Consider the following statements.
I) Specific Bt toxin genes have been isolated from Bacillus thuringiensis.
II) Bt toxin is coded by a gene named cry.
III) Bt toxin protein exists as inactive protoxins.
Which of the statements given above are correct?

Options

A. I, II and III
B. I and II
C. I and III
D. II and III

Answer

To determine which statements about Bt toxin and its genes are correct, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement I: Specific Bt toxin genes have been isolated from Bacillus thuringiensis.**
- **Analysis**: Bacillus thuringiensis (Bt) is a bacterium known for producing proteins that are toxic to certain insects. Specific genes that code for these toxins, known as cry genes, have indeed been isolated from this bacterium. Therefore, this statement is **correct**.

2. **Statement II: Bt toxin is coded by a gene named cry.**
- **Analysis**: The proteins produced by Bacillus thuringiensis that are toxic to insects are encoded by a family of genes known as cry genes (e.g., cry1, cry2). Thus, this statement is also **correct**.

3. **Statement III: Bt toxin protein exists as inactive protoxins.**
- **Analysis**: The Bt toxin is produced in an inactive form known as a protoxin. It is only converted into its active form after ingestion by the target insect, where it becomes toxic. Therefore, this statement is **correct**.

### Conclusion:
All three statements are correct.

Thus, the answer is that **all statements I, II, and III are correct**.