Question

A farmer grew two varieties of corn crop in field A and B. He grew normal corn crops in field A and GM corn crops in field B.

He observed that corn borers attacked only in field A. To control it, spores of Bt were sprayed on field A.

1. Name the gene in the spores responsible for control of pest.     [0.5]
2. What effect will the spores of Bt have on insect pest?     [1.5]
3. How has corn plants of field B developed resistance against this pest? Explain.     [1]

Answer 1

1. The cry (crystal) gene from Bacillus thuringiensis (encoding Cry or δ‑endotoxin proteins, e.g., cry1Ab).
2. Bt produces Cry (Bt) toxin as an inactive crystal. When insect larvae ingest it, the alkaline gut activates the toxin; the activated toxin binds midgut epithelial cells and forms pores, causing cell swelling, lysis, gut paralysis, cessation of feeding and death of the larva.
3. Field B corn is genetically modified (transgenic) to carry the Bt cry gene inserted into the plant genome. The plants express the Bt (Cry) toxin in their tissues, so larvae that feed on them ingest the toxin and are killed, conferring resistance to corn borer.