Restriction endonuclease.
RNA Polymerase.
Step 1: Define restriction endonucleases. These enzymes, often called molecular scissors, cleave DNA at precise recognition sites. They are fundamental tools in genetic engineering for constructing recombinant DNA.
Step 2: Evaluate alternative choices.
Option (A): Incorrect. DNA ligase catalyzes the joining of DNA segments, rather than their cleavage.
Option (B): Incorrect. Ligase functions in DNA fragment ligation and is not a DNA-cutting enzyme.
Option (D): Incorrect. RNA polymerase synthesizes RNA and does not possess DNA-cutting activity. \[ \therefore \text{The correct answer is: Restriction endonuclease.} \]
Frequency of recombination between gene pairs on same chromosome as a measure of the distance between genes to map their position on chromosome, was used for the first time by