Although horizontal gene transfer occurs naturally, it is infrequent and random. With the discovery of restriction enzymes and ligases it became possible to isolate parts of a genome that contained operons with a desired function and transfer them to plasmids which could then be inserted into other cells. Development of PCR combined with Sanger sequencing allowed for the more precise cloning and assembly of desired functional elements while the discovery of transposons and single strand annealing proteins enabled easier insertion of constructs into the genomic DNA of the host organism. More recently the Cas9-CRISPR system has been identified as an RNA guided restriction enzyme which can have the target sequence customized for a more precise induction of deletions at a locus (although the same effect can be attained using chemical mutagens and ionizing radiation followed by selection).

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Although this site is not for people to do your home work, however the emergence of recombinant DNA tech. has enabled the cloning of organisms including plants to improve their characteristics such as yield, disease resistant, drought resistant, by using restriction enzymes to digest the host DNA, incorporating the foreign DNA with the desired traits into a vector such as plasmids and delivering it to the host, while ligase enzyme is used to catalyze ligation or annealing of the foreign DNA to the host DNA. the CRISPR-cas9 techniques has revolutionized this technology, as it cleaves the DNA at the desired locus, thus making genome editing and customization possible.