E.coli cloning vector pBR322 contains antibiotic resistance genes for Ampicillin (ampR) and Tetracycline (tetR) as selectable markers.

Explanation:
The correct answer is option B, which states that the two antibiotic resistance genes on vector pBR322 are Ampicillin and Tetracycline.

Vector pBR322:
- Vector pBR322 is a commonly used plasmid vector in molecular biology. It was one of the first widely used cloning vectors and has been extensively studied and characterized.
- It is a circular double-stranded DNA molecule that can replicate independently of the chromosomal DNA in bacterial cells.
- pBR322 contains multiple restriction enzyme recognition sites, allowing the insertion of foreign DNA fragments for cloning purposes.
- It also carries two antibiotic resistance genes, which are essential for selection and maintenance of the vector in bacterial cells.

Antibiotic Resistance Genes on pBR322:
- Ampicillin Resistance Gene (AmpR): The pBR322 vector carries a gene that confers resistance to the antibiotic ampicillin. This gene encodes an enzyme called β-lactamase, which inactivates the ampicillin by hydrolyzing its β-lactam ring. Bacteria that contain this gene can grow and survive in the presence of ampicillin.
- Tetracycline Resistance Gene (TetR): The pBR322 vector also carries a gene that provides resistance to the antibiotic tetracycline. This gene encodes a protein called TetR, which binds to tetracycline and prevents its inhibitory effects on bacterial protein synthesis. Bacteria that contain this gene can grow and survive in the presence of tetracycline.

Importance of Antibiotic Resistance Genes:
- The presence of antibiotic resistance genes in pBR322 allows for the selection and maintenance of the vector in bacterial cells.
- When the vector is introduced into bacterial cells, those cells that do not contain the resistance genes will be killed by the antibiotics, while those that have taken up the vector will survive and propagate.
- This selective pressure ensures that only the cells containing the desired vector and any inserted foreign DNA fragments will be able to grow and form colonies.

In summary, the two antibiotic resistance genes on vector pBR322 are Ampicillin and Tetracycline. These genes provide resistance to the antibiotics ampicillin and tetracycline, respectively, and allow for the selection and maintenance of the vector in bacterial cells.