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 determine the possible blood groups of the parents when a couple has a child with a different blood group than either parent, we need to analyze the genetics of blood group inheritance.

### Step-by-Step Solution:

1. **Understanding Blood Groups**: Blood groups are determined by the presence of specific antigens on the surface of red blood cells. The main blood group alleles are A (IA), B (IB), and O (i). The A and B alleles are co-dominant, meaning if both are present, both will be expressed, resulting in blood group AB. The O allele is recessive.

2. **Possible Blood Group Combinations**:
- If both parents have blood group A (IAi) and blood group O (ii), the possible offspring blood groups are A (IAi) or O (ii).
- If one parent has blood group B (IBi) and the other has blood group O (ii), the possible offspring blood groups are B (IBi) or O (ii).
- If one parent has blood group AB (IAIB) and the other has blood group O (ii), the possible offspring blood groups are A (IAi) or B (IBi).

3. **Child's Blood Group Different from Parents**: The child has a blood group that is different from both parents. This means that neither parent can have the same blood group as the child.

4. **Analyzing the Options**:
- **Option A (A and AB)**: Possible offspring blood groups are A or AB, not different.
- **Option B (B and AB)**: Possible offspring blood groups are B or AB, not different.
- **Option C (A, B, and O)**: Possible offspring blood groups are A, B, or O, which could be the same as the parents.
- **Option D (A and O)**: Possible offspring blood groups are A or O, not different.

5. **Conclusion**: The only combination that allows for a child to have a different blood group than both parents is when one parent has blood group AB and the other has blood group O. The child could then have either blood group A or B, which are different from both parents.

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