Question

The toxin proteins isolated from {Bacillus thuringiensis, coded by which of the following genes would control cotton bollworms and corn borer, respectively ?}

• A. {cryIAc} and {cryIAb}
• B. {cryIIAb} and {cryIAc}
• C. {cryIAc} and {cryIIAb}
• D. {cryIAc} and {cryIIAb}

Hint:

Logic Tip: Pay close attention to the small letters! \textbf{A}c and II\textbf{A}b = Cotton. I\textbf{A}b = Corn. Don't let similar-looking gene names trick you during the exam.

Answer 1

The Correct Option is A

Step 1 : Understanding the Question:
The question asks to identify the specific {cry} genes from the bacterium {Bacillus thuringiensis} (Bt) that encode toxins for two different agricultural pests: cotton bollworms and the corn borer. The answer must be provided in the correct "respective" order as stated in the prompt.
Step 2 : Key Formulas and Approach:
The toxin proteins produced by Bt are insect-group specific. The genes are named "cry" followed by identifiers.
1. Target: Cotton Bollworm $\rightarrow$ Genes involved: {cryIAc} and {cryIIAb}.
2. Target: Corn Borer $\rightarrow$ Gene involved: {cryIAb}.
3. Methodology: Match the gene for Cotton first and the gene for Corn second.
Step 3 : Detailed Explanation:

Bacillus thuringiensis (Bt): This soil bacterium produces crystalline protein inclusions that are toxic to specific insect larvae (Lepidopterans, Coleopterans, and Dipterans). Biotechnologists have inserted these genes into crops to make them pest-resistant.

Cotton Bollworm Control: Extensive agricultural research has shown that the proteins encoded by the genes {cryIAc} and {cryIIAb} are highly effective at controlling cotton bollworms. These are the primary genes found in commercial Bt Cotton.

Corn Borer Control: The corn borer ({Ostrinia nubilalis}) is susceptible to a slightly different crystalline toxin. The gene coding for the protein that specifically targets the corn borer is {cryIAb}. This gene is utilized in the production of Bt Corn.

Sequential Logic: The question specifies "cotton bollworms" first and "corn borer" second. Therefore, the answer pair must start with a cotton gene (like {cryIAc}) and end with the corn gene ({cryIAb}).

Step 4 : Final Answer:
The combination of {cryIAc} (for cotton bollworm) and {cryIAb} (for corn borer) is the correct respective pair. This corresponds to the sequence in option (A).