In 1958 Matt Meselson, whom I knew slightly at Harvard (he was a terrific guy), performed, along with Frank Stahl, an experiment that John Cairns called “the most beautiful experiment in biology”. What he and Stahl did (see description here) was to use density-labeled components of DNA to choose among which of the three methods of DNA replication floated at the time was correct (people didn’t know how DNA replicated in 1958; this experiment settled the issue):
In “semi-conservative replication”, each strand of DNA unwinds and makes a copy of itself, so that each DNA helix in the next generation of DNA has both a parental strand and a new strand synthesized from nucleotides and sugars. “Conservative” replication involves each double strand making another whole double strand. “Dispersive” replication involved the DNA breaking, with each break synthesizing new DNA, matched to the other strand, in bits. They’re portrayed…
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The Logical Place 