Transgenic plants and animals. Hybridoma

In ordinary breeding unwanted genes pass into the plant too, whereas genetic engineering lets one insert a single needed gene. A natural vector is the Ti plasmid of the soil bacterium Agrobacterium tumefaciens: it enters a dicot plant, joins its T-DNA segment to the plant chromosome and causes a tumour. Scientists remove the tumour-causing genes from the T-DNA and put the needed gene in their place – a vector construct (transferred to a smaller plasmid such as pBR322). A harmless agrobacterium carrying this vector transforms plant cells. Other methods are gene guns (shooting tiny particles coated with the gene into cells) and strong electric fields. Transformed cells grow on nutrient medium into a callus (a mass of uniform cells); under plant hormones a whole plant develops from the callus; each of its cells has the foreign gene, and it is passed on in sexual reproduction. Examples: insect-resistant Bt cotton and maize (a protein gene from Bacillus thuringiensis), herbicide-tolerant soya, “golden rice” rich in vitamin A. Transgenic plants can raise yields and reduce pesticides; at the same time their safety is tested, their effect on the environment is studied, and in many countries products are labelled and controlled by law.