Identify the wrong statement

Options

A. Alleles b and c also produce sugar
B. Alleles `I^A ` and `I^B` produce sugar
C. When `I^B` and b or I are present only `I^B` is expressed
D. Both `I^A ` and `I^B` are present together and they express because of co-dominance

Explanation

To identify the wrong statement regarding the ABO blood group system, let's analyze the statements one by one based on the information provided in the transcript.

### Step-by-Step Solution:

1. **Understanding ABO Blood Groups**: The ABO blood group system consists of four main blood types: A, B, AB, and O. These blood types are determined by the presence of specific sugar molecules (antigens) on the surface of red blood cells (RBCs), which are encoded by the I gene.

2. **Identifying the Alleles**: The alleles involved in the ABO blood group system are:
- I^A (produces A antigen)
- I^B (produces B antigen)
- i (produces no antigen, leading to blood type O)

3. **Analyzing the Statements**:
- **Statement 1**: "Alleles B and C also produce sugar."
- This statement is incorrect because there is no allele C in the ABO blood group system. The alleles are I^A, I^B, and i. Therefore, this statement is wrong.

- **Statement 2**: "Alleles I^A and I^B produce sugar."
- This statement is correct as both I^A and I^B produce specific sugars (A and B antigens, respectively).

- **Statement 3**: "When I^B and i are present, only I^B is expressed."
- This statement is correct because I^B is dominant over i, meaning that the presence of I^B will mask the expression of i.

- **Statement 4**: "Both I^A and I^B are expressed because of co-dominance."
- This statement is also correct. When both I^A and I^B are present, they express their respective antigens simultaneously, resulting in blood type AB.

4. **Conclusion**: The wrong statement is clearly identified as the first one: "Alleles B and C also produce sugar."

### Final Answer:
The wrong statement is: "Alleles B and C also produce sugar."