Gene therapy has gained attention during the last 25 years as it offers great promise for curing genetic diseases, but there are also risks that come with the manipulation of the genes of an entire multicellular organism. The technology for genetic modification has been around since the 1970s, but today new research on a Cas9 protein may be the key to refine the process. The first simple, chimeric recombinant DNA (recDNA) experiment was completed by Cohen and Boyer in 1972 when they successfully inserted a mammalian rRNA gene into the pSC101 E coli plasmid. They used the endonuclease, or restriction enzyme, EcoRI to remove a specific gene from the DNA of an African clawed toad by severing the DNA at specific nucleotide sequences, called cleavage recognition sites. The DNA fragment was then added to a solution of E coli plasmids, which were also treated with EcoRI, and DNA ligase was added to form bonds between the mammalian fragments and bacterial plasmids, producing transgenic recDNA. The resulting plasmids became the first, easily …show more content…
Capecchi expanded the uses of their discovery with his invention of the homologous recombination knockout mouse. Employing a procedure founded on Cohen and Boyer’s technology, he took embryonic cells from a mouse blastocyst, and replaced a specifically targeted gene with a similar, but nonfunctional, gene. Then the embryonic cells were placed into another blastocyst, which was implanted in a surrogate mother mouse with the surviving embryos allowed to grow to maturity. Pure line breeding experiments were completed with the faulty homozygous recessive genotype revealing itself as a knocked out or loss of function phenotype. Capecchi could then deduce the function of the defective gene by finding what was wrong with or missing from the mouse traits; for instance, if one of these mice never grew a hind leg, then the “knocked out” gene had to be directly involved in the development of that hind