until a year later in 1973 that Stanley Cohen and Herbert Boyer created the first genetically
modified organism using these approaches. Combining Cohen’s expertise in plasmids and
Boyer’s expertise in restriction enzymes, a strand of DNA was cut and pasted into a plasmid
and maintained and replicated in the bacteriumE. coli. The transfer of such recombinant
Figure 7.1.The double helical structure of DNA provides the genetic instructions for the develop-
ment of an organism. The specific sequence arrangement of the bases G, A, T, and C encode regu-
latory features such as the promoter and terminator sequences of genes, and the triplet code
determines the amino acid sequence of proteins. In plants, as with all eukaryotes, most of the
DNA is packed into chromosomes and located in the cell nucleus, while in bacteria the DNA is
found directly in the cytoplasm and is most often circular.
7.1. DNA MODIFICATION 161