Genetically Modified Crops and Pest Resistance: Quick Revision

A brief note on Genetically Modified Crops and Pest Resistance. Read it before a test. Try each question at the end before you open its answer.

GM crops

• Three options for more food: agro-chemical based, organic and genetically engineered crop based agriculture.
• GMO: a plant, bacterium, fungus or animal whose genes have been altered by manipulation. A transgenic organism carries a gene from another species.
• Gains: tolerance to cold, drought, salt and heat; less need for chemical pesticides; fewer losses after harvest; better use of minerals; better nutrition (vitamin A enriched rice).
• Tailor-made plants: starches, fuels and pharmaceuticals for industry.

The Bt toxin

• Source: the soil bacterium Bacillus thuringiensis. It forms protein crystals that hold an inactive protoxin.
• Action: the alkaline gut of the insect dissolves the crystals. The toxin becomes active, binds to the midgut epithelial cells, and makes pores. The cells swell and burst.
• Genes: cryIAc and cryIIAb for the cotton bollworms, cryIAb for the corn borer.
• Target groups: lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), dipterans (flies, mosquitoes).
• Crops: cotton, corn, rice, tomato, potato and soyabean.

RNA interference

• A double stranded RNA that is complementary to an mRNA silences it, so the mRNA is not translated.
• The tobacco plant was given nematode specific genes with an Agrobacterium vector. It made sense and antisense RNA, which formed dsRNA, and the nematode Meloidogyne incognita could not survive.
• This part is not in the NEET syllabus text, but A-Level and IB ask it.

A worked example

A plot has 250 larvae. On Bt cotton, 90 per cent of them die. How many survive?

1. The survivors are $100 - 90 = 10$ per cent.
2. The number is $0.10 \times 250 = 25$ larvae.

Practice with new numbers

A program to try

The program looks up the pest that each gene controls.

Mistakes to avoid

• Saying that the crystal holds an active toxin. It holds the inactive protoxin.
• Placing the activation in an acidic gut. It is the alkaline gut.
• Mixing up the genes. cryIAb is for the corn borer.
• Calling a GM plant a hybrid. A hybrid comes from a cross.

Check yourself

1. Which pH of the gut makes the Bt toxin active?

2. Name two genes that control the cotton bollworms.

3. What is a transgenic organism?

4. What does a double stranded RNA do to a matching mRNA?

Sources

• OpenStax Biology 2e, chapter 17, Biotechnology and Genomics.
• NCERT (2023). Biology, Textbook for Class XII, chapter 10, Biotechnology and Its Applications.