Assertion: Restriction endonucleases are also called "molecular scissors"
Reason: When fragments generated by restriction endonucleases are mixed, they join together due to their sticky ends.

Both Assertion (A) and Reason (R) are correct but R is not the correct explanation of A.

The correct anser is Option (2)- Assertion and reason are correct but reason is not the correct explanation of assertion.

The assertion that restriction endonuclease are also called molecular scissors is correct.Restriction endonuclease are enzymes that cut DNA molecules at specific recognition sequence s.Thesr enzymes play a crucial role in genetic engineering and molecular biology by allowing scientists to precisely manipulate DNA sequences.

In reason, it's true that fragments generated by restriction endonuclease can have "sticky ends"( single - stranded overhang), these ends donot spontaneously join together when mixed.Instead, they can anneal with complementary sticky ends from other DNA fragments, facilitated by base pairing between the complementary nucleotides.This process is known as DNA ligation, and it typically requires an additional enzyme called DNA ligase to catalyze the joining of DNA fragments.so DNA ligase is important here to complete the process.