Genetic Engineering : DNA Duplication
This discovery was a turning point in the development of genetic engineering. Scientists use bacteria for
these experiments because they are simple organismsthat multiply quickly. Researchers can see the results
of their work almost immediately, and they can produce large quantities of new substances in a short per
iod of time. Scientists already knew that bacteria havesmall, circular pieces of DNA called plasmids floating
freely within their cytoplasm. When restriction enzyrnes were discovered, scientists wondered if they
coul(l be used to cut and recombine different organisms at the molecular level. They hoped they could
pick specific desirable traits from one organism and transfer them to another organism without getting unw
anted characteristics as well.
This discovery was a turning point in the development of genetic engineering. Scientists use bacteria for
these experiments because they are simple organismsthat multiply quickly. Researchers can see the results
of their work almost immediately, and they can produce large quantities of new substances in a short per
iod of time. Scientists already knew that bacteria havesmall, circular pieces of DNA called plasmids floating
freely within their cytoplasm. When restriction enzyrnes were discovered, scientists wondered if they
coul(l be used to cut and recombine different organisms at the molecular level. They hoped they could
pick specific desirable traits from one organism and transfer them to another organism without getting unw
anted characteristics as well.
Researchers found that after a gene had been isolated, they could apply an enzyme called ligose.—
“molecular glue”—to splice the gene to another DNA fragment. This process would seal the plasmid with
the new gene inside. After that, every time the bacteria reproduced, they would also reproduce the new gene
contained in the plasmid.In 1973, Stanley Cohen of Stanford University and Herbert Boyer of the University of California in San Francisco successfully completed this procedure.They took a gene from a toad, and, using restriction enzymes, cut and pasted it into Es chericliia coil (E.coli) bacteria—microscopic organisms that can be found in the human intestines. more of a challenge. Eventually, scientists learned to clone cows and sheep by splitting embryos. It became common for (:attle ranchers to clone animals with desirable characteristics. In July 1996, Dr. Ian Wilmut of the Roslin Institute in Scotland took cloning one step further. He succeeded in cloning a sheep named Dolly with DNA taken from an adult sheep’s cell. Seine researchers feel that cloning will make genetic engineering more efficient. For instance, if researchers spent a long time developing a genetically engineered
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