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 that cut DNA at specific sequences. Each enzyme recognizes a particular 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 ends known as 'sticky ends'. These sticky ends can pair with complementary sequences, allowing DNA fragments to be joined together.
3. Identify the compatibility of sticky ends: DNA fragments cut with the same restriction enzyme will have compatible sticky ends, meaning they can be joined together. This is crucial for the process of DNA ligation.
4. Apply this knowledge to the problem: Human DNA cut with restriction enzyme A will have sticky ends that are compatible with any other DNA cut with the same enzyme, such as a bacterial plasmid cut with restriction enzyme A.
5. Consider the options: Human DNA cut with restriction enzyme A can be joined to a bacterial plasmid cut with restriction enzyme A because they have compatible sticky ends. Other options, such as DNA cut with different enzymes or uncut DNA, will not have compatible ends for joining.