The construction of the first recombinant DNA emerged from linking a gene encoding antibiotic resistance with a native plasmid of ____________.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Salmonella typhimurium
Option (1) Streptococcus pneumoniae — Incorrect. This bacterium causes pneumonia. Griffith used it in 1928 in his transformation experiment, long before recombinant DNA.
Option (2) Escherichia coli — Incorrect. E. coli is today the most common host in recombinant DNA work, and the vector pBR322 is an E. coli plasmid. But the first recombinant DNA used the plasmid of another bacterium.
Option (3) Staphylococcus — Incorrect. Staphylococcus is the bacterium on which Alexander Fleming was working when he discovered penicillin. It has no part in the first recombinant DNA.
Option (4) Salmonella typhimurium — Correct. Stanley Cohen and Herbert Boyer cut out the antibiotic resistance gene with a restriction enzyme and joined it to the plasmid of Salmonella typhimurium with DNA ligase. This plasmid carrying a foreign gene was the first recombinant DNA, made in 1972.
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. Stanley Cohen and Herbert Boyer accomplished this in 1972 by isolating the antibiotic resistance gene by cutting out a piece of DNA from a plasmid which was responsible for conferring antibiotic resistance.”