In a genetic engineering experiment, restriciton enzymes can be used for

Restriction enzymes, also called restriction endonucleases, bind to DNA and cleave the double strand, forming smaller pieces of DNA. There are three types of restriction enzymes; Type I restriction enzymes recognize a DNA sequence and cut the strand randomly more than one thousand base pairs away from the site. Type II restriction enzymes, the most useful for molecular biology laboratories, recognize and cut the DNA strand predictably at a specific sequence which is usually less than ten base pairs long. Type III restriction enzymes are similar to Type I, but these cut the DNA about thirty base pairs from the recognition sequence.