Assertion (A): Scientists can cut apart and paste together DNA molecules at will, regardless of the source of the molecules. Reason (R): DNA fragments can be manipulated using restriction endonucleases and DNA ligases.

1. Assertion (A): Scientists can cut apart and paste together DNA molecules at will, regardless of the source of the molecules. This describes the fundamental principle of recombinant DNA technology. Using specific enzymes, DNA segments from different organisms can be cut and joined. So, the assertion is true. 2. Reason (R): DNA fragments can be manipulated using restriction endonucleases and DNA ligases. This statement is also true. Restriction endonucleases ('molecular scissors') recognize specific DNA sequences and cut the DNA at these sites. DNA ligases ('molecular glue') join DNA fragments together by forming phosphodiester bonds. 3. The ability to use these enzymes (restriction endonucleases to cut and DNA ligases to paste) is precisely what allows scientists to cut apart and paste together DNA molecules from different sources. 4. Therefore, both Assertion (A) and Reason (R) are individually true, and Reason (R) is the correct explanation of Assertion (A).