ABSTRACT
Restriction enzymes recognize specific recognition sequences and cut the DNA to leave cohesive ends or blunt ends. The ends of restricted DNA molecules can be joined together by ligation to create new recombinant DNA molecules. Restriction enzymes are isolated from bacteria, where they play a role in protecting the host cell against virus infection. When a DNA molecule is cut by a restriction enzyme, the DNA fragments from that restriction digest can be separated by gel electrophoresis. By separating the restriction fragments and measuring their sizes by gel electrophoresis, it is possible to deduce where on the DNA molecule each restriction enzyme cuts. Analysis of human genomic DNA has revealed that there are many differences in DNA sequence between individuals that have no obvious effect, often because the changes lie in introns or between genes.
