A,AB and B blood groups are formed in `1:2:1` ratio by

Options

A. `I^(A)I^(O) xx I^(A) I^(B)`
B. `I^(A)I^(B) xx I^A I^(B)`
C. `I^(B) I^(O) xx I^(A) I^(B)`
D. All these

Answer

To solve the question regarding the formation of A, AB, and B blood groups in a 1:2:1 ratio, we will analyze the genetic crosses provided in the options.

### Step-by-Step Solution:

1. **Understanding Blood Group Genetics**:
- Blood groups are determined by the presence of specific antigens on the surface of red blood cells. The alleles involved are A (IA), B (IB), and O (i).
- The possible genotypes for blood groups are:
- Blood group A: Genotype AA or AO (IAIA or IAi)
- Blood group B: Genotype BB or BO (IBIB or IBi)
- Blood group AB: Genotype AB (IAIB)
- Blood group O: Genotype OO (ii)

2. **Analyzing the First Option (AO x AB)**:
- Cross: AO (Blood group A) x AB (Blood group AB)
- Possible offspring genotypes:
- AA (Blood group A)
- AO (Blood group A)
- AB (Blood group AB)
- BO (Blood group B)
- Resulting blood groups: 2 A (AA and AO), 1 AB, 1 B (BO)
- Ratio: A:AB:B = 2:1:1
- This does not match the required 1:2:1 ratio.

3. **Analyzing the Second Option (AB x AB)**:
- Cross: AB (Blood group AB) x AB (Blood group AB)
- Possible offspring genotypes:
- AA (Blood group A)
- AB (Blood group AB)
- AB (Blood group AB)
- BB (Blood group B)
- Resulting blood groups: 1 A (AA), 2 AB, 1 B (BB)
- Ratio: A:AB:B = 1:2:1
- This matches the required 1:2:1 ratio.

4. **Analyzing the Third Option (BO x AB)**:
- Cross: BO (Blood group B) x AB (Blood group AB)
- Possible offspring genotypes:
- BA (Blood group AB)
- BO (Blood group B)
- AO (Blood group A)
- AB (Blood group AB)
- Resulting blood groups: 1 A (AO), 2 AB (BA and AB), 1 B (BO)
- Ratio: A:AB:B = 1:2:1
- This also matches the required 1:2:1 ratio.

5. **Conclusion**:
- The second option (AB x AB) fulfills the requirement of producing A, AB, and B blood groups in a 1:2:1 ratio.
- Since the first option does not fulfill the requirement, the correct answer is **Option 2**.

### Final Answer:
**Option 2: AB x AB produces A, AB, and B blood groups in a 1:2:1 ratio.**