Parent AB (IA, IB) can produce A (IA, IO), B (IB, IO), AB (IA, IB), but not O. Therefore, this option is incorrect.

- **Option 2: B and AB**:
- Parent B (IB, IO) and Parent AB (IA, IB) can produce A (IA, IO), B (IB, IO), AB (IA, IB), but not O. Therefore, this option is incorrect.

- **Option 3: AB and O**:
- Parent AB (IA, IB) and Parent O (IO, IO) can produce A (IA, IO), B (IB, IO), but not AB or O. This option is valid since the child can have blood groups A or B, which are different from both parents.

- **Option 4: A and O**:
- Parent A (IA, IO) and Parent O (IO, IO) can produce A (IA, IO) or O (IO, IO), but not B or AB. Therefore, this option is incorrect.

4. **Conclusion**:
- The only combination that allows for a child to have a blood group different from both parents is when one parent has blood group AB and the other has blood group O. Hence, the correct answer is **AB and O**.

### Final Answer:
The possible blood groups of the parents could be **AB and O**.