Which of the following plasmids from Agrobacterium tumefaciens has been modified into a cloning vector?

Ti-plasmid

The correct answer is Option (3) -Ti-plasmid

The process of transferring genes into plants and animals has been inspired by the mechanisms used by bacteria and viruses to deliver genes into eukaryotic cells. For instance, Agrobacterium tumefaciens, a pathogen of certain dicot plants, can transfer a segment of DNA known as 'T-DNA' to transform normal plant cells into tumor cells and direct them to produce specific chemicals for the pathogen's benefit. Similarly, retroviruses in animals can transform normal cells into cancerous cells.

By studying how pathogens deliver genes into their eukaryotic hosts, scientists have gained valuable insights into using these mechanisms to deliver genes of interest to humans.

The tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens has been modified into a cloning vector, making it non-pathogenic to plants while retaining its ability to deliver genes of interest into various plants. Similarly, retroviruses have been disarmed and are now employed as vectors to deliver desired genes into animal cells.

Once a gene or DNA fragment is inserted into a suitable vector, it is transferred into a bacterial, plant, or animal host, where it can replicate and produce the desired effects. This process has opened up exciting possibilities for genetic engineering and gene transfer to achieve various beneficial outcomes.