All the following are correct , except :

Options

A. i-gene codes for the repressor of lac operon
B. z-gene codes for the beta-galactosidase
C. y-gene codes for transacetylase
D. three gene products are required for

Answer

To solve the question "All the following are correct, except:", we need to evaluate each statement provided in the options. Let's break it down step by step.

### Step 1: Analyze the First Statement
- **Statement:** The I gene codes for the repressor of the lac operon.
- **Evaluation:** This statement is correct. The I gene indeed codes for the repressor protein, which inhibits the expression of the lac operon when lactose is not present.

### Step 2: Analyze the Second Statement
- **Statement:** The Z gene codes for beta-galactosidase.
- **Evaluation:** This statement is also correct. The Z gene is one of the structural genes in the lac operon and it encodes the enzyme beta-galactosidase, which is responsible for breaking down lactose into glucose and galactose.

### Step 3: Analyze the Third Statement
- **Statement:** The Y gene codes for transacetylase.
- **Evaluation:** This statement is incorrect. The Y gene actually codes for permease, which facilitates the transport of lactose into the cell. Transacetylase is coded by the A gene, not the Y gene.

### Step 4: Analyze the Fourth Statement
- **Statement:** Three gene products are required for lactose metabolism.
- **Evaluation:** This statement is correct. The lac operon consists of three structural genes (Z, Y, and A) that are involved in lactose metabolism.

### Conclusion
After evaluating all statements, we find that the only incorrect statement is the third one regarding the Y gene. Therefore, the answer to the question is:

**Answer:** The third statement is incorrect.

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