Gene engineering in bacterial plasmids
Plasmids are extracted from bacteria. Though we only show a few copies, millions are used. The plasmids have a gene that causes ampicillin resistence in the bacteria. They are mixed
with an enzyme that is known to cut genetic material at a specific marker. In the plasmids, it will cut the
gene that turns the bacteria blue in the presence of lactose. This renders the "blue" gene ineffective. The same enzyme is mixed with dna that contains a gene that we want to
duplicate. The enzyme also cuts DNA at marker points that create both the gene we want as well as many other small pieces. All the resulting pieces are mixed with our
plasmids. Some plasmids reconnect naturally and have "blue" genes that function. Others combine with the gene we want in the middle of the "blue" gene so that gene remains ineffective.
The resulting plasmids are introduced to bacteria which take up some of the plasmids. All of the new plasmids contained a gene for ampicillin resistence, so the bacteria that have taken up
the new plasmids are ampicillin resistant. If we place them in a culture medium with lactase and ampicillin, the bacteria with out new plasmids die off. The ones with new plasmids grow because
they now are resistant. If the plasmid had our desired piece of genetic material, the plasmid gene for turning blue in the presence of lactose is broken- so if the new gene is present, bacteria
colonies are white. If the "blue" gene is intact and our desired gene isn't present, the colonies are blue.
