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 answer 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. **Understanding Recombinant DNA (rDNA)**:
- Recombinant DNA is formed by combining DNA from two different sources. In this case, it involves linking an antibiotic resistance gene with a plasmid.

2. **Identifying the Components**:
- The antibiotic resistance gene is isolated from a source (in this case, a plasmid).
- The native plasmid of Salmonella typhimurium serves as the vector for the recombinant DNA.

3. **Historical Context**:
- The first successful construction of rDNA occurred in the early 1970s. This was a significant milestone in biotechnology.

4. **Key Scientists Involved**:
- The scientists credited with this groundbreaking work are Stanley Cohen and Herbert Boyer. They successfully linked the antibiotic resistance gene to the plasmid.

5. **The Process**:
- In 1972, Cohen and Boyer isolated the antibiotic resistance gene from a plasmid and inserted it into the plasmid DNA of Salmonella typhimurium. This new plasmid could now replicate and express the antibiotic resistance gene.

6. **Conclusion**:
- The correct answer to the question is that the first recombinant DNA was constructed by Stanley Cohen and Herbert Boyer in 1972.

### 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.