The first instance of construction of an artificial recombinant DNA molecule was carried out on the plasmid of:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Salmonella typhimurium
Option (1) Bacillus thuringiensis — Incorrect. This bacterium is the source of the Bt toxin genes used in Bt crops, much later.
Option (2) Escherichia coli — Incorrect. E. coli is the usual host for cloning; the first recombinant DNA was made from a plasmid of another bacterium.
Option (3) Agrobacterium tumefaciens — Incorrect. Its Ti plasmid was later developed as a vector for plants.
Option (4) Salmonella typhimurium — Correct. Cohen and Boyer did it in 1972 by linking an antibiotic resistance gene to its plasmid.
NCERT Extract:
Principles of Biotechnology – “… Let us now focus on the first instance of the construction of an artificial recombinant DNA molecule. The construction of the first recombinant DNA emerged from the possibility of linking a gene encoding antibiotic resistance with a native plasmid (autonomously replicating circular extra-chromosomal DNA) of Salmonella typhimurium.”