All
Cases
of
Genes
are
DNA
The genes of almost all organisms are DNA. This is shown by the following observations.
(I) Genetic transformation experiments of Avery, Macleod and McCarty (1944) first clearly established the role of DNA as genetic material, and gave evidence of the chemical nature of the gene. DNA was isolated from a virulent strain of bacteria. An avirulent strain was grown in a medium containing this DNA.
After some time virulent bacteria could be isolated from the medium. These could reproduce indefinitely, producing virulent strains. It is apparent that genes (DNA) from the virulent strain when introduced into the avirulent strain transformed the latter into the virulent strain. When DNase, an enzyme which breaks down DNA, was added to the medium no transformation occurred.
This
confirmed
the
fact
that
transformation
was
due
to
DNA
and
not
because
of
any
impurities
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