Which of the following cross with respect of blood groups show both multiple allelism and co-dominance in offspring

Options

A. AxA
B. BxB
C. AB xO
D. AxB

Answer

To solve the question regarding which cross with respect to blood groups shows both multiple allelism and co-dominance in offspring, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Blood Groups and Alleles**:
- Blood groups are determined by the presence of specific antigens on the surface of red blood cells. The main alleles involved are:
- **I^A** (A antigen)
- **I^B** (B antigen)
- **i** (no antigen, O blood group)
- These alleles exhibit multiple allelism since there are more than two alleles for a single trait.

2. **Identifying Co-dominance**:
- Co-dominance occurs when both alleles in a heterozygous individual contribute to the phenotype. In the case of blood groups, both A and B antigens can be expressed simultaneously in an individual with genotype I^A I^B, resulting in AB blood type.

3. **Analyzing the Given Options**:
- **Option 1: A x A (I^A I^A)**: This will not show co-dominance as both alleles are the same (I^A).
- **Option 2: B x B (I^B I^B)**: Similar to option 1, this will not show co-dominance as both alleles are the same (I^B).
- **Option 3: A x O (I^A i)**: This will show A blood type but not co-dominance since only I^A is expressed.
- **Option 4: A x B (I^A I^B)**: This cross will produce offspring with AB blood type, showing both A and B antigens. This is an example of co-dominance, as both alleles are expressed.

4. **Conclusion**:
- The only cross that demonstrates both multiple allelism and co-dominance is **Option 4: A x B**.

### Final Answer:
The correct answer is **Option 4: A x B**.

---