Q.11 The Bt toxin gene from Bacillus thuringiensis used to generate genetically modified crops
is
(A) cry (B) cro (C) cdc (D) cr

The Bt toxin gene from Bacillus thuringiensis used in genetically modified crops is cry.​

Option Analysis

Cry genes encode the insecticidal Cry proteins (Crystal proteins) naturally produced by Bacillus thuringiensis (Bt), a soil bacterium. These genes, such as cry1Ab or cry1Ac, are isolated and inserted into crop genomes (e.g., cotton, maize) to make plants produce toxins lethal to specific pests like bollworms or borers upon ingestion, while safe for humans.​

Cro refers to a DNA-binding protein from bacteriophage lambda involved in viral replication switching, unrelated to insect toxins or GM crops.​

Cdc denotes cell division cycle genes (e.g., cdc2 in yeast) that regulate cell proliferation in eukaryotes, not bacterial toxins for agriculture.​

Cr (or cre) is a recombinase enzyme from bacteriophage P1 used in genetic engineering for site-specific DNA recombination (e.g., Cre-lox system), not a Bt toxin gene.​

Introduction: Bt Toxin Gene from Bacillus thuringiensis in Genetically Modified Crops
The Bt toxin gene from Bacillus thuringiensis revolutionizes genetically modified crops by providing built-in pest resistance. Known as the cry gene, this bacterial DNA insert enables crops like Bt cotton and Bt corn to produce insecticidal proteins, reducing pesticide use and boosting yields for farmers worldwide.​​

What is Bacillus thuringiensis?

Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces crystal (Cry) proteins during sporulation. These proteins form parasporal crystals toxic to certain insects, such as lepidopteran larvae (e.g., bollworms). Farmers have used Bt as a microbial spray since the 1920s, but genetic engineering integrates Bt toxin genes directly into plants.​

Role of Cry Gene in GM Crops

Cry genes, like cry1Ac for cotton bollworms or cry1Ab for corn borers, are cloned from Bt and inserted via Agrobacterium-mediated transformation. In the plant, they express protoxins that activate in insect guts, forming pores that disrupt digestion and cause death. This targets pests without harming beneficial insects or mammals.​​

• Over 100 cry gene variants exist, each specific to insect orders (e.g., Lepidoptera, Coleoptera).

• Bt crops cover millions of hectares globally, approved in countries like India, USA, and Brazil.

Advantages of Bt Crops

• Pest control: Reduces chemical sprays by 37% on average, per studies.

• Higher yields: Increases cotton yields by 20-30% in India.

• Environmental benefits: Lowers pesticide residues and protects non-target species.​

Limitations and Concerns

Refuge strategies plant non-Bt crops nearby to delay pest resistance. Gene flow via pollen can contaminate refuges, as seen in maize studies up to 31m away. Secondary pests may emerge without broad-spectrum control.​

This technology supports sustainable agriculture, but integrated pest management remains essential for long-term success.