Re: To prove semi-conservative DNA replication

I don't know about the other experimental setting used for the proof of
semiconservative replication of DNA. Yet, smiconservative replication of
the eukaryotic chromosome was shown in the other way, namely by the
autoradiographic procedure. I found an interesting and informative web site
at which there is an explanation of the procedure
(http://www.usask.ca/biology/rank/demo/replication/replication.htm):
"An
autoradiographic procedure was first used by Taylor, Woods and Hughes
(1958) to show semiconservative replication of DNA in bean chromosomes.
3H-thymidine, was incorporated into newly replicated DNA and the location
of the radioactive label was followed in mitotic chromosomes. In a similar
way, 5 bromodeoxyuridine, BUdR, can be used as a precursor for DNA
synthesis and its location in the replicated mitotic chromosomes monitored
as bright orange / yellow chromosomes. In the BUdR procedure, DNA is
replicated for two generations in BUdR and chromosomes are viewed at the
first and second mitotic metaphase by fluorescence microscopy as harlequin
chromosomes. When both strands of DNA are labeled, BUdR-labeled chromosomes
and chromatids fluoresce a lighter color than when only one antiparallel
strand has incorporated BUdR."

Also, very nice interpratation could be found at http://www.http://www.tusculum.edu/faculty/home/ivanlare/html/genetics/dnareplication-master.html

"# Taylor, Woods, and Hughes' experiment with eukaryotes

   1. Background

         1. There are several isotopes of hydrogen, one of which, 3H, is
radioactive

         2. 3
            H containing nucleotides will be incorporated into DNA

         3. The radioactive DNA can be detected using photographic film

               1. The process, called autoradiography, turns the film dark
where it was exposed to particles released during radioactive decay

   2. Experiment

         1. Broad beans were grown in media containing 3H-thymidine for
approximately the time it took the actively dividing root cells to undergo
one generation

         2. They were then changed to media with only cold
(non-radioactive) nutrients

   3. Predictions

         1. Conservative model of replication

               1. This model would predict that only one chromatid on each
chromosome would be radioactive (expose the film) while the other
chromatids would be cold

         2. Semiconservative model of replication

               1. This model would predict that radioactivity would be
equally distributed throughout the whole chromosome

   4. Results and interpretation

         1. The results were compatible with the semiconservative method of
DNA replication"