A foreign DNA and plasmid cut by the same restriction endonuclease can be joined to form a recombinant DNA by :

Options

A. EcoRl
B. Taq polymerase
C. DNA polymerase III
D. DNA ligase

Answer

To solve the question regarding how a foreign DNA and plasmid cut by the same restriction endonuclease can be joined to form recombinant DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases are enzymes that cut DNA at specific sequences. When both the foreign DNA and plasmid DNA are cut by the same restriction enzyme, they will have complementary sticky ends.

**Hint**: Remember that restriction endonucleases create specific cuts in DNA, allowing for compatible ends.

2. **Formation of Sticky Ends**:
- The cuts made by the restriction endonuclease result in sticky ends on both the foreign DNA and the plasmid. These sticky ends are crucial because they allow the two DNA fragments to align and bind together.

**Hint**: Sticky ends are essential for the joining process; they facilitate the binding of two DNA fragments.

3. **Joining the DNA Fragments**:
- To join the two DNA fragments (the foreign DNA and the plasmid), an enzyme called DNA ligase is used. DNA ligase facilitates the formation of phosphodiester bonds between the adjacent nucleotides, effectively sealing the nicks in the sugar-phosphate backbone of the DNA.

**Hint**: DNA ligase is the enzyme responsible for joining DNA fragments together.

4. **Final Result**:
- The result of this process is the formation of recombinant DNA, which contains genetic material from both the foreign DNA and the plasmid.

**Hint**: The final product is recombinant DNA, which can be used for various applications in genetic engineering.

### Conclusion:
The correct answer to the question is that a foreign DNA and plasmid cut by the same restriction endonuclease can be joined to form recombinant DNA by **DNA ligase**.