Construction of first rDNA by linking a gene encoding antibiotic resistance gene with native plasmid of Salmonella typhimurium was done by:

Options

A. Smith and Wilson
B. A. Tiselius
C. Stanley Cohen and Herbert Boyer
D. Arber and Nathan

Answer

To solve the question regarding the construction of the first recombinant DNA (rDNA) by linking a gene encoding antibiotic resistance with the native plasmid of Salmonella typhimurium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Scientists Involved**: The first rDNA was constructed by Stanley Cohen and Herbert Boyer. They are credited with pioneering techniques in genetic engineering.

2. **Understand the Source of the Gene**: The gene encoding antibiotic resistance was derived from a plasmid found in the bacterium Salmonella typhimurium. Plasmids are small, circular DNA molecules that can replicate independently of chromosomal DNA.

3. **Cutting the DNA**: Cohen and Boyer used restriction enzymes to cut the DNA from the plasmid that carries the antibiotic resistance gene. Restriction enzymes act as molecular scissors that can cut DNA at specific sequences.

4. **Linking the DNA**: After cutting the DNA, they linked the antibiotic resistance gene to a plasmid vector from E. coli. This process involved using DNA ligase, an enzyme that facilitates the joining of DNA strands.

5. **Transformation**: The recombinant plasmid (containing the antibiotic resistance gene) was then introduced into E. coli cells through a process called transformation. This allowed the E. coli to express the antibiotic resistance gene.

6. **Conclusion**: The successful linking of the antibiotic resistance gene with the plasmid of Salmonella typhimurium resulted in the first recombinant DNA. Thus, the correct answer to the question is Stanley Cohen and Herbert Boyer.

### Final Answer:
The construction of the first rDNA by linking a gene encoding antibiotic resistance with the native plasmid of Salmonella typhimurium was done by **Stanley Cohen and Herbert Boyer**.

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