Why we make genetically modified crops

A farmer's problem

A farmer wants a bigger harvest from the same field. For many years the answer was a better seed, more fertiliser and more spray against pests. This worked well. The green revolution tripled the food supply of the world. But the number of people kept rising, and the extra food was not enough.

There was another trouble. Most of the gain came from better farm management and from agrochemicals, which are fertilisers and pesticides. For farmers in the developing world these are often too costly. And with the methods of conventional breeding, a further rise in the yield of the existing varieties was not possible.

So scientists asked a new question. Could the plant itself be changed, so that it needs less help from chemicals?

Three options for more food

NCERT names three ways to increase food production.

This chapter is about the third option. In the previous chapter you met the tools: restriction enzymes, ligases, vectors, PCR and the ways to put a gene into a host. Here we use them on farms and in hospitals. We do not repeat the tools.

What is a GMO?

Plants, bacteria, fungi and animals whose genes have been altered by manipulation are called genetically modified organisms, or GMOs. A plant that is a GMO is a GM plant.

When the new gene comes from another species, the organism is transgenic, and the foreign gene is a transgene. Not every GMO has a foreign gene: sometimes a gene of the plant itself is changed or switched off. Most examples in this chapter are transgenic.

Do not confuse a GM plant with a hybrid. A hybrid comes from a cross between two parents of the same or a close species, and it mixes thousands of genes. A GM plant gets one gene, or a few, put in by a vector, and the gene may come from a bacterium or an animal.

What genetic modification has done for crops

GM plants have been useful in several ways. NCERT lists five.

1. Tolerance to abiotic stresses. Abiotic means non-living. Crops have been made more tolerant to cold, drought, salt and heat.
2. Less reliance on chemical pesticides. Pest resistant crops are attacked less, so fewer sprays are needed.
3. Fewer losses after harvest. Grain and fruit last longer, so less is wasted before it reaches the buyer.
4. Better use of minerals. Plants take up minerals more efficiently. This stops the fertility of the soil from being used up early.
5. Better nutrition. For example, rice that is enriched with vitamin A.

Genetic modification has also been used to make tailor-made plants. These supply raw material to industry, in the form of starches, fuels and pharmaceuticals.

A look at vitamin A rice

Ordinary rice grain has almost no provitamin A. This is a substance, called beta-carotene, that the body changes to vitamin A. People who eat mostly rice may lack vitamin A, and a lack of it harms the eyes. Genes of the pathway that makes beta-carotene were put into rice, and the grain became yellow. NCERT calls it vitamin A enriched rice, and the common name is golden rice.

Notice that the saving can be negative. If the seed costs a lot and few sprays are saved, the farmer loses money. A real decision uses real prices.

Try it in Python

The program places six examples under the gain that each one shows.

Practise with new numbers

Common mistakes

• Saying that only plants can be genetically modified. Bacteria, fungi and animals are GMOs too.
• Calling a GM crop a hybrid. A hybrid is made by a cross. A GM crop gets a gene by gene transfer.
• Saying that every GMO is transgenic. A gene can be changed in place, without a foreign gene.
• Thinking that vitamin A rice has vitamin A itself. It has the provitamin, beta-carotene, which the body changes.

Remember these

• Three options: agro-chemical based, organic and genetically engineered crop based agriculture.
• GMOs are plants, bacteria, fungi or animals with altered genes.
• Gains: stress tolerance, less pesticide, fewer losses after harvest, better use of minerals, better nutrition.
• GM plants can also give starches, fuels and pharmaceuticals.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Name the three options that NCERT gives for a rise in food production.

2. What is a GMO? Give two kinds of organism that can be one.

3. Give three ways in which genetic modification has helped crops.

4. How is a GM plant different from a hybrid?

5. What does vitamin A enriched rice contain, and why is it useful?

References

• OpenStax Biology 2e, chapter 17, Biotechnology and Genomics, section 17.1 Biotechnology.
• NCERT (2023). Biology, Textbook for Class XII, chapter 10, Biotechnology and Its Applications.