The Bt toxin gene from Bacillus thuringiensis used to generate genetically modified crops is
- (A)
cry
- (B)
cro
- (C)
cdc
- (D)
cre
GATE 2019 BT Q.1: solution and answer
Answer and solution
ANSWER
The Bt toxin gene is cry, so the answer is (A).
Official answer: ASource: Official answer key, GATE 2019 BT (IIT Madras)
The Bt toxin is the crystal (Cry) protein, a delta-endotoxin made by Bacillus thuringiensis as parasporal crystals. The gene that encodes it is named cry.
Option (A) cry: correct. The cry gene is expressed in plants such as Bt cotton and Bt brinjal. It gives insect resistance because the protoxin is activated in the alkaline insect midgut and the active toxin binds gut receptors.
Option (B) cro: wrong. cro encodes the Cro repressor of bacteriophage lambda, which acts in the lytic-lysogenic switch.
Option (C) cdc: wrong. The cdc genes are cell division cycle genes of yeast and other eukaryotes. They control cell-cycle progression.
Option (D) cre: wrong. cre encodes Cre recombinase of bacteriophage P1, which acts at loxP sites. It is used in genetic engineering to excise or invert DNA, not to confer insect resistance.
KEY IDEA
Bt toxin is the Cry (crystal) protein, a delta-endotoxin of Bacillus thuringiensis, and its gene is cry. Expressed in crops, it protects them against certain insects.
WATCH OUT FOR
Picking cre or cro because the three-letter names look alike. cre is the P1 recombinase gene and cro is a lambda phage repressor gene. Neither has anything to do with insect toxins.
From the GATE 2019 BT paper. Every question of this paper · Download the full paper · All 4 Transgenic plants questions, with notes