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Before the After one switch round of to 14N replication

After two After three rounds of rounds of replication replication

Before the After one switch round of to 14N replication

After two After three rounds of rounds of replication replication two bands should be present. Subsequent rounds of replication will increase the fraction of DNA consisting entirely of new 14N, thus the upper band will get darker. However, the original DNA with 15N will remain, so two bands will be present.

2. Consider the experiment conducted by Meselson and Stahl in which they used 14N and 15N in cultures of E. coli and equilibrium density gradient centrifugation. Draw pictures to represent the bands produced by bacterial DNA in the density-gradient tube before the switch to medium containing 14N and after one, two, and three rounds of replication after the switch to the medium containing 14N. Use a separate set of drawings to show the bands

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