Page 36 - The Evolution Impasse 1

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are countless genetic variations. Some of Genes are transmitted between bac-
them, as mentioned above, have genetic teria by means of plasmids, tiny DNA
information that gives them resistance to circles in bacteria in which resistance
some medicines. When bacteria are ex- genes are often found encoded. These
posed to a certain medicine, the non-re- genes allow the bacteria to become resis-
sistant variations are killed off. But the tant to various toxic materials in their
resistant variations survive and multiply surroundings.
even more. After a while, the rapidly Resistance genes may also be found
multiplying resistant bacteria take the in the chromosomal DNA in bacteria. A
place of the non-resistant bacteria that chromosome is much larger than the
had been destroyed. Then, since most plasmids in bacterial cells; it is a mole-
bacteria in a colony are resistant to that cule that determines the cells’ function
particular antibiotic, it becomes ineffec- and division.
tive against them. A bacterium with genetic immunity
But the bacteria are the exact same to antibiotics can transfer its genetic in-
species of bacteria. There was no pro- formation through plasmids to another
cess of evolution. bacterium. Resistance genes are someti-
mes transferred through viruses. In this
Transmission of resistance case, a virus transfers the resistance gene
among different species of it withdrew from one bacterium to anot-
bacteria her. And when a bacterium dies and di-

Not only can some bacteria inherit sintegrates, another bacterium can ab-
their resistance to antibiotics from pre- sorb the resistance gene it releases into
vious immune generations; they can also the immediate environment.
have resistance genes from other bacteri- A non-resistant bacterium can easily
a transferred to them. add this gene to its own DNA molecules,

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T There were resistant bacteria before the discovery of antibiotics. .
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B Bacteria did not develop resistance after being exposed to antibiotics. .
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THE EVOLUTION IMPASSE I