Such crops are transgenic crops which possess and express one or more useful foreign genes or transgenes. Two unique advantages are: (a) Any gene from any organism or a gene synthesised chemically can be used for transfer and (b) Change in genotype is precisely controlled.
This technology is advantageous to breeding programmes because in the breeding activities only the already present genes are reshuffled and that changes would occur in all traits for which the parents are different.
The transgene can perform following functions.
1. Production of desired proteins:
Hirudin protein is present in leech which prevents blood clotting. Its gene was chemically synthesised and introduced in Brassica napus. The seeds of the Brassica come to have hirudin which could be extracted, purified and used as medicine.
2. Production of a desired phenotype:
Soil bacterium Bacillus thuringiensis produces a crystal (cry) protein which is toxic to larvae of certain species. There cry proteins are of various types. Each of which is toxic to a different group of insects. Cry gene (gene encoding cry protein) have been isolated and transferred into several crops (e.g., cotton). This Bt cotton is not attacked by boll worm and other insects.
3. Modify an existing biosynthetic pathway:
Transgenic Golden rice and transgenic potato produce, respectively higher content of vitamin A and protein.
4. Mask expression of a native gene:
e.g., Tomato variety “Flavr Savr” in which production of polygalacturonase was blocked. This enzyme degrades the pectin and promotes the fruit softening. In the absence of enzyme, pectin degradation is stopped and fruit remains fresh for long with a superior taste and increased total soluble solids.
Caution is required in the development of GM crops without proper safe guards because (i) Gene transfer from GM crops to weeds would make them more virulent (ii) Transgenic crops may become persistent weeds (iii) Pollen of transgenic crops may carrying the transgenes to wild relatives (iv) Transgenic crops would disturb the balance of nature and damage the ecosystem.