Process of genetic modification on plants

There are two main ways:

1) Agrobacteria tumefaciens (a natural soil bacterium that infects plants) is injected into the plant’s cells. The bacteria lodge some of its genes into the plant's genetic material, where the supposed outcome produces damaging tumors. Geneticists extract these tumour-causing genes from the bacteria and replace them with pest resistance or herbicide tolerance genes. The modified bacteria thus transfer the useful genes instead of the disease genes to the plant.

2) A gene gun is used to fire tiny gold particles coated with genes of useful traits directly into a plant's cells.


Types of GM crops

There are two main types:

1) Has the ability to tolerate herbicides that wipe out all other plants. All other plants in the field including weeds will be destroyed. This result in higher yields and reduced herbicide usage compared to conventional crops thus preserves the environment.

2) Has the ability to produce a toxin that kills pests feeding on it.

References:
http://www.guardian.co.uk/theissues/article/0,,969438,00.html
http://www.washingtonpost.com/wp-dyn/content/article/2006/12/06/AR2006120601349.html