= Meselson-Stahl experiment
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The <Meselson-Stahl experiment> tested how parental strands are distributed during <DNA replication>. <Escherichia coli> grown with heavy <nitrogen> were transferred to light-nitrogen medium. Extracted <DNA> was separated by buoyant density in a caesium-chloride gradient using <analytical ultracentrifugation>; ultraviolet imaging located the bands. <The replication of DNA in Escherichia coli by Matthew Meselson and Franklin W. Stahl>[1958, Figures 1–4 and Experimental: density-gradient separation and ultraviolet photographs]{ref}
After one generation, the main <DNA> band had intermediate density, contrary to the separate heavy and light populations predicted by a conservative-copying model. After two generations, intermediate and light bands supported <semiconservative replication> over a uniformly dispersive model. Under ideal synchronous doubling, the fraction of duplexes retaining an original heavy strand after $n\geq1$ generations is $2^{1-n}$. The experiment inferred strand inheritance from density distributions; it did not directly photograph separately coloured strands.
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