Human DNA cut with restriction enzyme A can be joined to:

• A. A bacterial plasmid cut with restriction enzyme A.
• B. Human DNA cut with restriction enzyme B.
• C. Human DNA that is uncut.
• D. A bacterial plasmid that is uncut.

Answer: (A)

Verified step by step guidance

1. Understand the role of restriction enzymes: Restriction enzymes are proteins used to cut DNA at specific sequences. Each enzyme recognizes a specific sequence and cuts the DNA at or near this site.
2. Recognize the concept of 'sticky ends': When DNA is cut by a restriction enzyme, it often leaves overhanging sequences known as 'sticky ends'. These ends can pair with complementary sequences, facilitating the joining of DNA fragments.
3. Identify the compatibility of sticky ends: For two DNA fragments to be joined, they must have compatible sticky ends. This means they should be cut by the same restriction enzyme or by enzymes that produce compatible ends.
4. Apply this to the problem: Human DNA cut with restriction enzyme A will have specific sticky ends. To join this DNA with another piece, such as a bacterial plasmid, the plasmid must also have compatible sticky ends, which would be the case if it is cut with the same restriction enzyme A.
5. Conclude the compatibility: Therefore, a bacterial plasmid cut with restriction enzyme A can be joined to human DNA cut with the same enzyme, as they will have complementary sticky ends that can anneal and be ligated together.