Question

cry genes for Bt cotton are obtained from:

• A. Tobacco mosaic virus
• B. Bottle gourd
• C. Bacillus thuringiensis
• D. Cotton plant

Hint:

Bt = Bacillus thuringiensis.
*cry* genes encode crystal proteins that act as specific endotoxins against lepidopteran, coleopteran, and dipteran insect pests.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the source organism from which the insecticidal *cry* genes expressed in transgenic Bt cotton are isolated.

Step 2: Key Formula or Approach:
Genetic engineering transfers insecticidal endotoxin-encoding genes from soil bacteria into crop plants to grant resistance against target insect pests.

Step 3: Detailed Explation:

• Origin of *cry* Genes: *cry* genes encode crystalline (Cry) endotoxin proteins produced turally by the Gram-positive soil bacterium Bacillus thuringiensis (hence abbreviated as 'Bt').

• Mechanism of Action: Upon ingestion by susceptible insects (such as the cotton bollworm, *Helicoverpa armigera*), ictive protoxins are solubilized in the alkaline gut environment and cleaved by proteases into active toxins.

• Pore Formation: Active Cry toxins bind to specific receptors on midgut epithelial cells, forming pores that lead to cell lysis, gut perforation, starvation, and death of the pest.

• Transgenic Application: Genes such as *cry1Ac* and *cry2Ab* isolated from Bacillus thuringiensis were engineered into cotton plants to create pest-resistant transgenic Bt cotton.

Step 4: Fil Answer:
The *cry* genes utilized in transgenic Bt cotton are obtained from the bacterium Bacillus thuringiensis.