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Semiconservative replication of DNA was first demonstrated in
A
$Salmonella\ typhimurium$
B
$Drosophila\ melanogaster$
C
$Escherichia\ coli$
D
$Streptococcus\ pneumoniae$
Detailed Solution
Matthew Meselson and Franklin Stahl (1958) proved that DNA replicates semiconservatively.
They grew $E.\ coli$ for many generations in a medium containing $^{15}NH_4Cl$ as the only nitrogen source, so that its DNA became heavy.
The cells were then transferred to a normal $^{14}NH_4Cl$ medium and DNA was extracted at definite intervals and centrifuged in a CsCl density gradient.
After one generation (20 minutes) the DNA had an intermediate (hybrid) density; after two generations (40 minutes) equal amounts of hybrid and light DNA were found.
This showed that each new DNA molecule has one parental and one newly synthesised strand.
Hence it was first demonstrated in $Escherichia\ coli$.
They grew $E.\ coli$ for many generations in a medium containing $^{15}NH_4Cl$ as the only nitrogen source, so that its DNA became heavy.
The cells were then transferred to a normal $^{14}NH_4Cl$ medium and DNA was extracted at definite intervals and centrifuged in a CsCl density gradient.
After one generation (20 minutes) the DNA had an intermediate (hybrid) density; after two generations (40 minutes) equal amounts of hybrid and light DNA were found.
This showed that each new DNA molecule has one parental and one newly synthesised strand.
Hence it was first demonstrated in $Escherichia\ coli$.