Genetic engineering has been successfully used for producing transgenic mice. Many transgenic mice are designed to increase our understanding of how genes contribute to development of diseases. Transgenic mice are being developed for use in testing the safety of vaccine before they are used in human beings. For example transgenic mice are being used to test the safety of polio vaccine.

The genetically modified brinjal in India has been developed for insect resistance. Bt brinjal is a transgenic brinjal that is developed by inserting a crystal gene from the Bacillus thuringiensis into the brinjal’s genome. This process of insertion is accomplished using Agrobacterium mediated recombination.

Transgenic plants are the ones generated by introducing foreign DNA into a cell and regenerating a plant from that cell.

About Bt toxin, it is true, that the inactive protoxin gets converted into active form in the insect gut. There are several advantages in expressing Bt toxins in transgenic Bt crops. The level of toxin expression can be very high, thus delivering sufficient dosage to the pest.The toxin expression is contained within the plant system and hence only those insects that feed on the crop perish.The toxin expression can be modulated by using tissue-specific promoters and replaces the use of synthetic pesticides in the environment.

Agrobacterium tumefaciens is the causal agent of crown gall disease (the formation of tumours) in over 140 species of dicot. This disease caused by a DNA plasmid(T_i plasmid) carried by bacterium and transferred to the plant cells. T_i plasmid has widely used in plant engineering as a vector in order to inject gene in host plant to form transgenic plant.