Retroviruses in animals, including humans, have the ability to transform normal cells into:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Cancerous cells
Some pathogens have long known how to put their genes into the cells of their hosts. Agrobacterium tumefaciens turns normal plant cells into a tumour. In the same way, retroviruses in animals can transform normal cells into cancerous cells. Scientists have disarmed retroviruses and now use them to deliver desirable genes into animal cells.
Option (1) Competent cells — Incorrect. Competent cells are bacterial cells treated with a divalent cation such as calcium so that they can take up DNA. Retroviruses do not do this.
Option (2) Cancerous cells — Correct. Retroviruses change normal animal cells into cancerous cells. This ability to deliver genes is what makes disarmed retroviruses useful as vectors.
Option (3) Recombinant bacterial cells — Incorrect. Recombinant bacterial cells are made in the laboratory when a bacterium takes up recombinant DNA. Retroviruses infect animal cells, not bacteria.
Option (4) Antibiotic-resistant cells — Incorrect. Antibiotic resistance comes from resistance genes such as ampR, used as selectable markers in E. coli. It is not what retroviruses produce in animal cells.
NCERT Extract:
Cloning Vectors – “… For example, Agrobacterium tumifaciens, a pathogen of several dicot plants is able to deliver a piece of DNA known as ‘T-DNA’ to transform normal plant cells into a tumor and direct these tumor cells to produce the chemicals required by the pathogen. Similarly, retroviruses in animals have the ability to transform normal cells into cancerous cells. … Similarly, retroviruses have also been disarmed and are now used to deliver desirable genes into animal cells.”