In gene-cloning projects, plasmids function to allow replication of the DNA that's being cloned. Gene cloning describes the process of copying fragments of DNA which can then be used for many different purposes, such as creating genetic modified crops. There may be two types; in vitro which involves using polymerase chain reaction to create copies of DNA fragments or the in vivo which involves use of restriction enzymes and ligases using vectors and cloning the fragments into host cells.